Re: Dissecting the Aquatic Ape: Bipedalism

31 Jul 1996 13:09:26 GMT

Leonard Timmons ( wrote:
: HARRY R. ERWIN wrote:
: > Behavioral features can change much more quickly than phenotype.
: > Behaviorally based speciation can take as little as 1000-2000 years.
: > (Cichlids in Lake Nabunago, fruit flies in Hawaii.) Why this occurs is
: > interesting, involving how learning and selection interact in defining an
: > ESS. I have an old paper on the subject from back when I was doing ESS
: > theory (1980-1990).

: I can understand approx 90% of what you folks are talking about, so bear
: with me. (ESS?)

Evolutionarily stable strategy--one resistant to replacement by other

: My understanding is that hominid evolution was quite rapid as the
: evolution of species go. However, I was unaware that the rapidity of that
: change was a possible argument for it being behavorially caused. My
: understanding of chimpanzees is that they have the rudiments of a culture
: and that the culture can change from group to group. If our distant
: ancestors had cultures too, isn't trying to predict the behavorial basis
: of their speciation very, very, problematic?

Oh yes, except that we have evidence for very slow cultural change until
about 110 KYr BP.

: If, however, we assume that hominid evolution occured as the result of some
: learned behavior, then that event should probably be something that was
: discovered accidentally and perpetuated through imiation and teaching. It
: would have to become a part of the new culture. To me, the question of
: bipedalism is a question of what changes in protohominid culture caused
: bipedalism (and other structural changes that occured near this time) to
: be a successful survival strategy.

: In your answer, keep in mind that I know the meanings of a lot, but not all,
: of the jargon that you use.

: In line with this, I have been nursing a theory for a few years that I would
: like someone to pass on. (This might be very amateurish, however.)

: I have noted that among most species, when males fight they try to determine
: one another's ability to inflict damage without actually doing so. I have
: heard of the survival advantages to this strategy and thus the reason for
: its evolution. However, when I look at us and our ancestors, I see animals
: that are just about completely unarmed. We cannot really inflict damage on
: one another of the same magnitude as one horned animal goring another. I
: don't know why we lost our incisors, but the prevalance of alliances among our
: ancestors may have eliminated even these (I guess).

This game is chaotic, by the way, if the strategies are learned. It
converges rapidly to an ESS if learning is not important.

: One of the things that I noted in Ms. Goodall's book _In the Shadow of Man_,
: is the difficulty that a group of chimps had in killing another individual
: even when he was alone and outnumbered. The attacks were brutal, inefficient,
: and prolonged. I remember thinking to myself, that I didn't remember reading
: anywhere about the evolutionary consequences of two animals who fight, but
: one is always killed and the other always unharmed (or only trivally so).
: It seemed to me that the evolutionary consequences of such a situation would
: be significant. In fact, I thought that such a situation must be somehow
: unstable -- and that is why I had never heard it discussed.

See above.

: To me, in order for this situation to exist, the two animals would have to
: be nearly completely unable to harm one another. This seemed possible for
: our ancestors in light of the accounts of the attacks above. However, at
: some point our ancestors would have discovered how to quickly and efficiently
: kill a rival and almost always remain unharmed. In my mind this would
: cause a rapid spurt of evolution until the situation was corrected.

Fitness is defined in relative terms. If the interpersonal behavior
within a specific group became deadly, the group would disappear.

: So I asked myself, "In what way could one protohumanoid learn to kill another
: protohumanoid and be spared in the vast majority of cases?" My answer was
: that this could be done by strangulation. This is a learned behavior and
: can probably be taught to chimps today. It could easily be taught to others,
: and the victor, if not severely bitten, would be essentially unharmed. To
: avoid the bite would require stealth, which we already see in chimps and
: would certainly be a part of the behavior of our ancestors.

The mechanism by which victims were selected would evolve chaotically.
Anything that increased the mean death rate would reduce fitness, and the
group would soon disappear to the hell reserved for homicidal maniacs.

: What I like about this theory (and I admit that this is speculation) is that
: in order to become good at strangulation the body plan of an ancestral ape
: would have to change significantly to accomodate this behavior. If we assume
: that the attacking ape was to the rear of the victim, in close contact, with
: his arm around the neck, he would just have to hold on for four minutes or so
: to be free of a rival. The successful attacker would be taller and able to
: suspend his victim from the ground. The ultimate is probably being able to
: stand up and lean backward and maintain balance while holding the victim above
: the ground. Bipedalism may be a consequence of adapting to this requirement.
: The loss of hair might also aid the attacker.

The group would quickly learn of the threat and would deal with it.

: The successful victim would also require strucural changes to the head and
: neck that would tend to defeat the strangulation attempt. Clearly a shorter
: snout would be of some advantage. However, of even more advantage would be
: the ability to call for help. With a restricted airway, the ability to
: produce fricatives would be _very_ nice. It is my understanding that chimps
: are, and maybe our predecessors were, unable to produce these sounds. No one
: knows the basis for their evolution in humans.

: In time, an entire culture might rise to enable one to survive person to
: person combat more effectively. This would include wrestling matches, etc.
: I mention this because, such combat in the form of wrestling is the oldest
: form of sport. Stylized versions have evolved, though. It might even be
: possible to assert that physical changes in humanoids were caused by
: wrestling (or other person to person combat training) until recent times (HSS).

: Anyway, since this is really (hopefully informed) speculation, I am just looking
: for someone to tell me if this sequence has any major flaws in it. Or does it
: hold together fairly well as an event that could cause the rise of mankind.

See comments above.

Harry Erwin, Internet:, Web Page:
49 year old PhD student in computational neuroscience ("how bats do it" 8)
and lecturer for CS 211 (data structures and advanced C++)