Re: Multi-age Broods. Ignorance or Apathy?
Paul Crowley (Paul@crowleyp.demon.co.uk)
Wed, 14 Aug 96 20:25:31 GMT
In article <3210D49C.3CB7@dircon.co.uk>
jdwaters@dircon.co.uk "John Waters" writes:
> 3. More important from an evolutionary point of view is the L.B.I.
> multi-age brood. This is the kind of brood found in hunter-gatherer
> tribes. Generally there is a birth interval of four years in this type
> of brood. As Apes are gatherer-hunters, it is generally thought that
> hominid ancestors were either gatherer-hunters or hunter-gatherers.
This reasoning is weak. The differences between hominids and apes
are too great for the analogy to work. As I see it, the speed of
hominid evolution was so rapid that any mechanism that helps to
explain it must be considered seriously. If famines were common
then those hominids which were able to re-populate most quickly
would soon predominate. If the ecology permitted it, a population
would quickly adopt short birth intervals in preference to long ones.
Behaviours inherited from the apes would rapidly be lost. Hominids
would switch from "K" to "r" rates of breeding. The "K" pattern
seen in traditional gatherer-hunters in simply a response to a
stable ecology. They have little trouble adapting to "r" rates
when they tap into welfare provided by the industrial state.
The mechanism is simple: when the food supply is good, infants are
weaned from the breast more quickly and the female becomes fertile
again.
> 5. It should be noted that the multi-age brood characteristic could only
> be maintained by a specie with pre-adapted advanced infant rearing
> characteristics. These pre-adaptions were caused by long term biological
> selection of improved infant rearing characteristics due originally to
> changes in the head-to-body ratio of the specie. Such changes increased
> the period of infant helplessness after birth.
I follow all this -- although I disagree with it -- it's the
standard doctrine. (Read it very slowly, expand each clause, and
see if it still makes sense.)
> This created the
> evolutionary pressure for more advanced maternal responses, including
> (as you have surmised) bipedalism.
But I don't follow this. Bipedalism was there at 4.4 mya; if
infant "big heads" ever arrived (and I question it - compare newborn
chimps/gorillas with newborn Hss) they didn't come until about 2 mya.
Paul.
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