hall at deleteme.ns.utk.edu
Mon Sep 21 19:24:43 EDT 1998
John Grehan wrote:
> I don't understand what's subtle about orthogenesis. Could you clarify please?
OK, first you need to explain what orthogenesis is, because I only got a
vague sense of it from your previous post.
> Perhaps I would agree with you on this, although it does not change
Was there more to this sentence? I think that some of your sentences
are being truncated by the software that you post with.
> A new mutation arises (chance or whatever) in an individual. This
> individual mates
> with another. The offspring all have the mutation. These offspring mate
> with other
> individuals without the mutation. All individuals of this generation also
> now have
> the mutation. The mutation gradually spreads through the population without any
> differentiatl success in the fecundity of those individuals with the
> mutation, but all
> offspring will have that mutation.
OK, first of all, except in clonal organisms, individuals do not pass on
all of their genes to all of their offspring. Only if the mutation
simultaneously occurs on both chromosomes (highly improbable) will it be
passed on to all offspring. More likely, half of its offspring will get
the novel gene.
Even if all of the offspring of that first mating get the mutant gene,
they are heterozygotes, so 1/4 of their offspring will have the mutant
gene on both chromosomes, 1/2 will be heterozygotes, and 1/4 will not
have the mutant gene at all.
In the more likely case of half the F1's having the mutation and
assuming random mating, you get 1/8 of the progeny being homozygous
mutants, 1/4 being carriers, and 5/8 not having the mutant gene at all.
Your scenario only includes offspring of the one initial mating, and
naturally there would be many more matings among individuals not bearing
the mutation in a real population. On the population level, then, the
presence of the mutation would be much more dilute, even after a few
generations of 100% mutant survival.
Still, though, I understand what you are describing. It is the neutral
theory of Kimura, which posits that many mutations have little effect on
their bearer's fitness, and the process of drift, whereby allele ratios
change stochastically and not because of selection. This stuff is
standard evolutionary biology and not some major alternate theory,
though your careless math makes it seem more powerful than it is.
Surely you wouldn't claim that the possession of wings, even weak,
barely functional wings is a neutral mutation offering no improvement in
survival, dispersal, or mate acquisition, would you?
> acknowledge we may disagree. I envisage the
> possiblity that wings evolved through a series of mutuations arising and
> without increasing the fitness of those individuals with the mutations
> (series - assuming that
> wings in their modern form did not arise in a single step).
If there were no fitness differential, then we should still be seeing
populations with some fractional portion bearing wings and some majority
retaining the ancestral wingless state. There ain't many insects whose
populations look like that.
So how did we end up with millions of insect species whose populations
are uniformly winged? I suppose that they are not species at all, but
merely mutants fragments of the Insectan ultra-population? or the
Arthopodal ultrapopulation, or the Invertebrate ultrapopulation? Do you
acknowledge a species concept? This evolution-without-selection concept
seems quite problematical to me. Where are all the wingless insects?
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