No bones about it

Abstract

A remarkable new book of photographs of vertebrate skeletons celebrates how evolution can adapt basic structures to extraordinarily diverse functions, writes Nigel Williams. A remarkable new book of photographs of vertebrate skeletons celebrates how evolution can adapt basic structures to extraordinarily diverse functions, writes Nigel Williams. Molecular genetics has shifted the focus in the biology of animal structures towards the genes by which they are built, with some spectacular insights. But a remarkable new book goes back to the hardware with an impressive collection of black and white photographs of almost 200 vertebrate skeletons of currently existing animals, showing both the remarkable similarity and diversity in vertebrate evolution. The author, Jean-Baptiste de Panafieu of the National Museum of Natural History in Paris, has collaborated with the photographer Patrick Gries and colleagues at several major French zoology collections to produce a stunning, dynamic snapshot of current vertebrate diversity as a result of the power of natural selection and evolution. “All creatures alive today are descended from a population of single-celled organisms that lived some billions of years ago. Since the first animals appeared, millions of species have been born (the majority of which are now extinct), including our own, Homo sapiens”, he writes. “Even when life science makes no explicit reference to these principles, all of them work within the framework of evolution,” he says. He points out the problems facing evolutionists in explaining past events no longer in view. “The theory of evolution is the sole explanation that unifies a vast accumulation of data from various scientific disciplines. Like history, it describes events in the past and is therefore not susceptible to observation, but it draws support from a multitude of proofs that are independent of one another, such as from genes and fossils.” The pictures beautifully illustrate how the elephant's enormous skull, which can comprise up to one third of the weight of the entire skeleton, has led to the shortening and thickening of the neck vertebrae to help carry the weight. Contrast that with the giraffe neck vertebrae which have each elongated to give the animal the height it now displays. Similar elongation has occurred in the graceful neck of ibises, also shown in the book. But in animals such as the snakes, duplication of the vertebrae has been key to length in their skeletons. And de Panafieu is keen to tie these remarkable structures in with modern biology. “The theory of evolution has been enriched by many studies… These days, molecular biology plays a very important role,” he writes. From the diversity of skeletons on show in the book, he highlights those of the salamander and the antelope. The former has a naked, glandular skin, the other a shaggy coat; one is flat against the ground while the other stands upright. But they both have a head and four feet. “This observation may seem banal, but such a combination is rather rare in the animal world. Actually from the jellyfish to the sea urchin, a great number of animals have no head at all. As to feet, insects, which make up the great majority of species on the planet, have six of them. Crustaceans have ten or more and centipedes up to seven hundred and fifty. Snails and worms have none at all.” He covers some of the history of comparative anatomy and evolutionary controversy. “For Geoffroy Saint-Hilaire, homology was the sign of a family relationship, thus the result of evolution. This view was not shared by all naturalists. For instance, the English anatomist Richard Owen also used the concept, but only as a means of classifying animals more precisely, since he rejected the idea of evolution.” Only after the publication of The Origin of Species, “homology became an important element in helping to identify phylogenetic relationships among species,” he writes. But de Panafieu's dramatic display of vertebrate form, from flying fox to crocodile and piranha to platypus, also comes with a message of concern: “Today, some five thousand species of vertebrate are more or less threatened with extinction; a third of the amphibians, half the turtles, one mammal in four, and one bird in eight,” he writes. As to the other species, “the rate of extinction is reaching a level comparable to the great episodes of mass extinction in prehistory. Hunting and fishing are sometimes to blame, but the major threats come from the destruction of natural environments, from the introduction of alien species, and from the many forms of pollution. To these factors are now added the present warming of the climate”. The stark lesson is to appreciate the adaptations of these living species before they join the list of fossils.