Cynic1 writes:
You forgot the breathing aspect of the theory, in that we are the only land mammal with breath control and a descended larynx, which are telling indications of a possible aquatic ancestor.
Also, the only other animal with a perpendicular gait is aquatic (the penguin).
We waste a great deal of salt to sweat, which would seem detrimental in the savannah.
No other land animal cries, but the walrus, otter, and various marine birds and reptiles do.
Our glands which secrete oil are huge compared to chimps, and these oil glands are often used for waterproofing.
The kinds of control which arise from a descended larynx have nothing to do with breathing in water; it is fairly plainly linked to vocalization. Furthermore, the larynx is not descended at birth; but comes later in childhood; but the breath control which Morgan also like to invoke is present from birth. The human larynx is nothing much like the larynx of truly aquatic animals. Fossil evidence also indicate that this arose much after the development of bipedalism.
The comparison with a penguins proposed as a line of evidence is hilarious. Have you seen a penguin walk?
The invocation of sweat is interesting; why would an aquatic animal need to sweat? The answer proposed by Morgan is that they need to get rid of salt (assuming salt water lifestyles). This is contradicted by the evidence, which shows that human sweat does not in fact have any excessive concentration of salt as is found in animals where salt secretion is an adaption.
The claim about animals crying is wrong. Most vertebrates shed tears. Morgan originally tried to distinguish "emotional" tears; but the association of this subtle distinction with acquatic adaptions is odd and ridiculous; and even the sources she was using proposed examples of other animals shedding emotional tears.
Morgan has indeed publically retracted some of her arguments about sweating and tears in response to various counter examples. See this
Usenet post from May 1996. This is not, alas, prevent the recurrence of this rather dreadful argument.
I have not heard the one about oil before; but I'll bet that there is no credible basis or argument for thinking that humans ever had glands for water proofing or any need for such a thing. I'll look into it if you can give a reference.
Cheers -- Sylas