|
|
Reply to Elaine MorganPhil Nicholls (pn8886@csc.albany.edu)2 Jan 1995 15:41:22 GMT
Elaine@desco.demon.co.uk (Elaine Morgan) writes: > Two fallacies seem to be floating around. First, that > evidence from comparative anatomy is more pseudo than > fossil evidence. The two are equally valid and should > complement one another. The discovery that whales descended > from land mammals was made purely on anatomic evidence, > but nobody dismisses it as a Just So Story. I don't think anyone has claimed that there is anything wrong with the practice of comparative anatomy. For example, I am interested in the evolution of the brain and with the exception of endocranial casts, I work exclusively with comparative neuroanatomy. The issue I believe is what conclusions can and cannot be supported on the basis of comparative anatomy. Taking the example you give the ancestry of the whale was determined on the bases of shared homologies with non-aquatic mammals. In modern evolutionary studies, cladistic analysis has become very a popular method for determining relationships using patterns of shared homologies. Such patterns are the provide a basis for reconstructing phylogenetic relationships. However, you are not trying to reconstruct a phylogeny or establish a phylogenetic relationship. You are reconstructing an ancestor, a protohominid, from characteristics that you consider to be the result of an evolutionary convergence. Your premise -- that hair reduction, sweating, fat distribution and nose shape are aquatic convergences is also your evidence for an aquatic phase in hominid evolution and is a classic example of begging the question. > Second, that fossil evidence refutes AAT. In fact it is > Savannah theory that lacks hard evidence. After the ape/ > hominid split and the fossil gap we get first A. ramidus > from the sediments of a soggy forest. Later Lucy, whose bones > were eroding from sand among crocodile and turtle eggs > and crab claws. Virtually all the Rift Valley hominids died > at the water's edge - lakesides, riversides, flood plains. > Savannah theory readily explains this by saying none of the > non-waterside hominids' bones survived. Richard Klein wrote > in "The Human Career": "The specific site locations reflect > the occurrence of sedimentary traps with good conditions > for bone preservation..(but)..both the australopithecines > and early Homo surely ranged far more widely within tropical > and subtropical Africa, into areas where fossil sites have not > been found or may not exist." That is a plausible suggestion, > impossible to disprove, but it is only a speculation. The hard > fossil evidence is that of bones sinking into mud and silt. The vast majority of ALL fossils come from mud and silt. One of the richest primate fossil sites in Africa is El Fayum, where hundreds of Oligocene anthropoid fossils have been recovered from riverine deposits. Were these aquatic anthropoids? No, they were arboreal. How do we know? Because their anatomy is consistent with that of arboreal primates today. Comparative anatomy, used correctly, can provide meaningful interpretations of the fossil record. No hominid or ape fossils show any evidence of aquatic adaptations. None of the living primates that are comfortable in the water show any evidence of the aquatic convergence. Now we have fossil hominids -- mostly skulls but occasionally some postcranial materials as well. Most are found near sources of water. A ramidus may or may not prove to be a hominid but A. afarensis definitely was. Was it aquatic? Well, it may in fact have waded out into shallow water to forage. However, comparative anatomy tells us only that it was a terrestrial biped. Some have suggested, based on the curvature of the toes and fingers, that A. afarensis continued to climb into trees. Where would a terrestrial biped most likely have lived in Africa at this time? In the forest? Forests were shrinking right about this time. The savannas were expanding. All known hominids ( A. ramidus excepted for the moment) are found in mud and silt deposits that border what at the time were savannas. Now if A. ramidus proves to be a real hominid then we have some evidence that bipedalism was perfected in the forest. Some anthropologists have held this position for some time, noting that primates that are suspensory feeders like gibbons are exclusively bipedal when they are on the ground. However, we know that hominids eventually moved onto the savanna and this makes it reasonable to conclude that many aspects of hominid morphology are a result of adaptation to the savanna. > Laetoli is an exception. Sediments there are airborne, not > waterborne. But the area of the famous hominid footprints also > bore footprints made at the same time by an untypically varied > assemblage of other creatures, suggesting that some at least > (possibly including the bipeds) were transients fleeing the > fallout from the successive eruptions of the volcano Sadiman > which preserved the prints. What the Laetoli footprints tell us is that a terrestrial biped made its way over the ash deposits. Possibly A. afarensis, possibly some different species of hominid (the lack of curvature in the toes of the feet may indicate it was not A. afarensis). > The South African sites are different and more recent, > from a time when savanna conditions had become established. > If ramidus and afarensis had been discovered before the > Taung baby instead of decades later, it is certain that the > savannah explanation of ape/human divergence would never > have got off the ground. Only academic inertia keeps it extant. > It is time they switched off the life support system. Recent dating techniques are pushing the times back toward three million years, so they are not significantly more recent than, say, AL-444 (Johanson's male A. afarensis). The South African sites are limestone caves and the hominid fossils found their are most likely deposited by predators. Had the Hadar materials been discovered before Taung we might have seen less resistance to the acceptance of Australopithecines as hominids but I doubt if it would have changed our conclusions about early hominid paleoecology. Australopithecines were terrestrial bipeds and the savannah is the most likely place for them to have been terrestrial bipeds. Your aquatic detour is an extraordinary claim which requires extraordinary evidence. Having read _Aquatic Ape_ and _Scars of Evolution_ I find no such evidence presented by you. I would be happy to present my reasons, point by point, if you would like. Academic inertia is a fact. People who have held certain ideas to be true are unwilling to accept that they may be wrong. However, I don't think you can blame academic inertia for the failure of the AAH to make headway in mainstream anthropology. Whether our ideas about the role of the savannah are true or not has no bearing on the validity of the AAH. The Sherlock Holmes maxim you quote in your book does not apply to science. A theory or hypothesis is supported by evidence and not by a lack of evidence for competing hypotheses or theories.
--
|