physiology and morphology, evolutionary systematic biology,evolutionary genetics, molecular evolution, and human evo-lution.. First, the field of molecular evolution, from being scarcely
Trang 1physiology and morphology, evolutionary systematic biology,
evolutionary genetics, molecular evolution, and human
evo-lution Research in all of these fields, and the interdisciplinary
overlaps between them, have accelerated in the past 30 years
Two areas of explosive research deserve special mention
First, the field of molecular evolution, from being scarcely
existent in 1950, has become a burgeoning field comprising a
large part of the research program of evolutionary biology
(Higgs and Attwood, 2005; Edwards, 2009) It was realized
early on that, once available, molecular sequence data, of
ei-ther amino acids or DNA, would be ‘‘documents of
evo-lutionary history’’ (Zuckerkandl and Pauling, 1965) and that
branching sequences, ancestral states, and rates of evolution
could be estimated from such data This realization has proven
abundantly true, and molecular data now form the basis of the
phylogenetic estimates for large swaths of the tree of life
(Felsenstein, 2004;Hall, 2011;Hillis, 2010)
Molecular data have contributed to the understanding of
not only evolutionary history but also evolutionary
mech-anisms In the 1960s, protein electrophoresis revealed high
levels of genetic variation in natural populations, which
an-swered old questions about the amounts of natural genetic
variation and posed new ones about the maintenance of
variation (Lewontin, 1974) The advent of DNA sequencing
has revolutionized evolutionary molecular genetics (Kreitman,
1983), and such data now allow hypotheses about the relative
importance of drift and selection on particular loci and
regions to be effectively tested (Charlesworth and
Charles-worth, 2010) As well, the sequencing of whole genomes of
an ever-expanding variety of organisms has led to the
emer-gence of comparative genomics, in which entire genomic
structures can be compared, and their evolutionary histories
and the forces shaping them studied (Lynch, 2007;Edwards,
2009)
The second is the field of evolutionary developmental
biology, or ‘‘evo devo’’ as it is known, another field that scarcely
existed in 1950 It too has become a vibrant research program,
focused on the study of the developmental pathways by which
organismal features are produced, the genetic basis of
alter-ations in these pathways that are evolutionarily incorporated
within lineages, and the biases or constraints that may be
im-posed on phenotypic evolution by these alterations Most of
evolution is the modification of preexisting structures, and
these structures arise in the organism via a process of epigenetic
(in the original sense:Haig, 2004) development Thus, most of
evolution is the modification of preexisting developmental
programs To understand phenotypic evolution, one must
understand the variations that alterations of the developmental
program can give rise to, their natures, and frequency, and these
studies are the domain of evo devo (Carroll, 2005;Carroll et al.,
2005;True, 2009;Wray, 2010;Stern, 2011)
One of the most exciting developments in this field has
been the discovery of a number of developmental regulatory
genes, such as Hox genes, that regulate the spatial expression
of genes in developing animal embryos, and which are
con-served among taxa as disparate as arthropods and vertebrates
The two major groups of bilaterian animals – the protosomes
(Ecdysozoa and Lophotrochozoa) and the deuterostomes
(Chordata and Echinodermata) – share a common genetic
regulatory repertoire and are characterized by an extensive
cluster of Hox genes that bind to DNA and control interacting networks of developmental regulators and key structural genes (Knoll and Carroll, 1999) (Figure 2) This repertoire of genes, which was present in the common ancestor of the Bilateria, has been referred to as a ‘‘genetic toolkit’’ for the development and evolution of basic animal morphologies, and under-standing their action and evolution will aid in underunder-standing such features as germ layers, coelom formation, and spatial organization (Carroll et al., 2005)
Darwin’s Five Theories Although Darwin often used expressions such as ‘‘my theory,’’
he actually proposed a number of distinct, though related, theories Some, such as his theory of inheritance, termed
‘‘pangenesis,’’ were wrong and are of historical interest only But a cluster of other theories has been borne out by sub-sequent developments in evolutionary biology, and it is useful
to consider these ideas here.Mayr (1991,2001)has identified
a set of these ideas as ‘‘Darwin’s five theories,’’ and his usage has been followed and adapted by later authors (Futuyma,
1998, 2009; Coyne, 2009), and the following account is adapted from this approach
The first is evolution as such, the simple idea that later organisms are the modified descendants of earlier organisms This idea had also been advocated by Lamarck Darwin con-vinced essentially all of his scientific contemporaries of the truth of this proposition The evidence for this may be found
in any evolution textbook (e.g., Freeman and Herron, 2007; Hall and Hallgrimsson, 2008;Futuyma, 2009), and in more popular expositions byCoyne (2009)andDawkins (2009) The second is common ancestry, which had been rejected
by nontransformists such as Cuvier, who held that the four ‘‘embranchements’’ of animal life (Vertebrata, Radiata, Articulata, and Mollusc) were so essentially different that they could not be connected by any possible transformation (Young, 2007) Common ancestry may seem to follow from evolution
as such, but it does not: Lamarck, it will be recalled, proposed continual spontaneous generation, with each origination pro-gressing up the chain of being, and thus not being genea-logically related to earlier or later originations.Darwin (1859,
p 490)proposed that life had been ‘‘breathed into a few forms
or into one,’’ and thus most or all organic beings would be connected by a single tree of life This contention has been abundantly borne out by phylogenetic studies within eu-karyotes, but the eukaryotes appear to be chimeric in their origin, incorporating by lateral or horizontal gene transfer both Archaebacterial and/or Eubacterial genes in their nuclear and organellar genomes A phylogenetic tree based on small sub-unit RNA places the eukaryotes as sister to the Archaebacteria (Knoll, 2003), but large-scale genomic analyses are in dis-agreement about the nature, extent, and phylogenetic signifi-cance of the shared genomic components Although some whole genome incorporation via endosymbiosis (e.g., mito-chondria) is well established, the possibility of extensive lateral transfer of genes among prokaryotes and early eukaryotes has ledLynch (2007)to ask if life is a tree, ring, or web; resolution
of the relationship among the domains of life remains a major task for phylogenetics (Gribaldo et al., 2010) (Figure 3)
Evolution, Theory of 395