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On Predation...
J. Moore (j#d#.moore@canrem.com)
Sat, 1 Jul 95 18:34:00 -0500
On The Problem of Predation:
We've had a few varying threads on the subject of predation on early
hominids, specifically the transitional population, and in light of some
of the responses, I thought I'd make some points.
One is that predation happens, sometimes. It doesn't matter much
*unless* there's too much of it. When the animals can't at least
replace their population, there's a problem. Populations may get
smaller for a while, and often do, but if a population goes year after
year without being able to replace its numbers, it can't last.
Another is that, for the transitional population, we can surmise, from
fossil and molecular evidence of relatedness, an animal that is similar
in mental and physical abilities to chimpanzees, and so can use that
species' proven ability to survive in open savannah woodland as a model
for how our ancestors could've done the same. We can even see *how*
they might have handled land-based predators, based on how chimps do so
now. We can also see that predators such as snakes, both constrictors
and venomous, are apparently not a problem for chimps today, and
therefore likely would not have been a fatal problem for the
transitional population, although you could expect all such predators
might occasionally have been a fatal problem for some individuals.
We have a problem in doing this for a proposed water-based transitional
hominid population. They would've faced water-based predators which,
as has been shown in previous posts, are numerous, vicious, and do not
respond to bluff and even counterattack as readily as do land-based
mammalian predators. We also have no appropriate model for such a
water-based hominid. Animals which have survived in this environment,
spending many hours a day in the water, are either quite large or breed
prodigiously. Even animals such as African otters have several pups
each year and these pups are self-sufficient by the following year.
This means they are having a lot more young than would the transitional
hominids. This also means the population can afford to lose more of its
members than could the transitional hominids.
The point is that avoiding all predation isn't what's needed, just
avoiding *enough* predation. What "enough" is depends on how many kids
you've got to spare. In my recent reading on crocodilians, for example,
they have a high mortality rate until they reach, for Nile Crocodiles,
about a meter in length. The first year mortality may be as high as
90%, and some mortality occurs even later. But overall, even as the
mortality rate climbs to as much as 98%, there is still a surplus in the
population, because they start with 50 eggs or so (up to 80), and have a
long reproductive lifespan. Many fish, of course, lay thousands of aggs
each year, and manage to keep a surplus despite heavy losses throughout
the lifespan. Even animals which just one, two, or three offspring each
year may do well enough if those kids mature quickly. Hominids, like
apes, had a different problem. They just didn't have that many kids, and
couldn't afford to lose many.
One other thing is what we can tell from the records of predators and
modern human populations. One thing we *can't* say is that these
predators were not a problem because they don't kill most of the human
population today. We have a population that is obviously not all
spending 4-8 hours a day in predator-filled water, and furthermore, we
have very sophisticated devices and weaponry to help deal with these
predators in places we might encounter them. Early hominids not only
didn't have shark nets and firearms, or even steel knives and spears,
they also didn't even have sharpened rocks until some 4-6 million years
after the transition had occurred. And yet we *can* see that, even with
these modern weapons, we still have *some* problems with large predators.
And in the case of the most common and likely predator of an African
water-based transitional hominid, the crocodile, we can see that, when
they get hold of humans today, even when other humans fight them with
modern spears and knives, these counteroffensive tatics are ineffective.
We know how chimpanzees, so alike in mental and physical abilities to
our early ancestors, handle land-based predators, and we know that they
have been effective enough at doing so to survive in the presence of
these predators. We also know that we do not have effective measures
against water-based predators even today (other than staying out of the
water), and have no appropriate, applicable model for our ancestral
population which shows us an effective strategy for dealing with this
problem.
Jim Moore (j#d#.moore@canrem.com)
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