rsd@sei.cmu.edu (Richard S D'Ippolito) (04/06/89)
In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes:
= I think you're really mincing words here: selection is
=selection. Try this: environmental pressure upon a species will be
=more beneficial towards certain individuals, due to an advantageous
=trait. For example: a giraffe with a long neck can eat all the leaves
=that a giraffe with a short neck can eat, plus more leaves out of the
=latter's reach. This pressure would give this giraffe a better chance
=to survive and rear its young; therefore adding "long-neckedness" to the
=giraffe's gene pool.
I've tried that before, and it doesn't go down well. Please provide us with
the definitive process implied by the word "therefore" in your last
statement. Thanks.
Rich
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Ideas have consequences. RSD@sei.cmu.edu
Richard Weaver
---------------------------------------------------------------------------sabol@Apple.COM (Bryan Sabol) (04/06/89)
In article <3144@ae.sei.cmu.edu> rsd@sei.cmu.edu (Richard S D'Ippolito) writes: >In article <28379@apple.Apple.COM> sabol@Apple.COM (Bryan Sabol) writes: > >= I think you're really mincing words here: selection is >=selection. Try this: environmental pressure upon a species will be >=more beneficial towards certain individuals, due to an advantageous >=trait. For example: a giraffe with a long neck can eat all the leaves >=that a giraffe with a short neck can eat, plus more leaves out of the >=latter's reach. This pressure would give this giraffe a better chance >=to survive and rear its young; therefore adding "long-neckedness" to the >=giraffe's gene pool. > >I've tried that before, and it doesn't go down well. Please provide us with >the definitive process implied by the word "therefore" in your last >statement. Thanks. "Definitive process", huh? Here goes nothing: referring back to the aforenoted article, the idea is that variance in individuals of a population may become beneficial or detrimental, depending upon how environmental pressure relates to an attribute. If one individual giraffe has a longer neck than another and there is a limited amount of leaves available in the population's range, then individuals who have longer than average necks would be able to eat all the leaves of ones with shorter necks, and also be able to eat ones higher up. The "therefore" comes into play here: if such a shortage exists, then individuals who can obtain more food would tend to have a better survival rate (yes, I know there are a multitude of factors concerned with "survival", but I'm trying to keep this shorter than a novel) than the other individuals with shorter necks in the population. If these animals were more "successful" (another dangerous term: here I mean this as the equivalent to "survivability"), their offspring would have a better chance to retain such an anatomical feature as a long neck, and would have a relatively similarly higher survival rate as did their parents. Assuming that the environmental pressure (in this case, limited availability of leaves) continues to place importance on obtaining leaves high-up in the trees, then over time, more long-necked individuals would survive to birth their offspring; and the offspring with longer necks would also survive to bear young, until the population, i.e., gene pool would have a higher rate of long-neckedness expressed than before. I also just received a note from someone who used better (and more concise!) terminology than I in this area; I think his definition may be as accurate as you requested. I hope Erik thinks it's ok for me to post this...apologies given already if otherwise: ++++++++++++++++++++++++++++++++++++ From sabol Wed Apr 5 09:03:43 1989 To: eao@cs.umu.se Subject: Re: The birds and the beaks Status: RO [from eao@cs.umu.se] >"therefore adding ... to the gene pool" is a rather strong assumption given the >understanding of inheritance Mendel gave us through his works. >Environment defines possible species, some of which have long necks, some >of which have not. How the gene pool adapts to this environment is an open >question (LaMarck/Darwin/?/??/...). ++++++++++++++++++++++++++++++++++++ I agreed with him; mostly I didn't want to spend a large amount of time on this aspect, but it seems to have brought up more debate. Ergo, my ammeded definition. However, I reponded to his statement as follows: ... >But looking back at the original focus of this discussion, the >question of why birds have beaks remains. In this case, I absolutely >agree with your statement that "environment defines possible >species....and How the gene pool adapts to this environment is an open >question". But in this specific case, we have more than theory to use >as a tool: the skeletons of _archaeopteryx_ show an organism in a >transitionary state, who seems as much a reptile as a bird (at least >it's the best note of feathers outside of later true birds). If I remember >the skeletal structure of _archaeopteryx_ correctly, its skull did not >have a beak; it had a true jaw, and many teeth. So there is an organism, >who has the unique characteristic of feathers, but has not yet developed >the beak. Adding this information with the knowledge that all birds >have beaks, can't we propose that the gene pool's successful adaptation to >the environment was the development of the beak? Whew! If you haven't already "k'd" this article, thanks for bearing with me. Other ideas, folks? bryan sabol ousted reedie-at-large