On May 24, 2009, at 2:07 PM, [email protected] 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/
