Review: Evolution, a suitable case for treatment
- 19 January 1991
- From New Scientist Print Edition. Subscribe and get 4 free issues.
- ADRIENNE ZIHLMAN
The Scars of Evolution: What Our Bodies Tell Us About Human Origins by Elaine Morgan, Souvenir Press, pp 196 12.95 Pounds.
How did the human species come to be? Under what conditions and for what purposes did humans evolve? Questions like these keep the topic of human evolution at the forefront of human interest. Elaine Morgan, well known as a screenwriter and author of books and articles on the aquatic ape theory, focuses here on the specific issues of what do our bodies suggest about our evolutionary past? At least one chapter is devoted to each 'scar:' bipedalism, naked skin, sweating, salty tears, fat, breathing and sex. All are entertainingly discussed with the hidden purpose of supporting the thesis that the human lineage went through a phase of living in the water like dolphins or seals before climbing ashore to become the fossil hominids that we know.
She sets up a false dichotomy between 'the aquatic theory' and 'the savannah theory,' Morgan's code name for other prevailing reconstructions of human evolution. The fact that scientists disagree about aspects of human evolution seems to invite volumes of uninformed or partly informed speculation on this fascinating subject. Morgan argues that since the experts say silly things, make mistakes and do not have all the answers, it follows that her aquatic theory is as good as, or better than the savannah theory. She compares herself with Charles Darwin, Albert Einstein and Alfred Wegener, the original proponent of continental drift, as another creator of a radical idea, ridiculed by the scientific establishment, that will eventually prove to be right.
This is fair enough. Science can be conservative and resistant to change, even though the main function of science is finding better explanations for the phenomena of the natural world. Darwin provided a rational explanation for the fossil record, for comparative anatomy and for biogeography. Einstein accounted for electromagnetic, atomic and gravitational effects that hitherto had not been understood. Wegener's ideas explained the shapes of continents and geological continuities at their margins. These three sets of theories continue to be endlessly productive in illuminating the observable manifestations of life, Earth and the Universe.
What, then, is the explanatory power of Morgan's aquatic ape theory? She claims that it accounts for the ditribution of human fat, sweating, descended larynx, suppression of oestrus and small olfactory lobes. According to Morgan, these 'scars' are anatomical-physiological responses to the 'unique predicament' of an acquatic habitat. She makes her case eloquently in the manner of a good barrister, emphasising the items that support her brief and ignoring the mass of evidence against.
One reason why anthropologists have largely ignored her previous book is that the issues she addresses are not the central questions of the discipline. Our present understanding of early human evolution is based on comparative anatomy, which shows us to be most like the living African apes. The fossil record has yielded hominids from geological deposits in eastern and southern Africa dated to more than three million years ago. These fossils resemble chimpanzees in their small brains, dental development and curved hand and foot bones; they are unique in the large size of their molar teeth, in body proportions and in pelvic anatomy.
Molecular genetic studies suggest a divergence of the human and chimpanzee lineage between 5 and 7 million years ago. Some of the debated questions are: What did the common ancester of apes and humans look like? What was the diet of early hominids? How did they divide their time between the ground and the trees? How many species of early hominids were there?
Not only does Morgan not address any of these issues, she ignores the fossil record altogether. But surely this is where one must look for the 'evidence' of her aquatic theory. Hominids that lived more than 3 million years ago, who were then only recently descended from an aquatic forebear, should present far more anatomic evidence of that heritage than modern humans do. Morgan the advocate is wise to skirt this issue, because the australopithecines show none of the streamlining and reduction of limbs that is characteristic of many different species of acquatic mammals. Rather, the oldest hominids, Lucy and her kin from the Afar in Ethiopia, have curved hand and foot bones that bespeak a recent descent from the trees rather than an ascent for the depths.
Morgan does not concern herself with the 'hard evidence' of bones and teeth, the ony data we have for what these early ancestors were like, how they moved, what they ate. Instead she weaves stories about soft anatomy like fat, skin and tear ducts, that leave no clues whatever in the fossils and so are impossible to validate. Most of the anatomical differences between ourselves and and chipanzees, with the exception of bipedalism, have clearly evolved within the past 3 million years, and so they are best explained as different adaptations of a forest-dwelling and a ground-living hominid rather than by appeal to a hypothetical ancestral swimmer, for which there is no fossil evidence.
What, then, does the aquatic theory explain that is relevant to human evolution? It gives no sense of what individuals did, how they grew up, fed, found mates and reared offspring. It sheds no light on the accumulating data from comparative anatomy, the fossil record, and molecular evolutionary studies. As a teacher, I have observed that the attraction of acquatic theory to some students in my introductory anthropology course is that it 'explains everything,' and therefore would make it unnecessary to learn all that tedious stuff about fossils, anatomy, ecology and DNA - if only I weren't so unreasonable as to insist on their learning it.
The hypothesis of an acquatic phase in human evolution is an entertaining fantasy, with intimations of the origins of life in the Precambrian sea and our prenatal float in the amniotic sac. Morgan tells her story well, and the reader will learn some interesting facts about human anatomy and physiology, but the actual evidence that we have in hand for hominid evolution is mostly missing from her scenario.
Adrienne Zihlman is Professor of Anthropology at the University of California, Santa Cruz.