Genetics and natural selection typically take front stage in discussionsof evolution.Such has been the case for a long time, and may be for sometime to come.BUT in "Shapes of Time," McNamara makes a strongcase for including growth development in the mix in deciding how, why, andwhen organisms came to be the way they are (or were).
McNamara's mainthesis is that three major developmental trends -- 1) Peramorphosis; 2)Paedomorphosis; and 3) Hypermorphosis (a twist on Peramorphosis) -- producea good deal of the observable variability out there.He proceeds to makethe case that changes in rates of development and growth (i.e.,heterochrony) can have a major impact as an evolutionary process, and thatheterochrony deserves a more prominent place in evolutionary theory.
Justso you know what he's talking about...1) peramorphosis is a condition wheregrowth or development proceeds beyond that observed in the ancestralcondition; 2) paedomorphosis is a condition where development does notreach the state observed in the ancestral condition; and 3) hypermorphosis(a form of peramorphosis) is a condition where not only does growth anddevelopment surpass the ancestral condition, but growth and developmentproceeds longer than in the ancestral condition.
McNamara does anexcellent job of tying together his thesis in the last chapter by applyingvirtually everything he talked about throughout the book.In that chapterhe addresses human evolution, and does a great job of showing how, in termsof heterochrony, we are a "cocktail organism," showing signs ofpaedomorphosis here, perimorphosis there, and hypermorphosis in anothersituation.
Readers entrenched in the traditional view of the "newsynthesis," i.e., genetics + natural selection = evolution, will findthemselves shaking their heads here and there as they read this book (Ieven did that a couple of times and I'm a relatively strong proponent ofdevelopment being a significant factor in evolution).If you press on youwill find that McNamara makes a sensible, supported case for the importanceof heterochrony as being an important factor in evolutionary theory.
Thequestion I have is this: "What is the source of heterochrony indevelopment?"McNamara doesn't address this directly, but hisdownplaying the role of genetics suggests that genetic variability codesprimarily for what happens, not when or how fast it happens.This is aquandry!What controls and passes on information about the timing ofdevelopment and growth if not genetics?In any case heterochrony exists ingrowth and development.That is not debatable.
I support McNamara'sposition that growth and development play a major role in evolution.Iwonder what it will take to get those factors included in mainstreamdiscussions on evolutionary theory?
Good job to Kenneth McNamara!Heprovides good food for thought in this offering.
5 stars.
Alan Holyoak,Dept of Biology, Manchester College, IN
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