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Repost On Predation... Re: Aquatic ape theory
Thomas Clarke (clarke@acme.ist.ucf.edu)
27 Oct 1995 15:18:43 GMT
Yes, I did save J. Moores Sep 25 repost.
Let me go through it and point out where I find the
argument unconvincing. This will save him
having to repost yet again.
JM> From: J. MOORE
JM> Date: 07-01-95
JM> Subj.: On Predation...
JM>
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.
OK.
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.
Yes. This is a truism.
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.
OK. Chimps are still around as a species so predation had to be less
than the replacement rate.
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.
Here is where you loose me. "numerous, vicious" is pretty vague.
How numerous? Need to quantify.
How vicious? My experience is that alligators will attack bite
sized things like small dogs, but the circumstances have to be
unusual for larger animals to be attacked.
The water born predators are also dumber than the mammalian land
predators. I don't see any great problem in avoiding them.
Much of course depends on exactly how the proto-hominids interacted
with the water. That should be the subject of debate.
Your argument at best eleminates versions of the AAS where the
apes spend continuous amounts of time in water frequented by crocodiles.
That is they could not have lived an otter-like lifestyle.
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.
What is this about? Are you comparing ape mammals to crocodile reptiles?
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.
Yes people are occassioally killed by lions, and bears, and sharks and
crocodiles, and snakes, and spiders, and ...
Do you have quantitative figures for death by crocodile versus death
by land predator? Indians lived in Florida successfully before Columbus.
I don't see the problem.
Life is dangerous, the world is full of predators, both on land, sea, and
air. If chimps can cope with cats and snakes, I don't see why australopiths
can't cope with crocs.
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
JM> problem.
So they stay out of the water when necessary. Good time to go look
for fruit.
This summer I stayed at the Wakula Springs Lodge near Tallahassee.
A state park, the lodge includes a swimming area on the Wakula river
where kids come to play. I took a tour boat ride on the river and
was somewhat surprised to see, not 50 yards from where the kids were
diving off the dock, alligators sunning themselves on the shore.
I guess they weren't hungry or that young H.s wasn't their favorite food :-)
Oh, there were no adults with rifles guarding from the shoreline..
JM> A couple of further notes: when we compare the birth rates of
JM> chimpanzees and of modern humans who gather and hunt, we find that
JM> their birth rates are rather low compared to a great many other
JM> mammals. Even whales, sea otters, and other marine mammals, which
JM> generally have only one offspring at a time, breed faster -- both at
JM> an earlier age and with much faster infant development, and less
JM> time between kids.
That's why the Australopith water would slap the hell out of the kid
it went near the water without an adult ... The adults have behaviors
that help maximize the young's probability of survival.
Tom Clarke
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