A short, reader-friendly discourse on the accidental rise of creatures great and small—emphasis on accidental.
Which is to say that invertebrate-zoologist Arthur (Zoology/National University of Ireland, Galway) tackles the issue of complexity. How do we account, he asks, for the development over eons of bigger organisms with diverse cells and organs? Before Darwin, the answer was God and nature’s ladder, which had a rung for every living thing from lowest bacteria to highest human beings. Darwin went far to discredit the ladder, but it has taken modern genetics and embryology to come up with a nonreligious explanation for why evolution has produced complexity over time. This happened initially, Arthur notes, by a random mutation that allowed single cells to clump together to become multi-cellular. Then came mutations that changed simple critters’ shapes from round to bilateral, which allowed for left and right halves of the body, a rear and a head end that oriented the creature forward. Over millions of years, some creatures got bigger, and their heads got packed not only with mouths for food, but with eyes and ears and noses, the better to explore the environment, and a brain to control them. Copying mistakes could account for all these changes, Arthur observes, particularly duplications of genes that create redundancies of function. Fish have four gill slits on each side but don’t need that many to breathe. So in some species, the forward pair evolved to become jaws. Besides examples from nature, Arthur points to the commonality in the sets of master genes that program the development of the embryo, from fruit flies to humans. He emphasizes that evolution is messy, neither gradual nor saltatory, in prose that is always gentle and professorial—except when it comes to today’s creationists and Intelligent Design advocates, whom he blasts as blatantly dishonest.
Elegantly and persuasively makes the case that “evolution is part lawn, part bush, part tree, part ladder. It defies simple models.”