14:04 23 February 04 Knowing whether a pregnancy will produce a boy or girl is not left up to chance for some mammals - UK biologists claim they have conclusive proof their offspring. It has long been known that many insects, birds and fish are capable of mammals has been controversial. American biologist Robert Trivers first their physical condition at the time of conception, and the idea has been debated for the 30 years since. adjustment in ungulates - herbivorous mammals with hoofed feet - and found a consistent pattern across the different species. Sons were produced in higher numbers by mothers who were in good condition and daughters were preferentially produced by mothers in poor condition," explains Stuart West at the University of Edinburgh, who carried out the study with Ben Sheldon from Oxford University. "In ungulate species, a few strong males control a large number of females, so only a small proportion of males get to mate, whereas most of the females will mate. "Therefore high quality females were more likely to undergo the greater demands of producing sons, as the sons were more likely to be of high quality and therefore have a chance of mating. Conversely, if maternal quality was poor, the ungulates produced daughters, since poor quality daughters had a greater chance of mating than poor quality sons," he told New Scientist. Read the rest at NewScientists http://www.newscientist.com/news/news.jsp?id=ns99994708 Comment: The reason for gender selection is not, as the article seems to imply (but the paper being reported probably doesn't), by a conscious decision by the mother but by a process of natural selection (of the trait to choose) that has a benefit to the herd. The mother receives no personal benefit whatsoever by the breeding success or failure of her offspring. Where the fittest females produce males and the rest produce females the herd's survival fitness is maximised. Mothers that are not maximally fit and produce males anyway, those males are less likely to breed and so less like to father females similar to their mothers. This seems to be an example of herd or group fitness with a single natural selection component acting on individuals. Note that there is no selection pressure on fit females that produce females. Of course the pivotal word in this article is 'quality'. By what criteria is 'quality' judged? Posted by Robert Karl Stonjek.
Robert Karl Stonjek <[email protected]> wrote or quoted: > Read the rest at NewScientists http://www.newscientist.com/news/news.jsp?id=ns99994708 > > Comment: The reason for gender selection is not, as the article seems to imply (but the paper > being reported probably doesn't), by a conscious decision by the mother but by a process of > natural selection (of the trait to choose) that has a benefit to the herd. The mother receives no > personal benefit whatsoever by the breeding success or failure of her offspring. Her *genes* benefit. -- __________ |im |yler http://timtyler.org/ [email protected] Remove lock to reply.
> It has long been known that many insects, birds and fish are capable of in > mammals has been controversial. American biologist Robert Trivers first to > their physical condition at the time of conception, and the idea has been debated for the 30 > years since. its offspring is beyond me. How can the female deer control the X and Y chromosome coming from the male deer? What can the female deer do to ensure only the Y chromosome is successful and not the X? Khoon.
Red Dragon <[email protected]> wrote or quoted: > its offspring is beyond me. How can the female deer control the X and Y chromosome coming from > the male deer? What can the female deer do to ensure only the Y chromosome is successful and > not the X? I don't know what it's doing - but one possibility is selective miscarriages. -- __________ |im |yler http://timtyler.org/ [email protected] Remove lock to reply.
----- Original Message ----- From: "Tim Tyler" <[email protected]> Newsgroups: sci.bio.evolution Sent: Sunday, February 29, 2004 5:18 AM > Robert Karl Stonjek <[email protected]> wrote or quoted: > > > Read the rest at NewScientists http://www.newscientist.com/news/news.jsp?id=ns99994708 > > > > Comment: The reason for gender selection is not, as the article seems to imply (but > > the paper being reported probably doesn't), by a conscious decision by the > > mother but by a process of natural selection (of the trait to choose) that > > has a benefit to the herd. The mother receives no personal benefit whatsoever by the breeding > > success or failure of her offspring. > > Her *genes* benefit. > -- RKS: That is not a *personal* benefit. Besides, the gene combination that For a female to actually pass on her genes she would have to produce a clone. Genes that are beneficial to the male may not be beneficial to the female, but the successful female's offspring is going to get a dose of successful male's genes - some of the offspring may be superior to the parents, some inferior, and some similar (on average) as one of the two parents. offspring must fail, leaving only the offspring that actually do carry the beneficial genes. A lot of evolutionary biology thinkers seem to forget this, imagining, perhaps, some sort of magic mechanism by which only beneficial genes are passed on. Lets not forget that each parent has a diploid set of genetic material that contains expressed and possibly unexpressed genes. The beneficial genes that give the successful phenotype its appearance and behaviour are not necessarily those that are contributed by the female side, and the female allele is not necessary the one passed on to or expressed in the offspring. If the environment remains stable, then evolution effectively stops as around an adapted medium, but never become more or less adapted. Some longer necessary (a cost which produces adapted and less adapted offspring). recombination, and at least a thousand (including some lizards and fish) are Genes can not 'benefit' as such. The spreading of genes as a mark of success of that gene is a myth generated by some evolutionists who should know better. The most common form of evolutionary change is paelomorphic and permorphosic changes in offspring. This occurs when a slight variation in Hox genes causes hypermorphosis, accelerated development, predisplacement, progenesis, neoteny or postdisplacement. The dodo bird, for instance, is actually a type of pigeon that has hypermorphic beak, accelerated development of the body, and Neotenic development of the wings. Alleles are the next most common variation in offspring. New genes and the need for parents to make sure that these new genes proliferate in the offspring represent such a tiny fraction of all genetic variation in offspring that we are likely to only see it once in every few thousand years in, say, humans. In other words, new genes are extremely rare, variations are common and in the gene pool so there is no advantage to the 'successful' gene even if it does get passed on as it will likely be sharing the brood or population with many others both having and not having that gene and only chance determines whether that gene makes it through to the next generation. On the other hand, a mother not having the successful gene expressed may still have offspring that do have it as she may carry the gene but it is not expressed, or the male may carry it. Only when a change in the environment is included in the genetic inheritance equation do we get evolution happening. With a change in environment, more offspring will die and the few that survive will have the genes required to cope with the change. Thus the concentration of the advantageous genes increases in that population, the disadvantageous genes diminish until only occasional recapitulation occurs. In humans, for instance, it is rare to see genes that would have been commonly expressed in our precursor species expressed in modern times, but it has not completely stopped (but the probability of the *combination* of genes that would have made our precursor species distinct expressing in unison is negligibly small). Courtship in Nature" by James L. Gould and Carol Gould, and 'Shapes of Time: The Evolution of Growth and Development' by Kenneth J McNamara Kind Regards, Robert Karl Stonjek.
On Sat, 28 Feb 2004 18:18:22 +0000 (UTC), Red Dragon <[email protected]> wrote: >> >> It has long been known that many insects, birds and fish are capable of >in >> mammals has been controversial. American biologist Robert Trivers first >to >> their physical condition at the time of conception, and the idea has been debated for the 30 >> years since. > >its offspring is beyond me. How can the female deer control the X and Y chromosome coming from the >male deer? What can the female deer do to ensure only the Y chromosome is successful and not the X? > >Khoon. > Current views suggest that the mother's hormonal state affects whether more male or female zygotes implant in her uterus. William L Hunt
"Tim Tyler" <[email protected]> wrote in message news:[email protected]... : Red Dragon <[email protected]> wrote or quoted: : of : > its offspring is beyond me. How can the female deer control the X and Y : > chromosome coming from the male deer? What can the female deer do to ensure : > only the Y chromosome is successful and not the X? : : I don't know what it's doing - but one possibility is selective miscarriages. : -- : __________ : |im |yler http://timtyler.org/ [email protected] Remove lock to reply. Wasn't there supposed to be some mobility differences in the sperm in various pH levels? Could the health of the female deer made a difference Jois
