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I guess all the sensible things on this convergence issue
have already aptly been said by Vincent and Joe, but I can't resist to add
one little comment.
> > <Dawkins discusses this dilemma in The Blind Watchmaker: "It is
> > vanishingly improbable that the same evolutionary pathway should
> > ever be followed twice.
> > And it would seem similarly improbable, for the same statistical
> > reasons, that two lines of evolution should converge on the same
> > endpoint from different starting points. It is all the more
> > striking... that numerous examples can be found in real nature,
> > in which independent lines of eovlution appear to have converged,
> > from very different starting points, on
> > what looks very like the same end-point.
As it stands it is somewhat confusing as the passage casts a little doubt on
natural selection, I have to agree this much with Ted.
He raises confusion in the second part (It is all the ...).
Nonetheless, no unsurmountable problems for the theory of natural selection
I agree, the probability of two species parellely traversing
(i.e. both going through the same genetic changes) the same path of
evolution is statistically non-existent. But the emergence of two
species that superficially resemble one-another is quite finite.
Compare, for instance, carcharadontosaurus with tyrannosaurus-rex.
The odds of the showing-up of two similar species is very small, nonetheless.
However, given the fact that the earth has known and still knows many
species, the expectation value, i.e. number of species-pairs * prob. of
similarity at any given time, might be quite large. Therefore, from
a brute-force statistical point of view, emergence of two similar species
(albeit from entirely different genera) is not a sheer impossibility
but a fair possibility. Nature has obeyed this statistical rule at
least to fair degree by presenting a sufficient number of cases.
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