philosophy and the sciences - phil. sci. course

Definition: An argument is deductively valid if and only if it is impossible that its conclusion is false while its premises are true.. Remember: This definition is the same as the defin

Deductive and Inductive Logic

What is Reasoning?

Example: The first theorem Euclid’s Elements provides a good example of the kind of

reasoning that people admire

Suppose we construct a triangle in the following way: 1 Draw a circle centered at point A Mark a point B on the circumference and draw a line from A to B Draw a second circle

centered at B that passed through A Mark one of the points at which the circles intersect as B and draw lines from C to A and from C to B

Theorem: All the sides of the triangle ABC are of equal length

Proof: Let |AB| denote the length of the line segments AB, and so on

Step 1: |AB| = |AC| because they are radii of the circle centered at A

Step 2: |BA| = |BC| because they are radii of the circle centered at B

Step 3: |AB| = |BA| because AB and BA denote the same line

Step 4: |AC| = |BC| because they are each equal to the same thing (viz |AB| ).Step 5: Therefore, |AB| = |AC| = |BC| by steps 1 and 4

Definition: An argument is a list of statements, one of which is the conclusion and the rest of which are the premises

The conclusion states the point being argued for and the premises state the reasons being advanced in support the conclusion They may not be good reasons There are good and bad arguments

Tip: To identify arguments look for words that introduce conclusions, like "therefore",

"consequently", "it follows that" These are called conclusion indicators Also look for premise indicators like "because" and "since"

Remark: Each of the five steps in the proof to Euclid’s first theorem is an argument The

conclusions in steps 1 to 4 are called intermediate conclusions, while the conclusion in step 5

is the main conclusion

Question: All arguments, or sequences of arguments, are examples of reasoning, but is every

piece of reasoning an argument? A perceptual judgment such as "I see a blue square", or the conclusions of scientific experts reading in X-rays, or looking through a microscope, may be examples of reasoning that are not arguments They are derived from what Kuhn called tacit knowledge, acquired through training and experience (e.g., knowing how to ride a bicycle) It

is not easily articulated, and is not stated in any language

The Difference between Good and Bad Arguments

In logic, we assume that any reasoning is represented as an argument, and the evaluation of

an argument involves two questions:

1 Are the premises true?

2 Supposing that the premises are true, what sort of support do they give the conclusion?

Answers to question 2: Compare the following arguments

1 All planets move on ellipses Pluto is a planet Therefore, Pluto moves on an ellipse

2 Mercury moves on an ellipse Venus moves on an ellipse Earth moves on an ellipse Mars moves on an ellipse Jupiter moves on an ellipse Saturn moves on an ellipse

Uranus moves on an ellipse Neptune moves on an ellipse Therefore, Pluto moves on

an ellipse

Definition: An argument is deductively valid if and only if it is impossible that its conclusion is false while its premises are true

Examples: Argument 1 is deductively valid, while argument 2 is not

Remark on terminology: The notion of deductively validity is such a central and important

concept in philosophy, that is goes by several names When an argument is deductively valid,

we say that the conclusion follows from the premises, or the conclusion is deduced from, or inferred from, or proved from the premises Or we may say that the premises imply, or entail,

or prove the conclusion We also talk of deductively valid arguments as being demonstrative All these different terms mean exactly the same thing, so the situation is far simpler than it appears

What’s possible? The sense of "impossible" needs clarification Consider the example:

3 George is a human being George is 100 years old George has arthritis Therefore, George will not run a four-minute mile tomorrow

Suppose that the premises are true In logic, it is possible that George will run a four-minute mile tomorrow It is not physically possible But logicians have a far more liberal sense of what

is "possible" in mind in their definition of deductive validity Argument 3 is not deductively valid on their definition So, argument 3 is invalid

Key idea: In any deductively valid argument, there is a sense in which the conclusion is

contained in premises Deductive reasoning serves the purpose of extracting information from the premises In a non-deductive argument, the conclusion ‘goes beyond’ the premises

Inferences in which the conclusion amplifies the premises is sometimes called ampliative

inference

Therefore, whether an argument is deductively valid or not, depends on what the premises

are

‘Missing’ premises?: We can always add a premise to turn an invalid argument into a valid

argument For example, if we add the premise "No 100-year-old human being with arthritis will run a four-minute mile tomorrow" to argument 3, then the new argument is deductively valid (The original argument, of course, is still invalid)

Definition: An argument is inductively strong if and only if it is improbable that its conclusion

is false while its premises are true

Remember: This definition is the same as the definition of "deductively valid" except that

"impossible" is replaced by "improbable."

The degree of strength of an inductive argument may be measured by the probability of that the conclusion is true given that all the premises are true

The probability of the conclusion of a deductively valid argument given the premises is one, so deductively valid arguments may be thought of as the limiting case of a strong inductive

arguments Ampliative arguments have an inductive strength less than one

The probability of the conclusion given the premises can change from person to person, as it depends on the stock of relevant knowledge possessed by a given person at a given time

Summary: In response to question 2, we may give answers like "the argument is valid", "the

arguments is inductively strong" or "the argument is inductively weak."

Exercise: Discuss the following examples (all statements are understood to refer to the year

1998):

4 There are multi-celled organisms living on Mars Therefore, there is intelligent life on

5 There are multi-celled organisms living on Mars Therefore, there are single-celled organisms living on Mars

6 There are multi-celled organisms living in Lake Mendota Therefore, there is

intelligent life living in Lake Mendota

7 There are multi-celled organisms living in Lake Mendota Therefore, there are celled organisms living in Lake Mendota

single-Nevertheless, in logic, it is assumed that the answer to question 1 is relevant to the evaluation

of an argument But it is a question that needs to be asked in addition to question 2 So, if the premises of an inductively strong argument are false, then logicians are forced to say that the argument is not a good one It is confusing to say that an inductively strong argument is a weak argument, but this is how the terms are defined

Tip: Defined terms must be used as defined You can’t use the term differently just because

you don’t agree with the definition

Different Kinds of Ampliative Argument

Definition: Any argument that is not deductively valid, or deductively invalid, is called an

ampliative argument The term refers to the fact that the conclusion of such argument goes beyond, or amplifies upon, the premises

Remark on terminology: Again the notion of ‘invalid’ is so common and central, that it goes

by many names Other terms commonly used are inductive and non-demonstrative I prefer

‘ampliative’ because it reminds us that the conclusion ‘goes beyond’ the premises, and it does not have the bad reputation that sometimes goes along with the word ‘induction.’

Here are a variety of examples of ampliative arguments:

Simple enumerative induction goes from a list of observations of the form "this A is a B"

to the conclusion "All A’s are B’s" The example Hume made famous is like this:

8 Billiard ball 1 moves when struck Billiard ball 2 moves when struck Billiard ball 3 moves when struck… Billiard ball 100 moves when struck Therefore, all billiard balls move when struck

Some ampliative arguments go from general statements to general statements:

9 All bodies freely falling near the surface of the Earth obey Galileo’s law All planets obey Kepler’s laws Therefore, all material objects obey Newton’s laws.

Others go from general statements to specific statements:

10 All emeralds previously found have been green Therefore, the next emerald to be found will be green

Conclusion: To understand empirical science we need to understand ampliative inference Two Kinds of Science? A Priori and Empirical?

1 A priori science, like Euclid’s geometry, is where the conclusions are deduced from premises that appear to be self-evidently true

2 In empirical science, like physics, conclusions are based on observational data

● This is similar to the distinction between pure mathematics and applied mathematics The distinction is not always sharp

Ever since Einstein rejected the use of Euclidean geometry in his new physics at the turn of the 20th century, it seems that a priori sciences cannot tell us anything about the real world The focus of recent philosophy of science is on the empirical sciences

● A priori sciences contain the strongest form of reasoning, at the expense of telling us less about the real world

Introduction to the Demarcation Problem

Definition: In philosophy of science, we refer to what we already know directly through

observation as the empirical evidence (we are open-minded about the possibility that some of these ‘facts’ are mistaken) See Exercise 1

All of empirical science uses ampliative arguments Hume made the same point in a different way He pointed that in example 8, it is possible that the premises are true and the conclusion

is false No matter how many instances of a generalization we observe, it does not prove that the generalization is true

What is the difference between science and pseudoscience? You often hear that

science is based on the ‘facts’ while pseudoscience is not Or you say that religious belief is based on faith, whereas scientific belief is not Unfortunately, both scientific and non-scientific reasoning go beyond the facts So, can we tell them apart?

Argument:

1 The demarcation between science and pseudoscience depends only the nature of the reasoning used

2 Genuine science involves ampliative inference

3 Pseudoscience involves ampliative inference

4 Therefore, there is no demarcation between science and pseudoscience

The problem of demarcation is to say what is wrong with this argument (Question: what are the two things that can be wrong with an argument?)

Review of Central Definitions and Remarks on Terminology

Definition: An argument is deductively valid if and only if it is impossible that its conclusion is false while its premises are true

Remark: The notion of deductively validity is such a central and important concept in

philosophy, that is goes by several names When an argument is deductively valid, we say that the conclusion follows from the premises, or the conclusion is deduced from, or inferred from,

or proved from the premises Or we may say that the premises imply, or entail, or prove the conclusion We also talk of deductively valid arguments as being demonstrative All these

different terms mean exactly the same thing, so the situation is far simpler than it appears

Definition: Any argument that is not deductively valid, or deductively invalid, is an ampliative argument The term refers to the fact that the conclusion of such argument goes beyond, or amplifies upon, the premises

Remark: Again the notion of ‘invalid’ is so common and central, that it goes by many names

Other terms commonly used are inductive and non-demonstrative I prefer ‘ampliative’

because it reminds us that the conclusion ‘goes beyond’ the premises, and it does not have the bad reputation that sometimes goes along with the word ‘induction.’

Demarcation: Popper, Kuhn and Lakatos

Last modified on Friday, September 18, 1998  Malcolm R Forster, 1998

The Problem

The difference between science and non-science has practical ramifications for society:

● Parapsychology includes the study of such alleged phenomena as telepathy,

clairvoyance, and precognition In 1969 the American Association for the Advancement

of Science (AAAS) admitted the Parapsychology association as an Affiliate member Should they have done that?

● In Arkansas, U S A., there were attempts to have the biblical story of creation taught

in schools alongside evolutionary theory (after earlier attempts to ban evolutionary

theory failed) They argued that creationism is a just as much a science, and therefore deserves equal time

● The Merriam-Webster's Collegiate® Dictionary defines creation science n (1979):

creationism; also: scientific evidence or arguments put forth in support of creationism Should an authoritative dictionary presuppose that creationism is a science?

● Freudian psychology has a poor reputation in scientific circles Is it a pseudoscience?

● Immanuel Velikovsky and Erich van Daniken wrote best sellers Worlds in Collision and Chariots of the Gods, which angered many scientists Are these examples of

pseudoscience

● Thor Heyerdahl launched the Kon-Tiki expedition to support his theory that the

polynesians migrated from South America Was he a pseudoscientist?

● Gould wrote a book called The Mismeasure of Man about the IQ debate, and

phrenology, which purported to predict the criminal nature of people from their skull shape and other characteristics

● IQ testing has been used to screen children from entering high school, or college, in many countries for many years Does it predict future academic performance reliably? Is there really such a thing as intelligence?

● Chemistry grew out of alchemy One’s a science and the other is not What’s the

difference?

● The label 'science' carries a high degree of authority, and people need to understand when the label, and the authority, are deserved Is there any clear difference between

an unscientific study and a scientific one?

● More generally, an understanding of what science is carries us a step closer to telling the difference between good and bad science, and the limits of good science If we understand how science works, we can be better and more informed use of scientific expertise

If we wanted to know which subjects were generally accepted as science, we would probably find a fairly sharp and clear division between two categories But we are interested in more than that! We want to understand the general characteristics of science that are different from pseudoscience That is actually surprisingly difficult and controversial.

Exercise: Critically evaluate the following characterization of science (from the Encyclopedia Britannica): any system of knowledge that is concerned with the physical world and its

phenomena and that entails unbiased observations and systematic experimentation In

general, a science involves a pursuit of knowledge covering general truths or the operations

of fundamental laws

Examples of Science and Pseudoscience

The key to understanding Popper's demarcation criterion is to compare two examples The first, Popper thinks is typical of science, while the second is typical of pseudoscience

Example (a): Einstein's prediction of the bending of star light For over 200 years prior to

Einstein, Newtonian physics had enjoyed a period of unprecedented success in science Many scientists thought that Newton's theory was the end of science, and many philosophers not only believed that Newton's theory was true, they thought that it was necessarily true They sought to explain why Newton's theory had to be true All that began to change with Planck's

1900 introduction of the idea that energy comes in small discrete packages (the quantum hypothesis) and Einstein's discovery of the special theory of relativity in 1905 Einstein's

special theory of relativity was a way of reconciling some inconsistencies between the wave theory of light and Newtonian mechanics Instead of modifying the wave theory, he modified some of the fundamental assumptions used in Newtonian physics (like the assumption that simultaneity did not depend on a frame of reference, and that the mass does not depend on its velocity) However, Einstein's special theory of relativity said nothing about gravity

Einstein's general theory of relativity was his theory of gravitation, which he had published by

1916 Many scientists were impressed by the aesthetic beauty of Einstein's principles, but it was also important that it be tested by observation For most everyday phenomena, in which velocities are far smaller than the speed of light, there is no detectable difference between Einstein's prediction and Newton's prediction What we needed was a crucial experiment in which Einstein and Newton made different predictions In 1916, there were successful tests of Einstein's special theory But crucial tests of the general theory were harder to come by One such case was provided by the bending of starlight by the gravity of the sun The period from

1900 to at least 1916 was a period of revolution in physics, and Eddington's confirmation of Einstein's prediction in 1919 helped to complete the change in physics

"The idea that light should be deflected by passing close to a massive body had been

suggested by the British astronomer and geologist John Michell in the 18th century However, Einstein's general relativity theory predicted twice as much deflection as Newtonian physics

Quick confirmation of Einstein's result came from measuring the direction of a star close to the

Sun during an expedition led by the British astronomer Sir Arthur Stanley Eddington to observe

the solar eclipse of 1919 Optical determinations of the change of direction of a star are

subject to many systematic errors, and far better confirmation of Einstein's general relativity theory has been obtained from measurements of a closely related effect namely, the increase

of the time taken by electromagnetic radiation along a path close to a massive

body." (Encyclopedia Britannica)

"The theories involved here were Einstein's general theory of relativity and the Newtonian particle theory of light, which predicted only half the relativistic effect The conclusion of this exceedingly difficult measurement that Einstein's theory was followed within the experimental limits of error, which amounted to +/-30 percent was the signal for worldwide feting of

Einstein If his theory had not appealed aesthetically to those able to appreciate it and if there had been any passionate adherents to the Newtonian view, the scope for error could well have been made the excuse for a long drawn-out struggle, especially since several repetitions at subsequent eclipses did little to improve the accuracy In this case, then, the desire to believe was easily satisfied It is gratifying to note that recent advances in radio astronomy have

allowed much greater accuracy to be achieved, and Einstein's prediction is now verified within about 1 percent." (Encyclopedia Britannica)

"According to this theory the deflection, which causes the image of a star to appear slightly too far from the Sun's image, amounts to 1.75 seconds of arc at the limb of the Sun and

decreases in proportion to the apparent distance from the centre of the solar disk of the star whose light is deflected This is twice the amount given by the older Newtonian dynamics if light is assumed to have inertial properties If light does not have such properties, as is

generally accepted now, the Newtonian deflection is zero." (Encyclopedia Britannica)

Reconstruction of the example: Philosophers need a general characterization of the

example: Let E be a statement of the prediction made by Einstein's theory E states the

direction that the starlight will be observed at the time at which the star was to be observed

by Eddington Let T be a statement of the general principled in Einstein's general theory of relativity Let A be the conjunction of all auxiliary statements used to derive, or deduce, E from

T That is to say, the argument with T and A as premises, and E as the conclusion, is

deductively valid Symbolically, we may write this as:

T & A ⇒ E

A will include assumptions like "the sun is spherical ball of mass M", "there are no other bodies close by to add to the sun's gravitational field," "If the sun were not present, then the star would be seen in the direction such-and-such," "the effect of stellar aberration on the direction

of light is such-and-such," and so on

Example (b): Adler's 'individual psychology' Compare the following two (hypothetical)

explanations of human behavior (1) E1: A man pushes a child into the water with the

intention of drowning it (2) E2: A man sacrifices his life in an attempt to save the child

Popper claims that Adler's 'individual psychology' can explain both of these behaviors with equal ease Let T be Adler's theory, let A be the auxiliary assumption that the man suffered feelings of inferiority (producing the need to prove to himself that he dared to commit some crime) Then T & A1 ⇒ E1 Let A2 be the auxiliary assumption that the man suffered feelings

of inferiority (producing the need to prove to himself that he dared to rescue the child) Now T

& A2 ⇒ E2

Definition: Let us say that a theory T predicts an event E if and only if there are auxiliary assumptions that have either been used successfully in other predictions, or are the simplest and most obvious assumptions that one would make in the situation, and that T & A ⇒ E If there exists auxiliary assumptions such that T & A ⇒ E, where A is some ad hoc assumption that is introduced in light of the evidence E itself, then theory T merely accommodates E

In example (a), Einstein's theory predicts the observational evidence, while in example (b), the theory is merely accommodates the evidence

Popper describes the difference by claiming that Einstein's theory is falsifiable, whereas Adler's theory is not

Remark: Popper also claims that the problem with Adler's theory is that it is too easily

verified: "the world was full of verifications of the theory." Adler may have seen it like that, but was he right? My feeling is that mere accommodations do not count as verifications at all Hence, I think that a verificationist could account for the difference between these two

examples as well as, if not better than, a falsificationist

Discussion Question: How does our previous distinction between ampliative inference and

deductive inference enter into these examples, if at all Popperians tend to think that there is

no need for ampliative inference in science at all Why might they think that? Are they right?

Popper's Path to his Demarcation Criteria

(Curd and Cover, pages 1-10) To understand a philosophical theory, like Popper's demarcation criterion, it is useful to see why simpler alternative proposals do not work

Proposal 1: Science is distinguished by its empirical method That is, science is distinguished

from pseudoscience by its use of observational data in making predictions

Objection: Astrology appeals to observation, but is not a science.

Proposal 2: Scientific theories, like Einstein's, are more precise in their predictions that

Adler's psychology, or astrology

Objection: While it is true that pseudosciences do often protect themselves from refutation

by making vague or ambiguous predictions, that is not always the case The 'predictions' of example (b) are precise enough for the purpose, and Einstein's prediction was not exact—it had to allow for many errors of observation

Proposal 3: Science is explanatory, whereas pseudoscience is not

Objection: If you buy into the auxiliary assumptions in Adler's psychology, then the theory

explains the phenomena perfectly well It is true we have little reason to believe that the

explanation is correct, but that is a different issue

Proposal 4: Science is distinguished from pseudoscience by its verifications, or confirmation.

Objection: Popper's objection is that "The world was full of verifications of those theories." I

have remarked that that does not ring true in examples (a) and (b) Nevertheless, there

seems to be some force behind Popper's point in other examples For example, Einstein could have pointed to all the verifications of Newton's theory for low velocities and claim these as verifications for his own theory Yet he did not Why not? Because, says Popper, these were not risky predictions They were not potential falsifiers of Einstein's theory

Popper’s Proposal: Every ‘good’ scientific theory is a prohibition: it forbids certain things to

happen The criterion of the scientific status of a theory is its falsifiability, or refutability, or testability

Note: Popper also anticipates a major objection to his criterion: namely, that any scientific theory can be protected from refutation by introducing ad hoc auxiliary assumptions His reply

is that the very use of ad hoc assumptions, in reducing the falsifiability of theory, also

diminishes its scientific status The problem with Popper’s reply is that it is not always, if ever, clear in advance that ad hoc auxiliary assumptions are needed to save the theory This is

essentially Kuhn’s point

psychology, which has nothing to do with the status of the theory as scientific There are no scientific or unscientific ways of inventing theories They can come in a dream or they can be constructed from the data—it does not matter Rather, the essence of science is about how predictions are deduced from the theories This way of viewing science is known as

hypothetico-deductivism The difference between science and pseudoscience rests solely on the 'deductive' part of the process

Kuhn ’s Characterization of Science

Thomas Kuhn makes the following points against Popper (Curd and Cover, pages 11-19):

● The kind of examples Popper considers, like the 1919 test of Einstein’s theory of

gravitation, is an example of extraordinary science, or revolutionary science These are relatively rare in science

● In non-revolutionary science, or normal science, the aim of research is to connect the experimental data to the background theory, by inventing the appropriate auxiliary

assumptions If a scientist fails, then scientist’s lack of ingenuity is blamed, not the

theory

● It is for normal, not extraordinary, science that scientists are trained, and

● "If a demarcation criterion exists , it may lie in that part of science which Sir Karl

ignores."

Question: Kuhn concedes that "There is one sort of 'statement' or 'hypothesis' that scientists

do repeatedly subject to systematic test I have in mind statements of an individual’s guesses about the proper way to connect his own research problem with the corpus of accepted

scientific knowledge." Thus, thinks (a) a demarcation criterion should refer to normal science, and (b) falsifiability does play a role in normal science So, why doesn’t he apply a falsifiability criterion to normal science, and say that an alleged science is genuinely scientific if and only if its solutions to puzzles are falsifiable? As Kuhn says, this is not what Popper has in mind But does the new criterion work?

Central Concepts in Kuhn’s Account of Revolutionary Change in Science: Kuhn denies

that theories change by falsification in science, but he does not deny that theories are

sometimes replaced (revised) What is his own account of ‘theory replacement’? Here is very brief summary of his positive account:

1 The process by which one paradigm is replaced by another is called revolutionary

another

4 A paradigm is overthrown only if the paradigm is in crisis and there is a second

paradigm that shows equal or greater puzzle-solving potential

Kuhn’s Demarcation Criterion: All of genuine science has a puzzle-solving tradition, while

pseudosciences do not

Objection: Until Kuhn says what a puzzle-solving tradition is, his criterion is rather vague

Why wouldn’t a research tradition that sought worked backwards from the fact to the auxiliary hypotheses count as puzzle-solving It seems that Kuhn needs to add something like

falsifiability

Kuhn on Astrology:

1 Kuhn agrees that astrology is pseudoscience, but makes the point that it was not

obvious that it was pseudoscience in the century it was practiced most That is because its auxiliary assumptions, based on the configuration of the planets at the time of birth, were subject to genuine doubt Not everyone was sure of their exact date of birth in any case The problem is that similar arguments explaining away failed predictions are regularly used today in medicine or meteorology

2 Astrology has no science to practice because practitioners had rules to apply, but no puzzles to solve Most difficulties "were beyond the astrologer’s knowledge, control, and responsibility." In astronomy, however, if a prediction failed, a scientist "could hope to set the situation right." There was a puzzle-solving tradition

Final argument:

● For a long period of time, there was a sense in which Ptolemaic astronomy was

unfalsifiable by the means available (naked-eye observations) But that did not stop it from being science at the time Moreover, when it was finally falsified (by Galileo’s

observation of the phases of Venus, the moon’s of Jupiter, and Brahe’s observations of comets), it had already been rejected

Necessary and Sufficient Conditions

necessary condition: E.g., being enrolled in this course is a necessary condition for you

getting an A for the course That is, you will not get an A if you are not registered Or

equivalently, if you do get an A, then you are registered In general: A necessary condition for

an event or state of affairs X is one that has to hold for X to be true A necessary condition is contrasted with a sufficient condition

sufficient condition: E.g., getting an A in this course is a sufficient condition for passing this

course That is, it you get an A then you will pass In general: A sufficient condition for an event, or state of affairs X is one that enough to makes X true.

necessary and sufficient condition: A condition is necessary and sufficient for a

statement, or event, X if and only if it is necessary for X and sufficient for X It is often

expressed by the phrase ‘if and only if’ or the abbreviation ‘iff’ E.g., a necessary and sufficient condition for passing this course is to receive a passing grade while being registered for the course

Popper says that the falsifiability is a necessary and sufficient condition for genuine science

● Falsifiability is not a sufficient condition because astrology is falsifiable but not a

science In the 1960s, Michael Gauquelin examined the careers and times of birth of 25,000 Frenchmen, and found no significant correlation between careers and either sun sign, moon sign, or ascendant sign (see the Thagard reading) Gauquelin found some statistically significant correlations between certain occupations and the positions of certain planets at the time of their birth, but we can expect 1 in 20 random associations will be statistically significant by chance alone Also, studies of twin do not show the correlation one would expect These results cannot be explained away by supposing that almost all assumptions in every case were false Therefore, such a study falsifies astrology in a sense that Popper would accept, and these studies were always possible, which proves that astrology was always falsifiable

● Falsifiability is not necessary for science The example of Ptolemaic astronomy shows this, because prior to the invention of telescope it was not falsifiable but it was still a science

Counterexamples: In order to show that a condition is not a sufficient condition for X, we

only need an example in which the condition holds, but X does not In order to show that a condition is not a necessary condition for X, we only need an example in which X holds but the condition does not In each case, the examples are called counterexamples Astrology is a counterexample for the sufficiency of falsifiability for science, and Ptolemaic astronomy is

counterexample to its necessity

Here are some other arguments that make use of counterexamples

● Astrology is not a science because it has mystical origins Counterexample: Chemistry

had its origins in alchemy and medicine had occult beginnings

● Astrology is not a science because people believe astrology for irrational reasons

Counterexample: Many people believe in Einstein's theories for irrational reasons

● Astrology is not a science because it assumes that gravitational influences of the planets

influence us, but they are too weak to do that Counterexamples: The lack of a

physical foundation did not stop geologists from believing in continental drift, and we

have plenty of evidence to prove that smoking causes lung cancer with knowing the details of the carcinogenesis

Lakatos's Methodology of Scientific Research Programs

Last modified on Thursday, September 24, 1998, by Malcolm R Forster

Points of Disagreement between Lakatos and Kuhn

1 Subjective or objective? Kuhn’s demarcation criterion appears to be subjective it

depends on what scientists do and what they believe (their psychology) In contrast, Lakatos insists that "a statement may be pseudoscientific even if it is eminently

‘plausible’ and everyone believes in it." Belief that earth is flat may count as an example

of that And "it may be scientifically valuable even if it is unbelievable and nobody

believes in it." Copernicus's theory that the sun moves like that, and very few believed

in evolution when Darwin introduced his theory

2 Sociology or logic? Another point of disagreement between Kuhn and Lakatos is

whether a demarcation criterion should be talking about which statements are scientific

or pseudoscientific, or whether it should be saying which community is scientific or

unscientific Lakatos, as a neo-Popperian, was raised in the tradition in which logic was the main tool in philosophy of science, whereas Kuhn is more interested in the sociology

of science

3 Religion or Science? Kuhn compares science to religion, but Lakatos rejects this

comparison

Main Point of Agreement between Lakatos and Kuhn

Any good science can be practiced in a pseudoscientific way The demarcation between

science and pseudoscience refers to its method and not just what the theory says (its content)

● For example, some evolutionists may be tempted to fill in auxiliary assumptions in an ad hoc way by working backwards from what is to be explained For example, if see from the fossil record that horses teeth become elongated, we may be tempted into using evolutionary theory to infer that there was some change in the environment that made shorter teeth less fit, and then explain the change by appealing to the law of natural selection that "only the fittest survive."

● It would be equally easy for Newtonian mechanics to be practiced in a pseudoscientific way After all, Newton’s law of inertia says that a body continues in a straight line with uniform velocity until acted on by a force, and then defines a force as anything that diverts a body from uniform motion in a straight line

Lakatos on Popper ’s Demarcation Criterion

1 Lakatos argues that ‘falsifiable’ already refers to how science is practiced He interprets Popper as demanding that scientists "specify in advance a crucial experiment (or

observation) which can falsify it, and it is pseudoscientific if one refuses to specify such

a ‘potential’ falsifier.’ If so, Popper does not demarcate scientific statements for

pseudoscientific ones, but rather scientific method from non-scientific method."

2 While Popper’s criterion does focus on practice, it is still wrong because it "ignores the remarkable tenacity of theories." Scientists will either invent some rescue hypothesis (accommodate the theory) or ignore the problem and direct their attention to other problems For example, some problems may be too hard (nobody rejected Newtonian mechanics because it couldn’t predict all the properties of turbulent fluid flow, or the chaotic motion of a physical pendulum)

A Puzzle about Prediction

Earlier, we saw that Popper's two examples, Adler's theory at one extreme, and Einstein's theory at the other, illustrated a difference between accommodation and prediction Adler's theory merely accommodated the facts because it worked backwards from the evidence E to the auxiliary assumption A needed so that the theory T entailed E (T & A ⇒ E) At the other extreme, if intellectual honesty requires that a scientist specify a ‘potential’ falsifier’ in

advance, then they must specify A in advance That is a sufficient condition for the theory to make a prediction But is it necessary?

Lakatos ’s Picture of Science

The typical unit of science is not an isolated hypothesis, but rather a research programme, consisting in a hard core (theory), protective belt (auxiliary assumptions) and a heuristic

Lakatos quote: A heuristic is a "powerful problem solving machinery, which with the help of sophisticated mathematical techniques, digests anomalies and even turns them into positive evidence For instance, if a planet does not move exactly as it should, the Newtonian scientist checks his conjectures concerning atmospheric refraction, concerning propagation of light in magnetic storms, and hundreds of other conjectures that are all part of the programme He may even invent a hitherto unknown planet and calculate its position, mass and velocity in order to explain the anomaly." (Lakatos, 1977, p 5)

● In Kuhn's terminology: Heuristics are hints about how to solve normal science puzzles

● In my terms: A heuristic is a hint about how to change the auxiliary assumptions so that the theory better fits the facts

The negative heuristic forbids scientists to question or criticize the hard core of a research programme "The positive heuristic consists of a partially articulated set of suggestions or hints

on how to change, develop the 'refutable variants' of the research programme, how to modify, sophisticate, the 'refutable' protective belt." (Lakatos, 1970, p.135).

Example: Le Verrier and Adams were faced with the following problem in Newton's theory of planetary motion There were discrepancies (unpredicted wobbles) in the motion of the

outermost planet known at the time (Uranus) They postulated that these might be caused by

a hitherto unknown planet Based on that conjecture they recalculated the solutions to

Newton's equations, and fit the solutions to the known data for Uranus That fit even predicted the position of the postulated planet, whereupon Neptune was seen for the first time once telescopes were pointed in that direction (actually, it was later discovered that it had been seen before, but mistaken for a comet)

● In this example, the positive heuristic used was something like this: "If there is an

anomaly in Newton's theory on the assumption that there are n planets, then try

assuming that there are n+1 planets."

The Role of Background Evidence

We have identified auxiliary assumptions with Lakatos's protective belt That is, we are

assuming that auxiliary assumptions are always provisional in some sense However, we must now decide whether to count statements of background evidence, prior observations, and data, as auxiliary assumptions They are auxiliary in the sense that they are needed in order to make predictions In the Le Verrier-Adams example it would be impossible to predict the

position of the postulated planet without making use of the observed positions of Uranus, and the other planets Let use refer to this background data by the letter D ('D' for data) We now replace the previous pattern of inference (T & A ⇒ E) by the pattern:

T & A & D ⇒ E

We still refer to A as the auxiliary assumption, but with the explicit understanding that it

excludes the background observational evidence or data D

Models

It may be useful at this point to introduce the concept of a model A model is theoretical

statement, (often in the form of an equation) usually deduced from a theory with the aid a

auxiliary assumptions That is, a model M is equal to a theory T combined with an auxiliary assumption A (which will be long list of assumptions in most cases) That is, M = T & A

Example: In the LeVerrier-Adams example, there was first a Newtonian model of planetary

motion that assumed that there are only 7 planets There were discrepancies between the

predictions of this model and the observed motions of Uranus Therefore, the model was

replaced by one that assumed the existence of 8 planets Not only did that accommodate the anomalous motion of Uranus, but it predicted position of the eighth planet, whereupon

Neptune was discovered

Remarks:

1 A model M is falsified when M & D ⇒ E because D is not blamed for the failed

prediction Therefore, models are falsifiable, or refutable, even though theories are not

2 The notion of a 'model' corresponds to Lakatos's notion of a 'refutable variant of a

theory' If a Lakatosian heuristic defines an ordered list of auxiliary assumptions, A0, A1,

A2, A3, then it also defines an ordered list of models M0, M1, M2, M3,

3 This use of the term 'model' differs from two other uses that are common in the

philosophy of science (a) A 'model' as in a model airplane Such models do appear in science, such as in the 'model of the DNA molecule' Watson and Crick used, which was made of wooden balls joined with sticks (b) 'Model' in the sense used by

mathematicians in model theory There it has a rather technical meaning, which

corresponds roughly to what logicians call an interpretation of a language (an

assignment of objects to names, set of objects to properties, a set of object pairs to relations, and so on)

4 Scientists use the term 'model' all the time, and it very rarely fits sense (a) and

absolutely never fits sense (b) Our use of the term best fits the standard scientific

usage

Solution to the Puzzle about Prediction

If a heuristics exists, then a scientist has an ordered list of suggested models M0, M1, M2,

M3, Now the theory T is no longer falsifiable in Popper's methodological sense, for if a

scientist tries makes the prediction E0 from model M0 and E0 proves to be false, then the

scientist does not blame T, but instead moves to M1, because it is next on the ordered list, and so on Scientists now predict E1 because M1 & B ⇒ E1 And so on There is no falsifiability

of the theory, but it can still make predictions Thus, the idea of a heuristic may save the

distinction between accommodation and prediction, and thereby providing a weaker sufficient condition for prediction

● Note that the research program makes a different set of predictions at different times This allows Lakatos to introduce the idea of novel predictions new predictions not make before

When Should One Model Supercede Another?

Lakatos does not believe that falsification is important in science, but like Kuhn, he does

recognize that theories, or paradigms, are superceded in science He objects to Kuhn's

description of this process, of scientific revolutions, as being a like a religious conversion, or a social revolution Lakatos things that the process is more objective Here is his view

Thesis: A model M¢ supercedes a model M if and only if (1) M¢ has excess empirical content

over T : that is, it predicts novel facts, that is, facts improbable in light of, or even forbidden

by M; (2) M¢ explains the previous success of M, that is, all the unrefuted content of M is

contained (within the limits of observational error) in the content of M¢ ; and (3) some excess content of M¢ is corroborated (see Lakatos, 1970, p 116; the phrase "should supercede" is

my paraphrase, and I have replaced 'theory' by 'model'.)

● This is Lakatos's account of normal science

Lakatos introduces some new terminology to help formulate his theory of science

1 A problemshift is a series of models M1, M2, such that (i) each can explain the

empirical success of its predecessor, and (ii) each can explain at least some of the

emprical failure of it predecessor as well In other words, a Lakatosian problemshift occurs whenever a Kuhnian solution to a normal science puzzle is found, since to be a solution is must remove the anomaly with creating new one Note that a problemshift does not have to make novel predictions

2 A theoretically progressive problemshift is a problemshift that predicts some novel facts

3 A problemshift is empirically progressive if it is theoretically progressive and some of the novel predictions have been corroborated

Note: In Lakatos's original writings, Lakatos uses the word 'theory' instead of 'model', but

only because he fails to make the distinction I think that he models in mind

Definition: A problemshift is progressive if it is theoretically and empirically progressive

Otherwise the problemshift is degenerating The idea of a degenerating problemshift

corresponds to Kuhn's notion of crisis

Example 1: The LeVerrier-Adams discovery of Neptune is a great example of a problemshift

that was progressive, because (1) it led to novel predictions (the position of Neptune), which (2) were then corroborated

Example 2: Ptolemaic astronomy was degenerating not because it failed to be theoretically

progressive (Ptolemaic astronomers had the option of adding more epicycles) but because it was not empirically progressive That is, adding an epicycle would lead to novel predictions,

but they were not corroborated (confirmed).

Lakatos on Revolutions

What is Lakatos's theory about when one theory should supercede another? In fact, Lakatos does not provide such a criterion Not even when one research program is degenerating and another is progressive does Lakatos say that scientists do or should only work on the

progressive one, because like the stock-market, they may change their status over time

● The methodology of scientific research programmes does not offer instant rationality

It is not irrational for a scientist to work on a young research programme if she thinks it shows potential Nor is it irrational for a scientist to stick with an old programme in the hope of

making it progressive Thus, Lakatos appears to agree with Kuhn that theory change is a

rather fuzzy phenomenon But he does insist that it depends on the assessment of objective facts the future progressiveness or degeneration of research programs The decision of

scientists, however, must rely of their subjective predictions of the future course of science Unlike Kuhn, Lakatos does not think that the uncertainty makes these decisions irrational

Example 3: Prout's program Prout, in 1815, claimed that the atomic weights of all pure

elements were whole numbers He knew that the experimental results known at the time did not confirm his theory, but he thought that this arose because chemical substances as they naturally occurred were impure Thus, there ensued a program of research whereby chemical substances were purified by chemical means This program led from one failure to the next The program at this stage was degenerating However, Rutherford's school explained this failure by the fact that different elements can be chemically identical (as explained by the periodic table) They proposed that the substances should be purified by physical means

(powerful centrifuges), whereupon the program made a progressive shift Lakatos (1970,

pp.138-140) uses this as an example of why it would be wrong to advise scientists to instantly abandon a degenerating research program

Question: We have talked about Lakatos's view of normal science and revolutionary science

However, this is separate from the demarcation issue Popper thinks that the essence of

science lies in the nature of revolutions, but Kuhn thinks that the essence of science lies in the nature of non-revolutionary science Where does Lakatos stand on this issue?

Lakatos's Demarcation Criterion

Lakatos is not explicit about his demarcation criterion in the passage we read, but he is explicit about in his 1970 article: "We 'accept' problemshifts as 'scientific' only if they are at least

theoretically progressive; if they are not, we 'reject' them as 'pseudoscientific.'" (1970, p 118)

Presumably, therefore, a research program is scientific if and only if it is at least theoretically progressive Note that it is possible for a research program to be scientific at one time, but not

at another It is even that a program practiced by one group is scientific, while the practice of another group is pseudoscientific This is how Lakatos is agreeing with Kuhn's point that even

a good theory can always be practiced in a pseudoscientific was Thus, Adler's theory (about inferiority complexes) might potentially be a good theory, but the fact is that it was being practiced in a pseudoscientific way (if Popper's account is correct)

● Lakatos is agreeing with Kuhn, against Popper, that the essence of science lies in the nature of normal science

Example 4: Astrology Astrology has no theoretically progressive problemshifts, and therefore

no empirically progressive problemshifts That is, it made no novel predictions, despite that fact that it made predictions Therefore, astrology was not a science

Example 5: Prout's program While Prout's program was degenerating, it was still

theoretically progressive, and hence scientific

Example 6: Jeane Dixon was a self-proclaimed psychic who predicted that JFK's

assassination She made over 200 predictions each year (most of them wrong of course) Did her method count as scientific? It would be by Popper's criterion, but not by Kuhn's or

Lakatos's demarcation criteria Like astrology, there was no Kuhnian puzzle solving, and no theoretically progressive problemshifts

Musgrave's Criticisms of Lakatos

In an article called "Method or Madness" (in Cohen, R S., Feyerabend, P K and Wartofsky,

M W (eds) Essays in Memory of Irme Lakatos, Dordrecht, Holland, D Reidel), Alan Musgrave (1976) raises some interesting objections to Lakatos's theory of science, which I have

expanded upon in places

1 Is the negative heuristic needed? Before 1850, Newtonian seldom treated Newton's

law of gravitation as part of the hard core Therefore, scientists did not follow Lakatos's methodology and render Newton's laws unfalsifiable by fiat And why should scientists have to specify in advance not to modify or renounce them in the face of difficulties Surely, it is enough that it is harder to produce theoretically problemshifts by changing central assumptions because it is then harder to explain all the successes of the

superceded model But there is no reason to rule it out in advance

2 Are positive heuristics always specified in advance? Where was the positive

heuristic in the example of Prout's program? No-one tried physical separation of

chemical substances as soon as the chemical methods failed They kept trying to

improve the chemical methods It was only after the discovery of chemical similarities

that the hint or suggestion appeared

3 Why not compare one research program against another? Musgrave thinks that

Lakatos is overcautious in not recommending any rule for choice between competing research programs Why not say, that on the whole, the scientific community should devote more resources to progressive as opposed to degenerating research programs?

Evolutionary Theory

Last modified on Friday, October 02, 1998, by Malcolm R Forster

(Extracted in part from "Philosophy of Biology" by James G Lennox)

Fact versus theory:

Fact of evolution = the fact that evolution has occurred

Theory of evolution = an explanation about how and why evolution has occurred

Note: Darwin did help establish the fact of evolution However, the fact of evolution was

already accepted by some prominent biologists prior to Darwin, so this is not his most

important claim to fame

● It is possible to accept the fact of evolution, but to seriously disagree with (or even misunderstand) Darwin’s theory of how the fact of evolution come about

Darwin’s theory of evolution is roughly as follows:

1 The struggle for survival: Biological organisms have more offspring than can possibly

survive

2 Inheritability: Biological organisms inherit some of their traits from their ancestors

and pass them on to their descendents

3 Variation: The inheritable traits of biological organisms vary, even within the same

species

4 Differential fitness: Some inheritable traits will be more advantageous than others in

the struggle for survival

Therefore, there has been and will continue to be, on average, a (natural) selection of those

organisms that have advantageous traits that will lead to the evolution of species

This is what Lakatos would call the hard core of Darwin’s research program.

The radical nature of Darwin’s theory

The fact of evolution is radical enough, especially in light of the extremely recent arrival of homo sapiens It questions the primacy of our place of the universe However, the Darwin’s theory is even more radical than that Darwin delayed publication of his theory for many

years; in fact he only published when he discovered that Wallace was about to publish the

same theory The probable reason for his delay was a fear of the controversy his theory would provoke

1 Darwin’s theory undermines one of best theological arguments for the

existence of God: If you come across a watch, and observed its intricate design, then

it is reasonable to infer the existence of a watchmaker If you come across a biological organism that has an even more intricate design, then it is reasonable to infer the

existence of a Creator This is called the argument from design Evolutionary theory

provides an alternative explanation Moreover, the imperfection of many designs is

evidence for evolution and against design

2 Darwin’s theory does not imply that evolution is progressive Evolution has no

predetermined direction The direction of evolutionary change depends on the local environment at the time There is no progression from inferior to superior organisms implied by the theory In fact, immoral traits like ruthlessness and violence are often rewarded in evolution In particular, there is no implication that homo sapiens is

superior to other species There is no final cause directing evolutionary change

Evolution is not teleological or goal directed

3 Darwin’s theory supports a materialistic world view (nothing to do with

materialism in the consumer sense) The view that humans have souls, while animals do not, finds no place in Darwin’s theory It supports the view that the only things in the universe are material things

The protective belt: Darwin’s theory predicts (or postdicts) that evolution has occurred

However, the theory, by itself, does not say which traits are inheritable, nor how they vary, or the way in which resources are limited, or how the different traits aid in survival, or how all these factors change over time

A model of a particular episode or instance of evolutionary change will add specific details to the hard core assumptions, concerning:

a the range of inheritable traits in a biological population(s)

b the environment, and how it changes over time

c the relative benefit that these traits confer to the members of the populations

possessing them in the various environments (fitness values)

Accommodation versus prediction: Some of these details may be introduced as

parameters (e.g., fitness parameters), which are inferred backwards from facts to be

explained But if all of these details are inferred from the facts to be explained, then the

theory is merely accommodating the facts, and there are no predictions (or postdictions) In that case, evolutionary theory would be pseudoscientific according to Lakatos’s demarcation criterion

The positive heuristic, if it exists, should suggest how these details should be filled in

should the most plausible assumption fail to accommodate the observational facts

Definition: A homology is a similarity between or amongst different species that is the result

of their common ancestry There are at least 3 kinds of homologies: (a) Structural homologies such as the similarity between the bone structure in a bat’s wing and our forearm (b)

Behavioral homologies arising for instincts inherited from a common ancestor (c) Protein homologies in which the sequences of amino acids that for a protein are similar because of common ancestry Similarities that do not arise from common ancestry, such as the wing of a bird and the wing of an insect, are called analogies

Kinds of evidence for evolution:

1 The fossil record The facts of evolution, or the story of evolution has been pieced

together mainly from the fossil record Example 1 is an example of Darwin’s theory may explain such evidence

2 Homologies in living species If we look carefully at living species we see surprising

and unexpected similarities (Lakatos’s novel facts?) between disparate species These may range from similar bone structures in limbs of whales and bears, to similarities of the instinctive behavior of water fowl living in quite different areas of the globe, to

similarities and differences in protein sequences in living organisms

3 Artificial selection Breeding experiments that show that selection can transform a

population from one kind to another This provides limited support for inheritability and variation It does not provide evidence for the other postulates

4 Experimental evidence from genetics There is now a lot of biochemical evidence

about DNA and the mechanisms of inheritance This helps provide auxiliary hypotheses about the source of inheritable variation, and the mechanisms of inheritance For

example, it could help support Assumption 3 in Example 1

Let's at an example of evolutionary explanation

Example 1: The evolution of horses

● Fact to be explained: In the lineage leading up to the modern genus Equus, of which the horse is a species, the fossil record shows that the ratio of molar tooth height to length increases over time, and that there is an acceleration in the rate of change

through time

● Assumption 1: The environment changed In the Miocene period, Merychippus and its descendents abandoned the habit common to all earlier horses of browsing on leaves, and took the newly evolved grasses as their main food

Support: There is independent fossil evidence confirming that grasses evolved and

become abundant at that time.

● Assumption 2: Engineering assumption The high silicate content of grasses makes for increased wear per unit of vegetation consumed

Support: Look at modern species and assume that the same physical facts apply for all

time Also note that there was another horse lineage which continued to grace on

leaves and did not evolve an elongated tooth

● Assumption 3: Adaptationist assumption Height to length ratio of teeth varied in

horse populations, and was an inheritable trait

Support: Look at modern horse species to check for variation and check for

inheritability through artificial breeding experiments

● Assumption 4: Resource assumption There were greater food resources available per individual for those horses able to grace on the newly evolved grasses

Support: It is almost a matter of logic to say that a horse that can eat leaves or grass

has more food available to it than a horse that can only eat leaves

● Assumption 5: Co-evolution assumption Grass continued to be a viable food resource despite the grazing of the new horse species That is, the grasses managed to survive this grazing assault

Support: Look at fossil evidence for grasses; compare "grazability" of modern grasses Remarks:

1 It is very hard to think of all the auxiliary assumptions need to deductively entail the fact to be explained

2 Most of the assumptions have independent sources of support It will not matter if some

of the assumptions have no independent support, since some degree of accommodation

is allowed

3 Some of the assumptions talk about other instances of evolution Does this beg the question? No, at worst it shows that the explanations need to be evaluated as a whole That is why Darwin's Origin was convincing in a way that previous arguments for

evolution were not it tied together many different explanations that appealed to the same core assumptions

4 What matters is that various facts are tied together in a surprisingly tidy way, which is hard to explain as "arising from chance"

Figure 1: Phylogeny based on differences in the protein sequence of

cytochrome c in organisms ranging from Neurospora mold to humans

"The Theory of Evolution: Patterns and rates of species evolution: MOLECULAR EVOLUTION: The molecular clock of evolution." Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=macro/5002/24/53.html>

Figure 2: Rate of nucleotide substitution over paleontological time Each dot marks

(1) the point at which a pair of species diverged from a common ancestor and (2) the number of nucleotide substitutions, or protein changes, that have occurred since the divergence The solid line drawn from the origin to the outermost dot gives the

average rate of substitution

From F.J Ayala, E McMullin (ed.), Evolution and Creation (1985)

"The Theory of Evolution: Patterns and rates of species evolution: MOLECULAR

EVOLUTION: The molecular clock of evolution." Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=macro/5002/24/53.html>

VESTIGES OF EVOLUTION: "Human and other nonaquatic embryos exhibit gill slits even

though they never breathe through gills These slits are found in the embryos of all

vertebrates because they share as common ancestors the fish in which these structures first evolved Human embryos also exhibit by the fourth week of development a well-defined tail, which reaches maximum length when the embryo is six weeks old Similar embryonic tails are found in other mammals, such as dogs, horses, and monkeys; in humans, however, the tail eventually shortens, persisting only as a rudiment in the adult coccyx."

"The Theory of Evolution: The evidence for evolution: EMBRYONIC DEVELOPMENT AND

VESTIGES" Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=macro/5002/24/9.html>

BIOGEOGRAPHY: "Darwin also saw a confirmation of evolution in the geographic distribution

of plants and animals, and later knowledge has reinforced his observations For example,

there are about 1,500 species of Drosophila vinegar flies in the world; nearly one-third of them live in Hawaii and nowhere else, although the total area of the archipelago is less than one-twentieth the area of California There are also in Hawaii more than 1,000 species of snails and other land mollusks that exist nowhere else This unusual diversity is easily explained by evolution The Hawaiian Islands are extremely isolated and have had few colonizers; those species that arrived there found many unoccupied ecological niches, or local environments suited to sustain them and lacking predators that would prevent them from multiplying In response, they rapidly diversified; this process of diversifying in order to fill in ecological niches

is called adaptive radiation."

"The Theory of Evolution: The evidence for evolution: BIOGEOGRAPHY" Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=macro/5002/24/10.html>

MOLECULAR EVOLUTION: A remarkable uniformity exists in the molecular components of

organisms in the nature of the components as well as in the ways in which they are

assembled and used In all bacteria, plants, animals, and humans, the DNA comprises a

different sequence of the same four component nucleotides, and all of the various proteins are synthesized from different combinations and sequences of the same 20 amino acids, although several hundred other amino acids do exist The genetic "code" by which the information

contained in the nuclear DNA is passed on to proteins is everywhere the same Similar

metabolic pathways are used by the most diverse organisms to produce energy and to make

up the cell components

This unity reveals the genetic continuity and common ancestry of all organisms There is no other rational way to account for their molecular uniformity when numerous alternative

structures are equally likely The genetic code may serve as an example Each particular

sequence of three nucleotides in the nuclear DNA acts as a pattern, or code, for the

production of exactly the same amino acid in all organisms This is no more necessary than it

is for a language to use a particular combination of letters to represent a particular reality If it

is found that certain sequences of letters planet, tree, woman are used with identical

meanings in a number of different books, one can be sure that the languages used in those books are of common origin

Genes and proteins are long molecules that contain information in the sequence of their

components in much the same way as sentences of the English language contain information

in the sequence of their letters and words The sequences that make up the genes are passed

on from parents to offspring, identical except for occasional changes introduced by mutations

To illustrate, assume that two books are being compared; both books are 200 pages long and contain the same number of chapters Closer examination reveals that the two books are

identical page for page and word for word, except that an occasional word say one in 100 is different The two books cannot have been written independently; either one has been copied from the other or both have been copied, directly or indirectly, from the same original book Similarly, if each nucleotide is represented by one letter, the complete sequence of nucleotides

in the DNA of a higher organism would require several hundred books of hundreds of pages, with several thousand letters on each page When the "pages" (or sequence of nucleotides) in these "books" (organisms) are examined one by one, the correspondence in the

"letters" (nucleotides) gives unmistakable evidence of common origin

The arguments presented above are based on different grounds, although both attest to

evolution Using the alphabet analogy, the first argument says that languages that use the same dictionary the same genetic code and the same 20 amino acids cannot be of

independent origin The second argument, concerning similarity in the sequence of nucleotides

in the DNA or the sequence of amino acids in the proteins, says that books with very similar texts cannot be of independent origin

The evidence of evolution revealed by molecular biology goes one step further The degree of similarity in the sequence of nucleotides or of amino acids can be precisely quantified For example, cytochrome c (a protein molecule) of humans and chimpanzees consists of the same

104 amino acids in exactly the same order; but differs from that of rhesus monkeys by one amino acid, that of horses by 11 additional amino acids, and that of tuna by 21 additional amino acids The degree of similarity reflects the recency of common ancestry Thus, the

inferences from comparative anatomy and other disciplines concerning evolutionary history can be tested in molecular studies of DNA and proteins by examining their sequences of

nucleotides and amino acids

The authority of this kind of test is overwhelming; each of the thousands of genes and

thousands of proteins contained in an organism provides an independent test of that

organism's evolutionary history Not all possible tests have been performed, but many

hundreds have been done, and not one has given evidence contrary to evolution There is probably no other notion in any field of science that has been as extensively tested and as thoroughly corroborated as the evolutionary origin of living organisms

"The Theory of Evolution: The evidence for evolution: MOLECULAR BIOLOGY" Britannica

Online <http://www.eb.com:180/cgi-bin/g?DocF=macro/5002/24/11.html>

Homology, in biology, similarity of the structure, physiology, or development of different

species of organisms based upon their descent from a common evolutionary ancestor

Homology is contrasted with analogy, which is a functional similarity of structure based not upon common evolutionary origins but upon mere similarity of use Thus the forelimbs of such widely differing mammals as humans, bats, and deer are homologous; the form of

construction and the number of bones in these varying limbs are practically identical, and represent adaptive modifications of the forelimb structure of their common early mammalian ancestors Analogous structures, on the other hand, can be represented by the wings of birds and of insects; the structures are used for flight in both types of organisms, but they have no common ancestral origin at the beginning of their evolutionary development A 19th-century British biologist, Sir Richard Owen, was the first to define both homology and analogy in

the mirror ophrys (Ophrys speculum) The colouring

so closely resembles that of the female wasp Colpa aurea that males of the species are attracted to the flower and pick up pollen during their attempts at copulation

E.S Ross

DOBZHANSKY: Between 1920 and 1935, mathematicians and experimentalists began laying the groundwork for a theory combining Darwinian evolution and Mendelian genetics Starting his career about this time, Dobzhansky was involved in the project almost from its inception His book Genetics and the Origin of Species (1937) was the first substantial synthesis of the subjects and established evolutionary genetics as an independent discipline Until the 1930s, the commonly held view was that natural selection produced something close to the best of all possible worlds and that changes would be rare and slow and not apparent over one life span,

in agreement with the observed constancy of species over historical time

Dobzhansky's most important contribution was to change this view In observing wild

populations of the vinegar fly Drosophila pseudoobscura, he found extensive genetic

variability Furthermore, about 1940 evidence accumulated that in a given local population some genes would regularly change in frequency with the seasons of the year For example, a

certain gene might appear in 40 percent of all individuals in the population in the spring,

increase to 60 percent by late summer at the expense of other genes at the same locus, and return to 40 percent in overwintering flies Compared to a generation time of about one

month, these changes were rapid and effected very large differences in reproductive fitness of the various types under different climatic conditions Other experiments showed that, in fact, flies of mixed genetic makeup (heterozygotes) were superior in survival and fertility to pure types

"Dobzhansky, Theodosius" Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=micro/173/58.html>

INDUSTRIAL MELANISM: Melanism refers to the deposition of melanin in the tissues of living animals The chemistry of the process depends on the metabolism of the amino acid tyrosine, the absence of which results in albinism, or lack of pigmentation Melanism can also occur pathologically, as in a malignant melanoma, a cancerous tumour composed of melanin-

pigmented cells

Melanic pigmentation is advantageous in many ways: (1) It is a barrier against the effects of the ultraviolet rays of sunlight On exposure to sunlight, for example, the human epidermis undergoes gradual tanning as a result of an increase in melanin pigment (2) It is a

mechanism for the absorption of heat from sunlight, a function that is especially important for cold-blooded animals (3) It affords concealment to certain animals that become active in twilight (4) It limits the incidence of beams of light entering the eye and absorbs scattered light within the eyeball, allowing greater visual acuity (5) It provides resistance to abrasion because of the molecular structure of the pigment Many desert-dwelling birds, for example, have black plumage as an adaptation to their abrasive habitat

"Industrial" melanism has occurred in certain moth populations, in which the predominant coloration has changed pale gray to dark-coloured individuals This is a striking example of rapid evolutionary change; it has taken place in less than 100 years It occurs in moth species that depend for their survival by day on blending into specialized backgrounds, such as

lichened tree trunks and boughs Industrial pollution, in the form of soot, kills lichens and blackens the trees and ground, thus destroying the protective backgrounds of light-coloured moths, which are rapidly picked off and eaten by birds Melanic moths, by their camouflage, then become selectively favoured "Industrial" melanic moths have arisen from recurrent

mutations and have spread via natural selection

"melanin" Britannica Online

<http://www.eb.com:180/cgi-bin/g?DocF=micro/385/80.html>