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Characters provide basis for classifying
• Characters are traditionally phenotypic features
(morphology, life cycle, etc.)
• But now you can also measure genetic sequences
directly
• Homologous characters: similarities attributed to
shared ancestry (e.g., mammal forelimbs)
• Analogous characters: similarities due to
convergent evolution (e.g. wings of birds and
insects)
Homology
Analogy
Analogy vs homology pitfall
Is a 4-chambered heart an homologous or
analogous character between mammals & birds?
Homologous
Analogous
“Agency” of selection
• At what level does natural selection occur?
• Darwin “organismal”
• But selection can act at other levels
– Genes
– Cells
– (Organisms)
– Groups (social insects)
– Species?
Group vs. Individual Selection
Controversy
Selection at any higher level than that
of an individual is essentially "impotent“
and is "not an appreciable factor in
evolution" (1966:8; cf., Williams 1992).
“Many, perhaps most, evolutionary
biologists believe that it [group selection] is
only rarely an important force of evolution.”
(Futuyma 1998, p. 352)
It is sometimes said, “Group selection was
vanquished in the 1960s by William Hamilton and
his ‘gene’s eye view’ of selection, which is the basis
of Richard Dawkins’ notion of the selfish gene.”
“The fundamental unit of selection, and
therefore of self-interest, is not the species,
nor the group, nor even, strictly, the
individual. It is the gene, the unit of heredity.”
(Dawkins, 1976)
“Efficacy” of selection
• Does natural selection account for all of
evolution?
• “Constraints” may channel evolution
– Developmental
– Structural
“Scope” of selection
• Can gradual microevolution account for all
of evolution?
• What about mass extinctions?
• Species selection?
Your vessel (or host person) is a
transient tool designed to
• transmit genes
• not necessarily live long & prosper & be
happy…
An itinerant selfish gene
Said ‘Bodies aplenty I’ve seen.
You think you’re so clever
But I’ll live for ever.
You’re just a survival machine.
Richard Dawkins