its not just genetic inability to mate. its also social. For example, bobcats will and still sometimes DO sucessfully mate with housecats with non mule offspring. but they generally do not, from a social standpoint. Darwins finches that speciated apart did so in large part not because of genetics, but because as they found different niches to feed in from teh changing bills, they simply were in different areas of the islands. Mud stabbing bug eaters just never associated with wide billed nutcrackers. doesn't meant that if you artifically changed their environments they COULDN'T possibly end up mating, they just don't.
On Tue, May 26, 2009 at 3:14 AM, Horace Heffner <hheff...@mtaonline.net> wrote: > > On May 24, 2009, at 2:07 PM, mix...@bigpond.com wrote: > >> In reply to Horace Heffner's message of Sun, 24 May 2009 01:03:41 -0800: >> Hi, >> [snip] >>> >>> The distinguishing characteristic is the inability to mate with >>> the parents, or at least with some of the animals the parents can >>> mate with, which can be due to a genetic characteristic that does not >>> manifest in a visible way. >> >> Agreed this is the definition of species. >> >>> In any case I don't think speciation >>> occurs in a single birth, but rather as a gradual migration of >>> combined traits through a population. Speciation often occurs due to >>> the geographical separation of populations of a single species. If a >>> single birth occurred of an animal unable to mate with any others, >>> then that new species would have no future because it would need >>> others of its kind with which to mate. >> >> This appears to lead to a problem with regard to the definition of >> species. >> >> In short how can any new species exist if it can't mate, and if it can >> mate, >> then it is not a new species. We seem to have a paradox. > > No paradox is necessary - provided speciation occurs gradually in a large > population. It seems to me likely that the *probability* of offspring due to > genetic feasibility must change gradually throughout a population as > mutations occur through time. > > It seems to me also true the probability of mating itself may change due to > mutations, and this is a form of of natural selection. The gradual > development of an appearance change amongst a sub-population of a species > could gradually isolate that group genetically, even though it is not > isolated geographically. > > Speciation is likely the combined effect of many mutations, and > sub-populations along the way might be less likely to produce offspring when > mated with each other. The larger the number of mutations, the less the > probability of offspring. I think even when some differing species are > mated, there is a finite but very small probability of offspring surviving > at least to birth. Eventually, mutation can drive the probability of viable > offspring to zero for all practical purposes. The gradual nature of > speciation is thus driven by probabilites rather than absolutes. This makes > the chicken and egg problem difficult, because it is difficult to define the > first chicken, or to distinguish it from its parents. > > > >> >> IOW you are suggesting that small populations speciate as a whole, rather >> than >> individuals. > > Yes > >> This would appear to be possible with regard to characteristics >> that do not influence the ability to produce fertile offspring, however >> that >> then is no longer the definition of a new species. > > It seems to me unlikely that single mutations produce new species, and that > the process normally must take a long time, multiple mutations, and isolated > populations, geographically or otherwise. The process of speciation might > be highly influenced by environmental factors however, and such a speciation > even could be rapid. A sudden change of environment could bring on the > immediate and simultanenous *expression* of many genes at once via epigentic > influence, and this expression could simultaneously impact large portions of > a population, as well as their genetic compatibility. Alternatively, large > segments of DNA could be sown throughout a population via viral infection, > creating a group of individuals incompatible with the prior population, but > compatible with each other. Evolution may have multiple pathways available. > > >> >> The only natural solution I can think of is that a new species is created >> when a >> genetic mutation occurs in all the offspring of a single individual, and >> those >> offspring mate with one another. >> >> The only alternatives I can think of are "unnatural", i.e. genetic >> manipulation, >> or the same mutation occurring at the same time in different individuals, >> that >> then produce offspring that can mate. The latter would however appear to >> be far >> less likely than mating between offspring from the same parent. >> Regards, >> >> Robin van Spaandonk >> >> http://rvanspaa.freehostia.com/Project.html >> > > Best regards, > > Horace Heffner > http://www.mtaonline.net/~hheffner/ > > > > >
