the liver and the brain

dan michaels feedbackdroids at yahoo.com
Sun Sep 5 14:27:24 EST 2004


r norman <rsn_ at _comcast.net> wrote in message news:<0b4mj0p65jiodagsip98lfl6ph59uiq405 at 4ax.com>...

> >http://www.stanfordalumni.org/birdsite/text/essays/Precocial_and_Altricial.html
> >
> >TYPE OF DEVELOPMENT DOWN PRESENT? EYES OPEN? MOBILE?. FEED.SELVES?
> >PARENTS ABSENT? EXAMPLES
> >Precocial 1 Yes Yes Yes Yes Yes Megapodes 
> >Precocial 2 Yes Yes Yes Yes* No Ducks, Plovers 
> >Precocial 3 Yes Yes Yes Yes No Quail, Turkey 
> >Precocial 4 Yes Yes Yes Yes/No No Grebes, Rails 
> >Semi-precocial Yes Yes Yes/No No No Gulls, Terns 
> >Semi-altricial 1 Yes Yes No No No Herons, Hawks 
> >Semi-altricial 2 Yes No No No No Owls 
> >Altricial No No No No No Passerines 
> >...
> 
> Many posts ago, I did refer you to the Megapodes, including the
> partridges, pheasants, and quail.  These are fully independent at
> birth and therefore at hatching have well developed sensory, motor,
> and integrative centers that clearly are genetically determined.  That
> ducks are highly precocial does not mean that learning, as in
> imprinting, is not important in their early life.  It simply means
> that there is a genetically determined system that requires a learned
> component to be implemented fully.  I thought the whole trend in this
> discussion is that there is no absolute distinction that can be made
> between learning/environment/nurture and instinct/genetic
> determinism/nature.  In many cases, probably in virtually all cases
> for mammals and primates, they interact.


Yes, no doubt they interact. What's of interest to me is the
"relative" balance regards nature vs nurture in the groups, esp
precocial. The relative balance must swing somewhat different ways in
the 2 types - and no doubt depending upon the characteristics one is
looking at, such as motor versus perception, etc.
One imagines a baby chick has some degree of built-in ability to
distinquish mother and other chicks from predators such as foxes, as
those species which did not have this would likely have gone extinct
long ago.

This N.v.N thing is obviously a spectrum, with a lot of animals down
on the nature/instinct end, and a general trend towards greater
importance of nurture on the other end. If you look at it this way, it
seems a waste of time to argue absolutes of "nature vs nurture",
rather it seems more fruitful to figure out about where on the
spectrum various animals would lie. In addition, you probably need
several such spectrums, or scales, in order to cover different
attributes ... motor, perceptual, etc ... as there is no doubt some
differential placement regards each.

Back to perception, it's actually not too hard to hypothesize the
existence of neural circuitry for distinquishing predators from prey
[or self-same species]. Frogs already have the basis of this in their
class 3 and 4 retinal cells. One imagines precocial animals rely on
something similar, albeit more sophisticated.



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