Marvels of Evolution

I'm reading a recently published work by famed evolutionary biologist Richard Dawkins, THE GENETIC BOOK OF THE DEAD. The title refers to this book's dominant metaphor of a palimpsest, a document whose text has been written over, sometimes more than once. On a literal palimpsest, the original words have been obliterated by the later ones. That isn't the case with the genetic, anatomical, physiological, and behavioral traces that reveal the ancestral past of animals and other living creatures, so the metaphor isn't perfect (as Dawkins notes) but still makes a fruitful device for contemplating the evolution of life on Earth. As the cover blurb puts it, every creature can be regarded as "an archive of the worlds of its ancestors." What do an animal's body structure, genome, and behavior inform us about the environment that shaped it?

Naturally, it's easy to tell a herbivore's skull from a carnivore's by their teeth. We can learn much more about the past of various species by observing present-day creatures, though. A lizard with skin like rocks and sand must have descended from ancestors that lived in a desert; the forebears of insects that look like twigs must have evolved in trees. Many other types of visual deception exist, some truly weird. The "palimpsest" can tell us about animals whose predecessors left the ocean to become land-dwellers, returned to the sea, and some cases even developed back into terrestrial animals. Convergent evolution can result in animals that look uncannily similar although not at all closely related, because they've developed to fill the same kinds of environmental niches. One page illustrates a variety of marsupials alongside their placental mammal counterparts, some almost indistinguishable to a casual glance. "Divergent" evolution, on the other hand, concerns closely related species that have developed so differently in different habitats that they look nothing alike, e.g., whales and hippos. And those topics take us less than halfway through the book. In an exciting twist in the final chapter, for instance, we learn that we may have acquired a nontrivial portion of our genes from ancient viruses.

For another mind-blowing work by Dawkins, check out THE ANCESTOR'S TALE. This one adopts its metaphor from Chaucer's THE CANTERBURY TALES, which portrays a group of pilgrims coming from far and wide to unite and travel together. Beginning with modern humans, Dawkins follows the evolution of life backward by successive stages to each most recent common ancestor -- our common ancestor with other hominids, then the shared progenitor of hominids and other apes, through primates, placental mammals, etc., back to the hypothetical original ancestor of all life on our planet. Of course, as the author points out, no matter what modern-day creature we start from, we ultimately end up at the same point. He starts with Homo Sapiens simply because that's us. THE ANCESTOR'S TALE is the most comprehensive survey of the development of life on Earth I've ever read.

Some animals and plants are so odd -- to human observers -- that an SF author wouldn't need to search far to discover concepts for bizarre aliens right here on our world. Reverting to THE GENETIC BOOK OF THE DEAD, I find the chapter on convergent evolution particularly interesting. It's often claimed that if life exists on other planets, the inhabitants won't look anything like earthlings. But why not? If we discover a planet with geography, climate, gravity, and atmosphere similar to Earth's, couldn't those environmental conditions lead to the development of organisms that strongly resemble the plants and animals we know? Biological constraints work the same everywhere on Earth, so why not on other Earth-like planets? There could even be humanoid or quasi-humanoid intelligent beings on such a world.

Margaret L. Carter

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