Overarching generalised hypothesis: (Click here for alternative, more specific versions)
The Waterside Hypothesis (aka AAH 'weak' form):
The hypothesis that moving through water has acted as an agency of selection in the evolution of humans more than it has in the evolution of our ape cousins. And that, as even relatively weak selection may result in profound and rapid phenotypic changes, many of the major physical differences between humans and the other apes are best explained as adaptations to moving (e.g. wading, swimming and/or diving) better through various aquatic media and from greater feeding on resources that might be procured from such habitats.
(This is an overarching definition which comprises of a series sub-hypotheses, defined below, which provide more detailed, falsifiable predictions. The overall hypothesis is a superset of these sub-hypotheses, therefore it too is testable. It is suggested that if hominids lived in water-side habitats then each sub-hypothesis not only stands on its own but draws synergic strength and parsimony when combined with the others. Click here for discussion and reaction.)
Falsifiable Sub-hypotheses:
The Hominid Bipedalism from Wading Hypothesis:
The hypothesis that wading through shallow water was a major component of the locomotor repertoire of the earliest proto-hominid bipeds.
Falsifiable Predictions:
1. That extant apes should be most predictably bipedal in shallow water than in other substrates.
2. That the paleohabitats of the earliest bipeds should be conducive with significant amounts of wading behaviour.
3. That the differences between the postcranial anatomy of the earliest bipedal hominids and modern humans, as evidenced by the fossil record, should be consistent with specific adaptations for greater wading.
The Nakedness for Drag Reduction Hypothesis:
The hypothesis that selection for greater efficiency, endurance and/or speed through drag reduction whilst swimming resulted in the significant hair loss manifest in the difference between humans and the great apes.
Falsifiable Predictions:
1. Shaving body hair off competitive swimmers should result in gains in swimming performance (efficiency, endurance and/or speed) through drag reduction.
2. There should be a positive correlation between the amount of body hair shaved off and the amount of drag reduction observed in similar-sized competitive swimmers.
3. There should be a 'threshold effect' at the point when hair density increases to the point when the boundary layer surrounding each individual hair fuses into a continuum. (Hence explaining why most semi-aquatic animals - which also tend to move through thick abrasive vegetation - have a thick pelt of hair.)
4. Modern human populations with significant amounts of body hair are not typical of the human universal status and represent a 'reversion' to greater body hair since the last common ancestor of all human beings in certain 'Out of Africa' groups, probably due to an early move into temperate climates.
The Adipocity for Buoyancy Hypothesis:
The hypothesis that selection for greater buoyancy in water, especially in mother-infant pairs, resulted in the increased adipocity observed in humans as compared to most terrestrial mammals, all other primates and great apes.
Falsifiable Predictions:
1. Human infants should be significantly more buoyant than those of the great apes.
2. Human mothers would be able to rescue their infants from a 2m deep pool (requiring an element of swimming) with close to 100% success, whereas chimpanzee mothers would fail to do so almost totally. This differential would be observed even if the permitted time before rescue attempt tended to zero.
3. The accidental drowning statistics should show a positive correlation between the adipocity of people with similar age, sex, race, swimming ability, fitness etc and their likelihood to escape near-drowning incidents.
4. Greater adipocity should be especially correlated with successful endurance swimming in colder sea waters.
The Dip-Sweat Cooling Hypothesis:
The hypothesis that the sweat-cooling thermoregulatory response to overheating seen in humans is a water-side adaptation which evolved as an adjunct to the far more efficient method of cooling of simply going for a dip in near-by bodies of water.
Falsifiable Predictions:
1. Homo sapiens has a greater physiological dependence on fresh water than our ape cousins and is far more wasteful of it, not only in sweat cooling but also in more dilute excretory products.
2. The universal trait of sweat cooling in not supportable for typical human work-loads in equatorial habitats unless replenished by copious amounts of fresh water. Earliest Homo sapiens lacked the technology to transport sufficient water great distances.
3. Going for a dip in a body of water provides a far more efficient (less costly and more rapid) way of reducing body temperature in hot equatorial climates than sweat cooling.
4. The delay before the onset of sweating as the body re-heats after going for a dip, should correspond closely with the average time it takes for a wet body to dry.
The Dental Reduction for Fish-Eating Hypothesis:
The hypothesis that the gradual and progressive dental reduction as seen in fossilised clades associated with human evolution is due largely to a shift in diet towards fish, shellfish and other foods from the aquatic food chain.
Falsifiable Predictions:
1. The size of the dentition seen in mammals specialising in eating fish, shellfish and other foods from the aquatic food chain is less than those typically seen in terrestrial carnivores, folivores and frugivores.
2. There should be a negative correlation in the fossil record between the size of dentition and the likelihood that the associated paleohabitat yielded a significant amount of fish, shellfish or other foods from the aquatic food chain. (Or at least if there is a clear lineage dependancy between a number of fossils, the trend in the change of dentition in that lineage should correspond to greater reliance on aquatic foods.)
3. The earliest evidence of stone tool usage should be associated with paleohabitats where shellfish could have been subjected to easy foraging.
4. Human populations which have greater dependence on the aquatic food chain should have slightly smaller dentition than those who have no dependence on them.
Further sub-hypotheses will be added as time permits.
Algis Kuliukas
2nd January 2005
E-Mail info@RiverApes,com for suggestions and other feedback.
Amendments:
11/11/2004 - On the advice of Marc Verhaegen, I added "..and from greater feeding on resources that might be procured from such habitats."
14/11/2004 - After criticism from Jason Eshleman, I changed "at least in part" to "to a large extent".
31/12/2004 - Further justification of the need for this definition and more detail on sub-hypotheses.
6/1/2005 - Following advice of Craig Hagstrom, the claim was 'beefed up' from 'may be explained' to 'best explained.'