Re: Blog: The Scars of Evolution.

On Mar 23, 3:21 pm, Treus <treusd...@xxxxxxxxx> wrote:
hersheyh wrote:
On Mar 23, 12:20 am, Treus <treusd...@xxxxxxxxx> wrote:
hersheyh wrote:

Chimps have a genome. The human genome has a certain number of
differences from the chimp genome. The chimp genome has the same
number of differences from the human genome. Both populations are
alive and must have been alive ever since separation from a common
ancestor who had a genome as well; one that was neither human nor
chimp and differed from the human or chimp genome at about x/2 sites.
Clearly the *differences* that exist in the current population are not
lethal.

You seem to be claiming that, even though a species having *all* of
this set of differences survive quite well, that one having only
*some* of these sequence differences must be dead. Is that your
claim?

Basically.

And how could such a situation arise?

Incompatibility between the chimp and human parts (as it were), due to
reasons like those making proper chimps and humans mutually infertile,
in transitional morphologies connecting the species under the proposed
mechanism.

Such as? What gene sequence differences or phenotypic incompatibility
would produce a phenotypic incompatibility between chimp and human
parts so great that it would be lethal?

A subset of the genomic properties causing reproductive
incompatibility between the chimps and humans we see around us
nowadays.

But we *expect*, most of the time, two modern species to show
reproductive incompatibility. The fact that this is not *always* the
case and that intermediate stages of reproductive incompatibility
exists tells us that the present incompatibility need not extend all
the way to the common ancestor, even when that ancestor is in the
process (and it is ordinarily a process rather than an event) of
speciation.

Unless you can tell *which* of the many genomic differences that exist
between *modern* humans and *modern* chimps are involved in this vague
"subset of the genomic properties causing reproductive
incompatibility" that could NOT, in principle or in fact, have arisen
by a step-wise process. Again, you completely fail to recognize that
each and every genome *difference* that *accumulates* in the two
lineages after separation must either be by the selectively neutral
process or the selectively beneficial process.

We already know that in the
*hominid* lineage or in close branches off of it between the common
ancestor and humans, that early hominids developed the feature of
bipedal walking *before* there was a substantial change in brain
size. That is, there is no *mandatory requirement* that all the
features we regard as 'human' have to appear all at the same time or
death would result. We know that there have been changes in
morphology, but which of these changes would cause instant death when
they arose? I certainly don't see any feature of humans that requires
instant change or death.

The relevance of this is unclear, but I see the outlines of a
strawman.

How? I am pointing out that there is a stepwise process, among those
features that can be observed by looking at fossil evidence, involved
in *modifying* the features of the common ancestor to the *modern*
human. That would also be the case at the sequence level. After all,
the only mechanisms that can produce the *differences* between the
modern species requires either neutral fixation or beneficial
fixation.

Moreover, *most* of the *differences* between human and chimp genomes
are, indeed, due to selectively neutral fixation. These changes, by
the definition of selective neutrality, have no significant
deleterious (or beneficial) effect. The small number of *changes*
that *are* selected for would, again by the very definition of
'selected for', not be deleterious traits whose incompatibility leads
to death.

I will repeat: There are only two processes that produce *change* in
a genome. Both are observable processes. One is selectively neutral
fixation by a random walk. The other is selection for a favorable
trait.

So you have a model of chimps and humans which accounts for all the
essential differences between them according to replicable
evolutionary operations where the former is transformed to the later
while explicitly producing a viable zygote at every generation?

No. I have two mechanisms (the neutral or the selective mutation
fixation mechanisms) that are both *sufficient* to account for the
total amount of difference observed in modern human and modern chimp.
*Your* claim was that there is no known natural mechanism which is
*sufficient* to accomplish this. I chose to only look at the slower
of the two mechanisms because that one provides a specific expectation
whereas beneficial selection is a function of the degree of benefit.

Now, as I expected, you are trying to claim that there is some *other*
reason why these mechanisms cannot work involving some unspecified
sites that are somehow asserted to be responsible for the current fact
that humans and chimps are reproductively incompatible.

That means that *all* (well, there are a few mechanisms that
can drag along some mildly deleterious traits if the net effect is
still positive) the *differences* between human and chimp genomes are
differences that either have no selective effect or have a beneficial
effect in the lineage it occurs in. Your claim is that changes that
are, individually, selectively *neutral* cannot accumulate in a
lineage in a stepwise fashion and/or that changes that are,
individually, selectively *beneficial* cannot occur in a stepwise
fashion, but must appear in a single magical poof of smoke all at
once.

You have drifted considerably from anything I ever actually stated.

No. *You* are claiming that a stepwise process is impossible for some
reason. Initially, your claim was that the reason was that no known
natural mechanism was *sufficient* to produce the amount of
*difference* seen. Now you are claiming that because *modern* humans
and chimps cannot interbreed that there must be some gigantic magical
leap in "difference" that cannot be crossed even if the mechanisms I
propose can indeed account for the *amount* of difference observed.

As for the lineages becoming 'mutually infertile', there is nothing
that prevents reproductive isolation from being a gradual process.
Even today there are 'species' with subspecies groups that are
interfertile to greater or lesser extent. [Modern humans do not seem
to be among these species; humans show variation in phenotype, such as
color, size, shape of face, etc., without reproductive infertility
resulting.] There are even different species that *can* interbreed
fertilely but do not do so in nature because of geographical and/or
behavioral differences (ligers and tigons, anyone). These are
examples of *gradualism* in degree of reproductive isolation.
Reproductive isolation (speciation) often involves difference that
arise, by chance, *because* of isolation leading greater reproductive
incompatibilities.

There is no magic moment when, poof, a human is born from an ape.
Speciation (and there are exceptions like allopolyploidy) can be, and
often is, a gradual process that involves *populations* and not
individuals. This is just as silly as your claim that populations and
lineages go extinct because a single zygote can have a lethal mutation.

A lineage would not necessarily go extinct just because it is unable
to approach another species state via an evolutionary series in which
every generational element has a viable zygote. There is no apparent
reason why those things would go together. In fact, there is no
instance of the latter outcome happening at all outside the
storytelling paradigm of establishment McScience.

I don't think you know enough to tell. I say this because a lot of
what you are saying here is gobbledegook where you toss out terms
without really knowing what you are saying. What, exactly, would
prevent a lineage from moving from one species state to a different
one by a stepwise series of changes, if those changes can be
represented by ordinary mutations and if the changes represent either
selective neutrality or selective benefit?

.

Relevant Pages

  • Re: Blog: The Scars of Evolution.
    ... differences from the chimp genome. ... in transitional morphologies connecting the species under the proposed ... The other is selection for a favorable ...
    (talk.origins)
  • Re: "Random evolution"
    ... which we can measure evolution. ... By this measure it would be hard to argue that natural selection was the ... You have probably heard that the human and chimp genomes are roughly 98.5% ... are due to natural selection and how many are due to drift (i.e. ...
    (talk.origins)
  • Re: "Random evolution"
    ... which we can measure evolution. ... By this measure it would be hard to argue that natural selection was the ... You have probably heard that the human and chimp genomes are roughly 98.5% ... are due to natural selection and how many are due to drift (i.e. ...
    (talk.origins)
  • Re: The Theory of Evolution is a mathematically irrational belief
    ... sequence of the chimpanzee genome and comparison with the human genome. ... genome of ONE chimp individual and ONE human individual, ... and selection is nothing more than an optimization problem where the ... This will result in those sequences ...
    (talk.origins)
  • Re: Christians, sci-fi and Doctor Who
    ... It only shows your utter ignorance of the theory/ process of evolution. ... Mammals are incredibly complex, yet you expect a couple of hundred years ... A chimp can no more be made human than my ciggie can be made into a potato. ... that is far from natural selection. ...
    (rec.arts.drwho)