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Author Topic:   The race issue
extremophile
Member (Idle past 5595 days)
Posts: 53
Joined: 08-23-2003


Message 33 of 134 (489965)
12-01-2008 1:28 AM
Reply to: Message 1 by IceNorfulk
02-19-2008 1:18 PM


quote:
How do you account for the skull differences and cranial makeup within the races? For example, a Negro and Caucasian skull -
Yahoo
How could the skull on the right turn into the skull on the left within only 3,000 years?
Just one thing. These skulls in the picture are not from a white and a black person.
At least judgin by this image with the same file name, from another source:
But anyway. Dog breeds changed quite more dramatically in less time. Extremely masculinized and feminilized skulls can reach comparably similar difference in "no time". Just for comparison.
There are also some recent cranial changes that are not result of genetic evolution per se, but from "evolution" on the foods we eat. Cooked food is easier to chew, this results in smaller jaws and muscles. It was also replicated with experiments with animals.
Other alimentary differences, affecting nourishment, can also affect the skull without any genetic change. This does not mean that all the changes within skull shapes on the human species are due to that; besides the most obvious guesses, like differences between europeans, africans and asians, there are differences within each continent that are also really rooted in genetic variations.

This message is a reply to:
 Message 1 by IceNorfulk, posted 02-19-2008 1:18 PM IceNorfulk has not replied

Replies to this message:
 Message 34 by anglagard, posted 12-01-2008 3:53 AM extremophile has replied

  
extremophile
Member (Idle past 5595 days)
Posts: 53
Joined: 08-23-2003


Message 35 of 134 (490100)
12-02-2008 10:22 AM
Reply to: Message 34 by anglagard
12-01-2008 3:53 AM


Re: Huh?
It's not lamarckian neither lysenkoian. I should have explained it better. The bone development is somewhat like muscle development, it's sensitive to strains. Tennis players, for instance, have asymmetrical bone widths and densities on their arms. It's more significant before complete maturation, after that, it's more subtle, but still exists (hence physicians recommending exercise to prevent or even reduce osteoporosis).
quote:
Effects of food processing on masticatory strain and craniofacial growth in a retrognathic face
Auteur(s) / Author(s)
LIEBERMAN Daniel E. (1) ; KROVITZ Gail E. (2) ; YATES Franklin W. (1) ; DEVLIN Maureen (1) ; CLAIRE Marisa St. (3) ;
Résumé / Abstract
Changes in the technology of food preparation over the last few thousand years (especially cooking, softening, and grinding) are hypothesized to have contributed to smaller facial size in humans because of less growth in response to strains generated by chewing softer, more processed food. While there is considerable comparative evidence to support this idea, most experimental tests of this hypothesis have been on non-human primates or other very prognathic mammals (rodents, swine) raised on hard versus very soft (nearly liquid) diets. Here, we examine facial growth and in vivo strains generated in response to raw/dried foods versus cooked foods in a retrognathic mammal, the rock hyrax (Procavia capensis). The results indicate that the hyrax cranium resembles the non-human primate cranium in having a steep gradient of strains from the occlusal to orbital regions, but differs from most non-anthropoids in being primarily twisted; the hyrax mandible is bent both vertically and laterally. In general, higher strains, as much as two-fold at some sites, are generated by masticating raw versus cooked food. Hyraxes raised on cooked food had significantly less growth (approximately 10%) in the ventral (inferior) and posterior portions of the face, where strains are highest, resembling many of the differences evident between humans raised on highly processed versus less processed diets. The results support the hypothesis that food processing techniques have led to decreased facial growth in the mandibular and maxillary arches in recent human populations.
http://www.fas.harvard.edu/~skeleton/pdfs/2004b.pdf
And a parallel comment on the lamarckian inheritance thing. Despite stronger concepts of "lamarckian" inheritance being obviously wrong, there are indeed some effects of the progenitor's conditions and "acquired traits" on the offspring. It won't be always like parent "develops X, offspring develops X", neither always adaptive, but it happens. Other big difference from classical notion of inheritance of acquired traits is that it tends (as far as I know) to be reasonably short-lived. It does not affect the genes, so, theoretically, with a different growing environment for the offspring, the next generation would likely be "reset" back ti its "genetic default". But it may have "cyclical" effects too, like the change on the offspring development increasing the probability of the same circumstance happening with the offspring.
It won't, however, have an effect such as lengthening the giraffe's neck; it's much less dramatic. Stretching the possibilities to the most, it would be something like bonobos differences from chimps evolving largely due to positive feedback loops on social environment and behavioral changes that happened without genetic contribution, but maybe by an accident, such as most despotic adult males dying for some reason, resulting in a group formed mostly by comparatively docile females and their developing offspring (something similar is reported to have happened with a baboon tribe). But as far as I know, no one actually theorizes that it was the case; it was just an exaggerated example.
A real example would be that children born from malnourished parents have a tendency to obesity, more or less as if the developing baby's body on the womb were inferring that these are tough times out there, and he/she needs to be avaricious with the resources.
More on the scope of the previous post, children of highly stressed parents will have smaller cranial circumference and some brain changes reflecting the stress or depression (as some stress-related hormones trespass the placenta). The later has no adaptive value at all, as far as I can think of. The previous can be somewhat adaptive, but it's not "like father like son" type of lamarckian inheritance, but instead, "overly thin parents, possibly obese children".
Edited by extremophile, : grammar
Edited by extremophile, : grammar and etc

This message is a reply to:
 Message 34 by anglagard, posted 12-01-2008 3:53 AM anglagard has replied

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