Amen-Moses

Originally posted by Duvenoy:
Getting back to the swimming question: we might be the best primate swimmer (this, to my knowledge, has yet to be shown), but alongside the real aquatic and semi aquatic animals, we are slow and clumsy. We're just not built right for it.

I have no doubt who would win a race inwater between a Hippo and an Olympic swimmer!

Also, the thought occurs: most if not all animals, such as seals and whales, that returned to an a marine life style stayed there, evolving into what we see today.

The AAT does not suggest a marine life style but a flooded arboreal setting (mainly from the geological evidence at the sites of earliest hominid finds). A similar environment is also posited for the evolution of the Hippo and Elephant.

When the climate changed and these areas dried out (probably due to ice ages) the semi-aquatic hominid (along with Elephants an Hippos) was forced back onto land and into competition with other apes more suited to a dry arboreal setting. This resulted in the hominids being forced into using tools and advanced communication to survive.

What most people seem to miss is that although the claim that we are generalists is true it is not the end of the story, why are we generalists? What series of different envoronments did we have to survive through to become generalists in the first place?

Given the large climate changes with resulting sea level changes that the earth has been through in the last 10 MY I can't see why one or more periods of semi-aquatic living is so hard to accept, after all we are definitely not adapted to savannah living (in fact of all the places on earth that we do live savannah is one of the least favourites) nor are we adapted to a purely jungle or forest or tundra or desert etc lifestyle but noone argues against our having lived in those environments at some time.

Personally I see the early hominds as margin creatures, i.e living in the narrow band between heavy forest and open water, maybe on lake fringes and river estuaries, one of the "missing" apes in the modern world is such an ape except of course that is exactly where you find 90% of the human population!

Incidently, there are cats that love the water. Tigers are often found swimming and even lying in the shallows soaking on a hot day.

And there are even semi-aquatic dog breeds, of course we have bred them for that job but given the changes that we have bred in only a few thousand years does anyone doubt that similar changes could occur in the wild given enough environmental stress over say 100KY?

Amen-Moses

Peez

None have been noted. We certainly do not know exactly how our evolution proceeded, and many questions remain, but there are no traits that are inconsistent with the savanah hypothesis (which is more than can be said of the AAT). The point was that a claim had been made (that humans are the only bipedal mammals on a plans environment), and that this claim was false. I would argue that it is irrelevant as well. This is both false and irrelevant. I know that I can easily outrun a porcupine, python, or tortoise. A trained athlete can likely outrun a lot of other animals in the long run. It is irrelevant in any event. I agree that the hippo is semi-aquatic, but the bit about elephants and rhinos is a circular argument. It is certainly known that some relatives of these animals had fur, but there is no indication that either had any semi-aquatic phase. It looks as if Morgan only believes that they have because they lack fur, not the other way around. Why? What advantage might it have had in the water? Forgive me, but LOL! It certainly does not keep water out of my nostrils. Funily enough, no other aquatic mammal evolved this "useful" shape. In fact, they just about all can close their nostrils, unlike us. Or getting water up their nose. Do you want a hypothetical function of the nose? As we evolved to stand errect, and evolved a larger brain, the shape of our skull changed. This tended to leave a smaller nasal cavity. The nasal cavity is crucial for both the sense of smell and as a filter/humidifier for inhaled air. The nose evolved to provide more protected space for this cavity. That was easy, but hard to test as we do not have a lot of independantly-evolved big-brained bipeds to compare us to. On the other hand, we have lots of aquatic and semi-aquatic mammals (and other animals). None seem to have a nose like ours, and in fact most seem to have a very noticable trait (being able to close their nostrils) which we lack. on't over-simplify evolution. Just because something is advantagious for a species does not mean that all species will evolve it. There are trade-offs, and different fitness functions depending on many factors. Do you want some suggestions? Perhaps because they were too small or too large, perhaps because they started with a body that would have to become less adapted before it could evolve bipedalism, perhaps because bipedalism was more of an advantage if you are intelligent, perhaps it depends on diet, hairlessness, etc. Here is a question for you: why doesn't any aquatic or semi-aquatic mammal walk around on its hind legs (are there aquatic kangaroos? )? By the way, there are other bipedal mammals (e.g. kangaroo rat), but not enought to establish any sort of pattern. Again, a simplistic view of evolution. Tallness was not the only factor. Many other animals rear up to see better, the issue is tallness for a given size. Humans are very tall for their size (I cannot think of any animal that exceeds us in this regard). The AAT is naive and silly, so I reject it on the same basis that I reject many other such ideas. Just because one rejects an idea does not make them close-minded. As I have said, it is an interesting thoyght experiment. In fact, an evolution professor of mine had us study it for exactly that reason. "Suggestion"? Anyhow, I was not aware that there was such passion. What is it about evolution that makes scientists think it answers all the questions provoked by the features which so clearly distinguish us from any other mammal?

Peez

Dr Rick

I agree; the book is a captivating and bone-chilling account of what becomes of humans when they are placed in dire circumstances.

Rick

Peez

That is because the only argumtns in favour of the AAT are along the lines of ‘well that's an adaptation for an aquatic environment because such and such an aquatic mammal has it'. The point is that these arguments are naive. No, the only valid comparison is whether the AAT or the savanah hypothesis better explains the observed data. It is quite clear to biologists that the savanah hypothesis is much better. Yup. It is also a great energy storage tissue, which is why it is found in all mammals. What is a more telling trait is the distribution of fat. In aquatic/semi-aquatic mammals like seals, otters, whales, etc., the fat layer is between the skin and anything that needs to stay warm (it is not much good as an ansulator otherwise). In humans, there are many blood vessels that are not covered by much fat, even in obeis people. The head is also poorly protected. Humans are very poorly adapted to living in water, and loose heat extremely quickly when immersed. Not only that, but we are not streamlined, and the addition of fat (in the way that we store it) only makes us less streamlined (have you ever seen a pudgy olympic swimmer?).

Peez

Peez

hy do you think that we have dismissed it just because it allegedly looks crazy? I studied it at university, thought about it, and came to the conclusion that it is naive and silly. And the guy who came up with the Lamarkian evolution theory was at first very much critisized...and it later turned out that there is no inheritance of acquired characteristics. Just because somebody was right about something in the past does not make the AAT any better.

Peez

Baloo

<img src="graemlins/notworthy.gif" border="0" alt="[Not Worthy]" />
This post just, well, sucker-punched my funny bone ... not even the photo shop competition has made me laugh that spontaneously.

pz

I would add that fat is not the insulator in marine mammals. The key structures for conserving heat are the network of vascular countercurrent exchangers that infiltrate the tissue and preserve the temperature of the core blood supply.

We lack such a vascular network. Our fat doesn't protect us from the cold by working as an insulator at all.

Stephen T-B

Just dispose of this: “meerkats? Ostriches? Secretary birds?”
Meerkats scan on their hind legs. They run around on four legs . Ostriches, secretary birds (and you didn’t mention kiwis, emus and cassowaries) only have two legs to start with.

So, moving on - “They all have much richer and more diverse views of the possibilities. “
Now that’s EXACTLY what I’m waiting for.
You’ve tumbled me in terms of my ignorance regarding specialist scientific knowledge, but consider this: I am a moderately well-informed lay person who is under the strong impression that our scientific leaders are stuck like glue on the savannah scenario. If I’m wrong, then I am delighted to hear it, but why hasn’t news of these “richer and more diverse” possibilities seeped out?
Go into the street and ask the first passer-by if he / she knows of these “richer and more diverse” possibilities.
(Knowing my luck you’d bump into some guy who does, but I know if I asked any of my colleagues, they’d not have clue as to what I was talking about.)
So, teach me. Tell me. Put me right. I don’t especially like the AA suggestion - though, like Ergaster I thought it neat. But why am I wrong to think that something distinctive occurred in our ancestry which altered our appearance so dramatically from that of our cousins which also evolved in Africa?
I am in the business of communication. It is important that people like me who work in the media have a proper understanding of what the latest thinking is. I do not want to be in the position of advocating false doctrines because the scientific community didn’t communicate its knowledge in such a way that the lay person can understand it.

(Wyz - you seemed to think the whole of my earlier post was addressed to you. Only the first para was.)

Ergaster

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Uh...birds do, in fact, have 4 limbs....as did their ancestors.

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Funny...you read at least part of my post, but I guess not the rest of it. The one where I said that the professionals DO NOT regard the "savanna hypothesis" as valid and haven't for at least 10 years.

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It is entirely irrelevant whether "the man in the street" knows anything at all about the savannna hypothesis, or AAT, or human evolution in general. What *is* relevant is whether the people who support AAT are up to speed with the relevant discoveries and literature. It is *their* responsibility to keep up with the discipline, if their "theory" is to have any hope of support. If they are flogging an outdated notion of human evolution long after the professionals have discarded it, then one has to wonder about their motives.

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How much time do you have? How much work are you willing to do? How many of your preconceptions are you willing to lose, like: Most professionals would probaly disagree that we differ "radically" from chimps. Just what does "radical" mean, anyway? In terms of comparative anatomy, we are astonishingly similar, far more than we are different.

Or--there is an inference in your post that you think the aquisition of bipedalism was an "event". There is no evidence of this; evolution is a process, not an event.

Or--the assumption in AAT is that bipedalism happened once. Maybe it did, and maybe it didn't. It is true that everyone assumed it was a one-time thing especially a few years ago, but back then we had virtually no fossils at all in the critical time period between 10 and 4 million years ago, so anything we said about human evolution in that time frame was pretty much speculation. In the last 10 years that gap has begun to be filled in, and it is showing us some rather unexpected stuff. And one possible implication of this new stuff is maybe bipedalism did not arise just once in our ancestors. Maybe it only *survived* in our ancestors.

Or--the earliest hominin fossils appear to have been forest-dwellers, or at least inhabitants of woodlands rather moister than "savanna". Bipedalism did not arise on "the savanna". In fact, there is pretty good evidence that the savanna that we see in Africa today did not even exist before about 1.6 million years ago, long after any purported "aquatic phase". There were grasslands, but it is not perfectly clear just what kind they were or how much tree-cover there was.

My point is that there is a limit to the kind of information that can be conveyed on a discussion board. I can tell you that there are several hypotheses about the origin of bipedalism, none of which involve "the savanna" or an aquatic phase. They do, however, try to take into account other information like functional anatomy, the Miocene fossil record, paleoecology and biogeography, and comparative anatomy with the closest fossil relatives of our ancestors (i.e. *not* chimps.). However, if you want details, then you'll have to follow up yourself. References can be provoded.

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You might be a person to ask, then--where do you draw the line between real information and the requirements of space and time? I only ask because I know of several scientists who have been thoroughly frustrated by the vast difference between what they told reporters and what got printed (this tends to be more prevalent in popular press releases). When presented with a fairly complex idea that you have to present in six column inches, how do you decide what stays in and what gets left out?

If you are, say, a science reporter for a newspaper, how much responsibility is on you to do background research?

Just wondering, because I know for a fact that some of the press-release messes I've read in the human evolution field are not the result of scientists failing to provide the correct information....

Oolon Colluphid

Funny you should say that V, but I do...

At least, I've no idea about rhinos (but strongly doubt it: a rhino is a horse in tank's clothing), but 'everyone knows' that elephants are closely related to the Sirenia... and it looks as if elephants did have an aquatic ancestor.

See Gaeth, Short & Renfree, <a href="http://www.pnas.org/cgi/content/full/96/10/5555" target="_blank">'The developing renal, reproductive, and respiratory systems of the African elephant suggest an aquatic ancestry'</a>, PNAS Vol 96, Issue 10, 5555-5558, May 11, 1999.

Not quite sure of it's relevance to the AAH, but I found that a while ago and it's too cool not to mention.

Cheers, Oolon