Re: EVOLUTION: The Aquatic Ape

Keith Henson (
Thu, 23 Jan 1997 16:31:28 -0800 (PST)

On Thu, 23 Jan 1997, Jay Reynolds Freeman wrote:

> A couple of points on throwing things:
> Some of the stuff about trajectory computation, release timing,
> and so on, was possibly well developed long before Lucy and her kin.
> They likely stemmed from arboreal predecessors, who had occasion to
> leap around in the treetops, in the manner of modern monkeys: Missing
> the branch you jump for has low survival value. A variety of
> present-day arboreal animals with much smaller brains than Lucy handle
> projectile-hurling over distances of several meters tolerably well --
> they themselves being the projectiles. The common local example is
> (*ahem*) squirrels.

For some reason, perhaps the lenght of time this behavior has been
wired into the nervous system, I think body motions may take less
computation, or perhaps I mean the computation is more distributed.
Accurate throwing takes accurate motion sequencing, and the motion
is over in too short a time to get corrective feedback, i.e., the
whole thing is driven off a sequencer located in the (?) pre-motor

> There is a subtle point on using weaponry to drive off predators
> that may not have come up yet. To defend against a predator does not
> require that one kill or injure the predator, or even that one have a
> particularly high probability of doing so. It merely requires that
> one make the risk to the predator, of pressing home an attack,
> unacceptable.

Excellent points. Dogs fear rocks, even if the chances of one being
seriously hurt by a rock are not high (though once I knocked a dog out
with a thrown object). Chimps throw things at preditors today, and this
might well have been the origin of a preditor discoraging method used by
Lucy and Co. Projectiles hitting lions or similar at a distance might
trigger the idea that if they are being hurt this far out, getting closer
is a really bad idea. Of course, being bipedal makes it a lot easier to
throw things, so the possiblity exist that being being ready to throw was
important enough to make a difference. Rocks moved by people (manuports?)
are older than chipped rocks I think, but I don't have a reference at

> Consider an hypothetical predator that takes one large animal-prey
> per week, that starts doing so at age six months, and that attains
> sexual maturity some time between two and three years of age. That's
> 100 prey encounters before the animal gets a chance to pass on its
> genes. Even an encounter with prey whose only immediate effect is to
> injure the predator, may result in its subsequent death, either from
> starvation because of reduced ability to hunt, or from being preyed
> upon. Thus if the average risk of even moderate injury, per prey
> encounter, is as high as one percent, it is more than likely that the
> predator will be out of the gene pool before reproducing.
> Hence, as long as there are alternate prey animals, it doesn't
> take a highly lethal defense to deter predators. We have the
> situation, paradoxical at first sight, that even a prey species that
> would be very likely to lose in a fight to the death with a predator,
> may be able to deter that predator by virtue of the small chance of a
> different outcome. After all, the predators aren't out for fights to
> the death as such, all they want is lunch.
> -- Jay Freeman, First Extropian Squirrel

Good points. Keith Henson