On Predation... Re: Aquatic ape theory
J. Moore (firstname.lastname@example.org)
Wed, 27 Sep 95 11:08:00 -0500
Ss> 1) I will concede there were vicious predators that
Ss> decimated the numbers of "early humans" living in
Ss> the aquitic environment.
Ss> 2) You will concede that sufficient numbers survived
Ss> to continue their species.
Ss> All of which is reasonable to assume from the models of
Ss> predator-prey demographics.
The problem lies in conceding point 2 without any evidence that it
should be conceded. Here is something I previously posted (from
July 95) on the general problem of predation. The essential
problem is that we have a model (in chimpanzees) with similar
"predator-prey demographics" and similar reproductive rates
surviving in a land-based environment. We have no such model for
an aquatic environment, which means that your point 2 is not
"reasonable to assume".
JM> From: J. MOORE
JM> Date: 07-01-95
JM> Subj.: On Predation...
JM> On The Problem of Predation:
JM> We've had a few varying threads on the subject of predation on early
JM> hominids, specifically the transitional population, and in light of some
JM> of the responses, I thought I'd make some points.
JM> One is that predation happens, sometimes. It doesn't matter much
JM> *unless* there's too much of it. When the animals can't at least
JM> replace their population, there's a problem. Populations may get
JM> smaller for a while, and often do, but if a population goes year after
JM> year without being able to replace its numbers, it can't last.
JM> Another is that, for the transitional population, we can surmise, from
JM> fossil and molecular evidence of relatedness, an animal that is similar
JM> in mental and physical abilities to chimpanzees, and so can use that
JM> species' proven ability to survive in open savannah woodland as a model
JM> for how our ancestors could've done the same. We can even see *how*
JM> they might have handled land-based predators, based on how chimps do so
JM> now. We can also see that predators such as snakes, both constrictors
JM> and venomous, are apparently not a problem for chimps today, and
JM> therefore likely would not have been a fatal problem for the
JM> transitional population, although you could expect all such predators
JM> might occasionally have been a fatal problem for some individuals.
JM> We have a problem in doing this for a proposed water-based transitional
JM> hominid population. They would've faced water-based predators which,
JM> as has been shown in previous posts, are numerous, vicious, and do not
JM> respond to bluff and even counterattack as readily as do land-based
JM> mammalian predators. We also have no appropriate model for such a
JM> water-based hominid. Animals which have survived in this environment,
JM> spending many hours a day in the water, are either quite large or breed
JM> prodigiously. Even animals such as African otters have several pups
JM> each year and these pups are self-sufficient by the following year.
JM> This means they are having a lot more young than would the transitional
JM> hominids. This also means the population can afford to lose more of its
JM> members than could the transitional hominids.
JM> The point is that avoiding all predation isn't what's needed, just
JM> avoiding *enough* predation. What "enough" is depends on how many kids
JM> you've got to spare. In my recent reading on crocodilians, for example,
JM> they have a high mortality rate until they reach, for Nile Crocodiles,
JM> about a meter in length. The first year mortality may be as high as
JM> 90%, and some mortality occurs even later. But overall, even as the
JM> mortality rate climbs to as much as 98%, there is still a surplus in the
JM> population, because they start with 50 eggs or so (up to 80), and have a
JM> long reproductive lifespan. Many fish, of course, lay thousands of aggs
JM> each year, and manage to keep a surplus despite heavy losses throughout
JM> the lifespan. Even animals which just one, two, or three offspring each
JM> year may do well enough if those kids mature quickly. Hominids, like
JM> apes, had a different problem. They just didn't have that many kids, and
JM> couldn't afford to lose many.
JM> One other thing is what we can tell from the records of predators and
JM> modern human populations. One thing we *can't* say is that these
JM> predators were not a problem because they don't kill most of the human
JM> population today. We have a population that is obviously not all
JM> spending 4-8 hours a day in predator-filled water, and furthermore, we
JM> have very sophisticated devices and weaponry to help deal with these
JM> predators in places we might encounter them. Early hominids not only
JM> didn't have shark nets and firearms, or even steel knives and spears,
JM> they also didn't even have sharpened rocks until some 4-6 million years
JM> after the transition had occurred. And yet we *can* see that, even with
JM> these modern weapons, we still have *some* problems with large predators.
JM> And in the case of the most common and likely predator of an African
JM> water-based transitional hominid, the crocodile, we can see that, when
JM> they get hold of humans today, even when other humans fight them with
JM> modern spears and knives, these counteroffensive tatics are ineffective.
JM> We know how chimpanzees, so alike in mental and physical abilities to
JM> our early ancestors, handle land-based predators, and we know that they
JM> have been effective enough at doing so to survive in the presence of
JM> these predators. We also know that we do not have effective measures
JM> against water-based predators even today (other than staying out of the
JM> water), and have no appropriate, applicable model for our ancestral
JM> population which shows us an effective strategy for dealing with this
A couple of further notes: when we compare the birth rates of
chimpanzees and of modern humans who gather and hunt, we find that
their birth rates are rather low compared to a great many other
mammals. Even whales, sea otters, and other marine mammals, which
generally have only one offspring at a time, breed faster -- both at
an earlier age and with much faster infant development, and less
time between kids.
Jim Moore (email@example.com)
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