What’s our line?
- The Neandertals: Changing the Image of Mankind by Eric Trinkaus and Pat Shipman
Cape, 454 pp, £20.00, April 1993, ISBN 0 224 03648 3
- In Search of the Neanderthals: Solving the Puzzle of Human Origins by Christopher Stringer and Clive Gamble
Thames and Hudson, 247 pp, £18.95, May 1993, ISBN 0 500 05070 8
- Self-Made Man and His Undoing by Jonathan Kingdon
Simon and Schuster, 369 pp, £20.00, March 1993, ISBN 0 671 71140 7
Up until the mid-19th century, humanity and the animal world were separated by an unbridgeable morphological void – there was no coherent body of evidence to suggest anything other than the standard Biblical story of human origins. Everything changed, however, in 1856, when the first Neanderthal fossils to be recognised as such were unearthed – just three years before the publication of The Origin of Species.
Vol. 16 No. 3 · 10 February 1994
I was disappointed, although not surprised, by Henry Gee’s curt dismissal of the ‘aquatic ape’ theory (LRB, 27 January). Since Alister Hardy first proposed that humanity’s ancestors inhabited the shoreline rather than the savannah, opposition to the theory has been long on derision and short on argument. Gee referred to our ancestors’ loss of fur and development of sub-cutaneous fat; he could also have mentioned their development of an unusual and water-prodigal sweating mechanism, breathing through the mouth and walking exclusively on two feet. These departures from the primate norm would make good selective sense for a shore-dwelling species; in a savannah environment most of them would be positively counter-adaptive (‘We have to admit to being baffled about the origin of upright walking’ – Sherwood Washburn). I would be interested to know what account of these developments Gee prefers. Then there is the matter of the theory’s own growth and dissemination. Gee refers to its popularity with feminists (a reference to the excellent work of Elaine Morgan?); this he ascribes to its making women look more highly evolved than men – fatter and less hairy, you see. It might be nice to see some references supporting this assertion, too.
Vol. 16 No. 4 · 24 February 1994
Henry Gee (LRB, 27 January) is strangely misinformed about the aquatic theory of human evolution. He has clearly read nothing that has been written about it in the last 22 years. AAT (aquatic ape theory) addresses the question of why humans are so different from apes in so many respects – bipedality, hairlessness, descended larynx, eccrine thermoregulation, tears of emotion, subcutaneous fat, sebaceous glands, ventro-ventral copulation, and half a dozen other features. The orthodox scenario assures us that humans evolved these differences by adapting to a savannah environment, but fails to explain why not one of these features is found in any other savannah primate (or in some cases in any other land mammal). The predictive value of the savannah theory has proved to be nil. The latest blow to its credibility has been the growing consensus that the savannah ecosystem as we know it did not emerge until two and a half million years ago, whereas there were bipedal hominids four million years ago. Bipedality, hairlessness and speech are among the major hallmarks of humanity. In terms of the bankrupt savannah hypothesis, scientists cannot agree on an explanation of any of them.
Henry Gee writes: My dismissive treatment of the aquatic ape theory has clearly caused some offence. As I understand it, proponents of AAT note several anatomical, physiological and behavioural features of modern humans that set them apart from the Great Apes. These include relatively large amounts of body fat, paucity of body hair, face-to-face copulation, a propensity to sweat profusely through the skin, and so on. Furthermore, these features are held to be inconsistent in a creature conventionally thought of as having evolved on the hot, dry savannahs of Africa. Conversely, many of them are seen in aquatic mammals such as whales and seals. Therefore it is simpler to suppose that humanity underwent an aquatic stage in its history.
This scheme fails for several reasons. First, the AAT marshals its evidence by recourse to syllogism: aquatic animals are fatty, humans are fatty, therefore humans are by nature aquatic. Such a link is, at best, suggestive and correlative – a hypothesis rather than a theory.
Second, the proponents of the AAT attempt to bolster it by knocking a straw man – the idea that humanity evolved on the savannah, and that if this idea is correct there should be evidence for it in modern physiological and behavioural adaptations. There are two things wrong with this assumption. One is that just because most human fossils in Africa tend to be found in regions that are hot and dry, this doesn’t mean that those are the places that humanity evolved: they’re simply the places that people have looked. As Jonathan Kingdon notes in Self-Made Man, the most human-like of the Great Apes is the bonobo or pygmy chimpanzee (Pan paniscus), a creature with a social behaviour uncannily similar to that of some human societies – including face-to-face copulation. The bonobo is a forest creature which (as far as we know) never ventured onto the savannah or into the water. It is possible that fossil hominids lie undiscovered in tropical forests, or along ancient shorelines long since inundated by the post-glacial rise in sea-level. It is also entirely possible that such fossils will show evidence of aquatic habit, although it’s unlikely. Until these fossils are found, we won’t know either way. This is why most serious students of paleoanthropology would prefer not to speculate on the irrecoverable habits of our ancestors: their speculations would be based on the still pitifully small body of evidence available, most of it gathered from areas now under savannah – because that’s where they’re easiest to find.
The further misapplied assumption in the straw-man case concerns the nature of adaptation. A strict (and over-simple) interpretation of Darwin suggests that an animal and all of its parts is perfectly attuned to the environment: imperfection in adaptation is soon weeded out by natural selection. However, even Darwin realised that natural selection can work only within the strict limits imposed by the genetic variation it is offered. As Stephen Jay Gould has shown on several occasions, this variation is constrained, in turn, by evolutionary history. Many features (most famously the appendix) have little or no adaptive value – they are there only as a vestige of long-forgotten ancestry. If adaptation ruled, strict natural selection would have evolved the appendix away long ago, we’d all be perfect machines, and appendectomies wouldn’t have been invented. This raises a problem for proponents of the AAT. On the one hand, they stress the imperfection of human adaptation to the savannah, noting how much better our ancestors would have been in the water. At the same time, it is the vestiges of such features in plainly non-swimming modern humanity that they use to promote their idea. Were adaptation as strong as they assert, both savannah and aquatic-led adaptations should have been expunged long since, and there would be no AAT worth shaking a stick at.
Third, subscribers to the AAT base their ideas on an analysis of what anatomists call ‘soft-part’ characters – features of physiology (sweating), behaviour (copulation) and external appearance (distribution of subcutaneous fat and body hair). Such features are notoriously plastic and prone to variation for all manner of reasons, not necessarily adaptive. Proponents of the AAT have been rather selective with their evidence. First, some of the soft-part features they cite are highly variable even within modern humanity, thus making their status as ancestral legacies somewhat dubious. For example, my own luxuriant whiskers would be an impossibility were I Japanese rather than Jewish. Likewise, my generous waistline and Pooh-like inclination to stoutness would look daft on the etiolated figure of a Masai or Ethiopian marathon-runner. The trend to suppress the appreciation of natural human variation has allowed ideas such as the AAT to spread.
Perhaps more important, the AAT says nothing about bones and teeth, the parts of the body most likely to be preserved as fossils. The problem here is that aquatic specialisations are very hard to detect in such remains. That whales and seals are aquatic can be discerned easily from their skeletons and dentition. But what do we do about – say – otters? Sea-otters spend a large part of their lives at sea, but this is difficult (if not impossible) to see from their skeletons. By the same token, sea-otters are every bit as furry as their landlubber cousins. And would you ever know, from its bones, that your golden retriever dives into the nearest puddle at every opportunity? Real scientists are constrained by the real evidence that they have to hand, in the form of real bones, and real teeth, once the property of real hominids. None of these show any evidence for an aquatic phase of our ancestry, which, at present, is no more (or less) likely than (say) the existence of extraterrestrial intelligence.
Mr Edwards (Letters, 10 February) challenges me to support my assertion of the popularity of the AAT with feminists. Ms Morgan notes that I have ‘clearly read nothing that has been written about [the AAT] in the last 22 years’. The latter, at least, is true. About ten years ago, a friend gave me a book on the subject. It was written by Ms Morgan, but I didn’t get any further than the title: The Descent of Woman.