| From: Kirsten | 19/11/99
13:18:46 |
| Subject: Ape/Human Evolution | post id:
8723 |
Oh no, another evolution thread! (I promise it's different). As a first year uni student you are taught that humans and (the other) great apes diverged some 5 million years ago (or so) and that in the mean time there have been all kinds of intermediate Australopithecines and Homo species leading up to Homo Sapiens. At the same time no-one has ever found anything ancestral to chimps or gorillas for the same time period. At the time it occured to me that maybe the split was considerably more recent and that the three Austalopithecines were actually the ancestors of humans and chimps and gorillas (A. robustus - gorilla, A. boisei - chimp, or something along those lines), but of course as a numpty undergraduate the idea is soon dismissed as the lecturer tells you what is really the case. Some time later I encountered a (respectable and much published) geneticist who was proposing a similar idea (apparently it would fit quite nicely with the molecular clock), but he was loudly and quickly argued down by the physical anthropologists. What I would like to know is, does this idea appeal to anyone else? Or, if it is so completely and totally wrong, what are the problems with it? Or is this just one of those mind sets that we couldn't possibly be THAT close to the rest of the great apes? Kirsten. | |
| From: lentil | 19/11/99
17:13:31 |
| Subject: re: Ape/Human Evolution | post id:
8773 |
| What has testing of mitochondrial
DNA said about the relatedness of humans and other primates? Can you get
an estimate of time since divergence from
that? | |
| From: steve(primus) | 19/11/99
20:02:17 |
| Subject: re: Ape/Human Evolution | post id:
8821 |
| A.boisei and A Robustus were
bipedal having evolved from quadrupeds. Gorillas and chimps are knuckle
walkers, also having evolved from quadrupeds but not to bipedality. It is
unlikely, in the time frame, that Boisei and Robustus could have evolved
into Chimps and Gorillas. But it is a great idea. Never feel afraid to ask
such questions. Boisei, Robustus, Africanus and Afarensis are all
Australopithecines and it is more likely that some lines died out while
others evolved into homo sp. | |
| From: Dr. Ed G (Avatar) | 19/11/99
23:08:33 |
| Subject: re: Ape/Human Evolution | post id:
8871 |
| What has testing
of mitochondrial DNA said about the relatedness of humans and other
primates? Can you get an estimate of time since divergance from
that? Mitochondrial DNA doesn't recombine during sexual reproduction in the same way as nuclear DNA. As a result mitochodrial DNA is only ever inherited from the mother and it sequence only changes as the result of mutation. In this way it is much much much easier to track an individuals maternal lineage through the mitochondrial DNA. Now, the general rate of mutation is relatively constant particularly when averaged over time, and there is no evidence or reason to suggest it has changed in recent evolutionary history. Therefore, by comparing the mitochodrial DNA of two species you can get a good estimate of when they diverged from a common ancestor from the number of places in which they are different. I believe it is this technique that gives us the estimate of 5-10 million years to our common ancestor with chimpanzees. Soupie twist, Ed G.  | |
| From: Tim St. Clair | 22/11/99
0:55:29 |
| Subject: re: Ape/Human Evolution | post id:
9145 |
| Just a quick one, because I've
been browsing this site for far too long... On a related note to the topic in question... Anyone else heard of the Aquatic Ape Theory? This is quite a pet of mine - it just appeals to me, although from what I've read the evidence is quite good (two major considerations for adopting a hypothesis as dogma!). All of the books I've read on the subject were written by a journalist called Elaine Morgan: -The Aquatic Ape -The Descent of Woman -The Scars of Evolution (essentially, The Aquatic Ape updated) -The Descent of the Child My opinion? Anthropologists should study humanity as it exists now, and leave the question of when and how it arose to those more qualified, like evolutionary zoologists and molecular biologists... Ta ta for now. Flame at will, commander, Tim | |
| From: steve(primus) | 22/11/99
6:26:50 |
| Subject: re: Ape/Human Evolution | post id:
9170 |
| Anyone else heard of the Aquatic Ape
Theory? No. Care to give us a synopsis? | |
| From: steve(primus) | 22/11/99
7:25:42 |
| Subject: re: Ape/Human Evolution | post id:
9174 |
| I have heard of the Aquatic Ape
hypothesis. It is a proposal that a branch of hominids took to the water and for some tens? hundreds? of thousands of years and lived an aquatic existence before coming back on dry land to become homo sapiens. This is supposed to explain the similarities between the salt/other minerals content of our blood and seawater and also why we, of all the apes, have little body hair. It is evidently unnecessary for swimming. Also the swimming response of babies is taken as an indicator. Put a child under one year old under water, it will hold its breath and swim to the surface without fear. My own arguments against it are (1)lack of evidence (2)not enough time (3)for an aquatic existence we would need either a thick insulating coat of fur or feathers, or a thick layer of blubber, or both. The lack of hair and blubber tells me that while we might have enjoyed a dip in the sea, we weren't living in it. (4)lack of any evolutionary traits that would have made an aquatic existence easier - no webbed feet and hands for instance. (5)Food. Apes would take to the water on a semi-permanent basis only if there was a food niche to be exploited. Just about anything moving in the sea swims faster than humans so the food would not have been fish, turtles, whales, seals, squid, prawns etc. The only unmoving or slow moving sea dwellers are seaweed and some shellfish. These live, for the most part, in shallow water and would have been more easily collected from the shore and would not have required living in the water. (6) Predation. On land, hominids could run, climb trees or throw rocks and sticks at predators. In the ocean they would have no protection against anything that wanted a nibble. The only defence is to get out of the water - which argues against living in it. I can't see a aquatic ape lasting too long. Anyway, those are just my thoughts on the matter. By all means read the books and form your own conclusion. I've been wrong before. | |
| From: Kirsten | 22/11/99
10:39:07 |
| Subject: re: Ape/Human Evolution | post id:
9196 |
| Hi Dr Ed (and everyone
else), One of the reasons I was asking the question was that apparently there is some support from mtDNA for the idea - it has been found that the variation in mtDNA in humans is much lower than that in the other great apes, whereas variation in nuclear DNA is higher, suggesting selection in mtDNA (or something else going on here). But in general, sorting out the molecular clock to make it consistant across mammals and other reasonable splitting dates, then a split for humans and chimps of around 2-3 million years works. I hope that makes some sense. Kirsten. | |
| From: Kothos | 22/11/99
11:17:18 |
| Subject: re: Ape/Human Evolution | post id:
9204 |
| I've no idea about points (1) or
(2) (how much evidence or time you'd need). But; (3) I don't think the argument says we had a fully aquatic existence, only a semi-aquatic one. Compared to all the other primates, we have the beginnings of a layer of blubber (our subcutaneous fat). We most likely weren't living in the sea, the hypothesis goes that we may have been trapped in a coastal existance for a while, and started to make the transition in the same way that seals have done. (4) Only on the 'for instance' part, we do seem to have the beginnings of webbed feet and hands. Apparently the fingers of other primates are split apart right down to the knuckle, whereas we have a little flap of skin there. (5) I agree with the food thing except that since the theory calls for us being 'trapped' into existing very close to the water, we may have had no choice but to use it as a food source. (6) An aquatic ape didn't last very long, we eventually moved away again (: Whether we would have eventually completed the transition into the water (had we the time) like the dolphins have done is anybody's guess. And yes there's also the fact that dropping an infant primate into a pool makes it sink straight to the bottom, except for humans. | |
| From: Kirsten | 22/11/99
12:31:25 |
| Subject: re: Ape/Human Evolution | post id:
9219 |
| Hi Steve (primus), You were talking about Australopithecines being bipeds evolved from quadrapeds - wouldn't it be possible that the reason Chimps and Gorillas knuckle-walk is the result of starting down the biped way of life road, without being entirely successful this way, then back to knuckles as a compromise (I think there are other occurances of evolution back-peddaling...?). If not, what would be the reason for knuckle-walking rather than palms like other (quadrapedal) primates? (No I'm not having a go at anyone, just things I want to sort out in my own mind... it may all be completely wrong I'd just like to know some good reasons why). Kirsten. | |
| From: Greg | 22/11/99
12:41:09 |
| Subject: re: Ape/Human Evolution | post id:
9222 |
| We moved away from
water? Where are all major population centres usually based or the original cities founded? How are most ancient civilizations described? The Tigrus Euphrates culture, the Nile valley culture, The Indus valley culture, etc. We hang around water like ducks baby! Rivers and lakes and coasts. Sure there are Beduins and desert tribes etc on all continents but percentage-wise most of us don't stray far. Don't mention Maccu Piccu. those dudes were trying to go where no one would think of looking. I doubt we would have had a much more aquatic existence than many of us have now. Our preference in landscape.. landscape gardens, parks, golf-courses, lawns etc with small bodies of water in them probably reflects our subconscious attempt to recreate the environment we evolved in. (there's an interesting article in the current Discover magazine). We adapt our environment to suit ourselves, not the other way around. Most of our artificial environments reflect our innate aesthetic tastes (lets knock down those forests and make everything look like african savanna) usually have bodies of water or artificial streams. (Been to Versailles?) This probably is the best indication of what our ancestral landscape looked like. Open space, clusters of trees, bodies of water. A quick dip and a walk in the park. I'm off for a surf now, anyone care to join me? | |
| From: Kothos | 22/11/99
12:47:09 |
| Subject: re: Ape/Human Evolution | post id:
9224 |
Well, we moved away from the watery place where we were supposed to have been 'trapped'. But yeah it does severely look like we maintain a great preference for being close to large bodies of water. Thanks for the idea though, I might go for a dip (I'm supposed to be chucking a sicky today so I can study, but what the hell...) | |
| From: steve(primus) | 22/11/99
13:16:08 |
| Subject: re: Ape/Human Evolution | post id:
9230 |
| Among the apes, only humans are
truly bipedal. Chimps and gorillas knuckle walk to protect the palms and
fingers of the hands they use for feeding etc. Orang utans and gibbons
have extended hands and arms for brachiating (swinging through trees).
Bipedalism in apes works for those that have come out of the trees and are
using their hands more than chimps and gorillas do. Among the
Australopithecines, if they had developed bipedalism, there is no
advantage that I can see to going backwards to knuckle walking. Therefore,
leaving aside genetic variation, I think it is unlikely that
australopithecines would have been the ancestors of chimps, gorillas and
humans. Where does that place the other apes
anyway? | |
| From: Kirsten | 22/11/99
13:29:52 |
| Subject: re: Ape/Human Evolution | post id:
9235 |
| "Among the apes, only humans are
truly bipedal. Chimps and gorillas knuckle walk to protect the palms and
fingers of the hands they use for feeding etc." What about baboons - do they need to protect their hands any less? "Among the Australopithecines, if they had developed bipedalism, there is no advantage that I can see to going backwards to knuckle walking." My suggestion was along the lines that there were disadvantages to bipedalism (at least to the extent that it had developed in Australopithecines) - in humans rearanging the pelvis hasn't helped in birth (though neither has the bigger brain, so I don't know if that works as an argument). "Therefore, leaving aside genetic variation, I think it is unlikely that australopithecines would have been the ancestors of chimps, gorillas and humans. Where does that place the other apes anyway?" Even playing around with the Molecular Clock, I don't think even I can fit the orangs and gibbons in THAT close. It seemed a nice (possible) way to explain the lack of fossils for chimps and gorillas together with the (relative) excess of fossils for humans (I don't suppose that the chimps and gorillas are out there looking as hard though :-) ). Kirsten. | |
| From: steve(primus) | 22/11/99
13:45:11 |
| Subject: re: Ape/Human Evolution | post id:
9241 |
| Baboons and other monkeys are
quadrupedal for the most part - the ground dwelling ones are anyway. There
has to be an advantage in knuckle walking for the chimps and gorillas,
just as there has to be an advantage in bipedalism for humans. But, just
because two of the great apes evolved into knuckle walkers and one into a
bipedal animal, does not mean that one system of getting around is better
than the other. All it means is that at this point on the evolutionary
ladder, quadrupedalism is the best form of locomotion for baboons, knuckle
walking is the best for gorillas and bipedalism is the best for
us. Going backwards in evolutionary terms is not really on, it can only go forwards. Try Climbing Mount Improbable by Richard Dawkins. | |
| From: Kirsten | 22/11/99
14:05:46 |
| Subject: re: Ape/Human Evolution | post id:
9244 |
| With regard to your statement
about evolution not going backwards: I would like to comment that while species can't "unevolve" genetically, it is possible that a species with trait B may evolve from a species with trait A, and subsequently a species with trait A will evolve from the species with trait B. I guess this would mainly be caused by changing external conditions. I am thinking particularly about the rhabdosomes of invertebrate marine lifeforms called graptilloids (sp?), which began with very simple structures but quickly became more complex. Gradually, however, they simplified again over time. | |
| From: Kirsten | 22/11/99
14:07:10 |
| Subject: re: Ape/Human Evolution | post id:
9245 |
"Going backwards in evolutionary terms is not really on, it can only go forwards. Try Climbing Mount Improbable by Richard Dawkins." Um, already have... I have a pretty good grasp that evolution doesn't return on the same lines it's been on, my suggestion was quadruped -> biped -> knuckle-walker, 'cos it may have worked better for the chimps and gorillas (where knuckle-walking was a way to get the front limbs back on the ground (balance??)). As I also said I could be completely wrong. I think I may also have been over-reacting to the way I have been taught some of this stuff ("This is the way it is (no further correspondence will be entered into)") and also partly the general public's view that "we evolved from the apes", interpreted as "we evolved from the extant apes", when there is the possibility that in their evolutionary past they have tried and rejected something that (general public) considers a sign of superiority. Just trying to find REASONS for what is always immediately dismissed with "This is the way it is (or was)" (which may well be true :-) ). Kirsten. | |
| From: Kothos | 22/11/99
17:13:28 |
| Subject: re: Ape/Human Evolution | post id:
9308 |
| "...in humans rearanging the
pelvis hasn't helped in birth (though neither has the bigger brain, so I
don't know if that works as an argument). I would've thought the bigger brain cancelled out its influence as far as childbirth is concerned? I mean, sure it's big, but now we know how to cut people open to get around this (or is the time span too short for this to be a proper cancellation?). | |
| From: Greg | 23/11/99
1:09:29 |
| Subject: re: Ape/Human Evolution | post id:
9464 |
| Why apply value judgements to
characteristics? A return to Knuckle walking isn't a"Backward step" unless
you make the Human-chauvinistic assumption that we are a model of
perfection and organisms should naturally try to emulate us. If Knuckle
walking lets you spread your genes, Great! that's all that matters.
Natural selection is so impartial, no value judgements.Whatever works!
Mammoths' ancestors were small. When a particular population of Mammoths
were once cut off by rising sea levels they adapted into smaller forms to
less consume the resources on their islands. Reverting in size wasn't a
"backward step". The same happened to an ecosystem of dinosaus in what is
today Romania. They develloped pygmy forms.No stigma. It was simply an adaption that let the genes continue for a while longer. Cetaceans (whales and Dolphins), Penguins and Pinniped(seals), even Icthyosaurs and of course seasnakes, crocs, turtles all returned to the home of their early ancestors. P.S. Gibbons are bipedal when they are not doing the cool tarzan thing.They can run very fast on two legs and they swing their arms for balance. (Just keeping the thread going in the wee hours) | |