Re: How does a new species emerge?

From: Philip Deitiker (Donevenask_at_worlnet.att.net)
Date: 08/26/04 

Date: Thu, 26 Aug 2004 13:38:41 GMT

johnSPAM@wilkins.id.au (John Wilkins) says in
news:1gj46d1.cysuwz1v45l1cN%johnSPAM@wilkins.id.au:

> Philip Deitiker <Donevenask@worlnet.att.net> wrote:
>
>> johnSPAM@wilkins.id.au (John Wilkins) says in
>> news:1gj2t5r.tll1ke1xd8d1qN%johnSPAM@wilkins.id.au:
>>
>> > Philip Deitiker <Nopdeitik@att.net.Spam> wrote:
>> >
>> >> 5. Sh!t happens speciation. This is when after a long
>> >> period of regional spreading and failure to form
>> >> isolates that rate of barrier formation exceeds the
>> >> rate at which genes flow across the population,
>> >> selection is for speciation within certain groups. The
>> >> basic assumption here is that the 'barrier' genes drift
>> >> across the population at a slow rate, that selective
>> >> genes can cross the barrier until the barrier genes
>> >> become selective on their own, and the barrier seals
>> >> up.
>> >
>> > I didn't forget it - I don't even understand it. What
>> > are selective genes and barrier genes? What is barrier
>> > formation? How is this significantly different from
>> > (depending on conditions) allopatric or sympatric
>> > speciation?
>>
>> Sympatric involves separation into 'niche' maximization or
>> stratification.
>>
>> Allopatric involves a separation that precedes speciation
>>
>> Whereas you could say Semiallopatric which would imply
>> that there is not complete separation, but that mate
>> selection is not random and maybe focused for cultural
>> reasons to within the group and gene flow is slow relative
>> to the evolution of traits that might alter fertility or
>> sexually viable crossprogeny in pairwise sampling.
>>
>> Semiallopatric is too long, and '*** happens' frustrates
>> people whose patron saint is a thesaurus; :^).
>
> Are you referring to Mayr's "dichopatric" speciation here,
> or something like Wu's "speciation genes" hypothesis? In
> any case I fail to see what you mean by selective genes and
> barrier genes.

The barrier gene meaning that no extrinsic barrier separates two
species, the barrier is intrinsic meaning they could potentially
mate, intermix by choice [key word is choice], but generally
fail to intermix and when they do mate fail to produce
crossprogeny that have good reproductive fitness.

> Can you elaborate, as I still don't know
> what you mean?

We define species per say as groupable organisms that for
example if we could plot several distinquishing traits on a
multicomponent plot with all other species, that these species
would form an 'object' in which the cloud created by the
scatterplot should not overlap with other scatterplots. This may
or may not be a formal species and the separation may only be
due to isolation. Whereas a formal species would, as I would
define it, that you take several samples of opposite sexed
members and cross them, within the species the opposite sexed
members while produce crossprogeny and the between an opposing
group they will not produce viable crossprogeny.
  The construct on this argument is that the breeding has to be
of some free will. IOW keeping two animals in a zoo and
depriving both of opposite sexed individuals of their own
species for a long period, or using artificial insemination or
other technological strategies would violate the natural limits
of a formal species, IOW they would overcome the genetic
predisposed limitations for crossbreeding that might exist if 2
individuals came into contact with each other in the wild.
  Therefore at the formal species level geographic isolation is
only a formative variable, it is not 'the barrier' and from a
species definition point of view the nodality of a
[sub]populations genetic traits are only potential indicators of
a formal species, the actual limits to crossfertility may not be
measurable in a 'feild biologist's' repertoire of
identification, and a biologist cannot always test the formal
constraints.
  As a result the definition of a species may not be in phase
with the actual limitations on crossbreeding. The process of
speciation which might resolve this is not visible in most
context because of time frames. However there are examples of
rather closely related populations that failed to produce
fertile crossprogeny that are successful when challenged. While
it may be true that one or the either group has gone through an
isolative period, the gross morphological differences are
inadequate to define cross-infertility, the [end resulting]
cross-infertility has occurred at the submorphological or
micromorphological level. This I think is well established now
and I do not need to defend this, in essense morphological
differences within a genera is often not the best predictive
determinant of 'formal' species boundary. So what is the best
predictor, or should I say what can be added to the list of
predictors that would improve its ability to predict without
actually testing.
  The resolution of the problem in terms of the process, the
process does not neccesarily require isolation but does need
spread and numbers. The problem is between two or three aspects.

1. The prospect of breeding with an individual at great distance
(Maintaining the ability to breed with an individual at great
distance, negative selection for such speciating genes

2. Genetic drift

[optionaly] 3. Positive selection for traits that

If mutation and genetic drift are faster than the rate at which
gene flow occurs across the total population then specific
traits which can lead to speciating might occur even with no
strict barriers in place.
  For instance lets say you have a population of animals in
North and South America. NA Animals are free to travel to SA and
vice versa. However free to travel animals typically never
travel more than 10 miles from their place of birth to breed,
and when they travel they tend to interbreed into larger groups
versus shorter distances to interbreed in smaller groups. Over
time the north american population will evolve, only members
that exist between the two populations will continue to
hybridize and at the extremes of all populations new formal
speciating elements (FSE)are evolving; however incompatible
traits that form in the north, for example, because of the rate
of gene flow, the predominant trait would negatively select the
more recent traits. There would then develope an incompatibility
boundary between north and south america. The boundary would not
be 'formal' in the sense it would only initially limit
infertility because the intermediate group would have both
SA FSE, NO FSE and NA FSE. SA FSE could cross with NO FSE and NA
FSE could cross with NO FSE. This however would only be
negatively selective at the north end of the SA population
whereas the rest of the SA population would eventually replace
the NO FSE state with the SA FSE, and crossfertility could then
only occur with the 'core' state. THe same would be said of the
NA population. Eventually the gene flow from essentially
speciated populations would push the intermixing zone into a
smaller and smaller region. At the same time the hybridization
zone at the center would have reduced rates of reproduction, and
decreased fitness because of gene flow and the incompatibilities
it creates. So at the same time the north or south population
could burst into the intermediate zone via a wholescale
migration (rule violated because the number of competitors
reduced) adsorbe some members and essentially create a broad
boundary between 2 species.

>From a human point of view I have created the following optional
scenario (3). The evolution of the human mind is tied to human
cultural evolution, the selection of mental capability is at the
level of culture, and it acts not only on the individual but the
group. One of my predictions, based on the study of HLA, is the
behavioral variation in humans is under a heterozygous selection
at the constraint selection by other group members (positive)
and thus unfavored behaviors are negatively selected. Like HLA
this primarily falls under mate selection stategies. This
strategy has been maintained in human evolution to provide
complimentary abilities in group members such that group members
can specialize and therefore the group itself becomes like an
individual, because no one individual can possess all traits and
accomplish all tasks for the group. During the course of human
evolution there has been selection by the groups for new traits
that add new cultural elements to the group, the group percieves
the addition of new elements and then positively selects the
individual who provides these elements by the provisions of
mates or mating opportunities. The added cultural elements are
then used for competitive expansion of the group. Therefore
there is a connection between the appearance of traits and
culture and thus the competitiveness of a group. However culture
could ebb and flow between groups, the inventer of a new culture
need not be present when it is copied, nor his genes. Therefore
the culture might become proprietary to the group, and the
genese that allow this (since not all members of the group might
possess all genes at the time) also 'desirously' proprietary.
Groups themselves may not be aware of this, but selection for
groups that resisted intermixing after acquiring new
predisposing genes would maintain a greater ability to
selectively expand compared to groups that mix out traits and
culture, and failure to interbreed may reinforce the culture of
exclusion and result in a failure for culture to flow via
channels of gene flow typical between groups.

In such a scenario the rise of culture producing traits at rapid
pace, such as during the pliestocence, could result in the
positive selection of intrinsic 'barriers' that are completely
out of synch with any geographic barriers and potentially could
result in more rapid speciation under circumstances where it
would have otherwise required certain environmental change or
disruption in situ. Whereas this is also not a situation where
teh groups overlap, because overlapping groups would facilitate
cultural motion, once a group goes into 'proprietary' mode they
would neccesarily expand to remove interlaced groups from their
territories until they reached a geographic position in which
the competing groups had greater temporary regional advantage
over them.

  I see this as what happened in africa, as the best explanation
for the developement of the human species. And at any given time
any of these groups (probably with varying capability of
intermixing over long ranges, some with more 'core' like
intermediate capability, some more self-isolative). Geography of
course helps this, extreme arid adaptability or extreme wetlands
adaptability could, genetically, both have created that 'last'
pocket from which humans emerged. But neither of these I think
is key, because it appears that an extension of the african
population in the northeastern eurasia did the same thing. The
fact of the matter is that protohumans may have been deligated
as a shrinking pod within africa of another 'proprietary' group
that then gets the tables flipped on it as protohumans get the
next 'trait' and the human population bounces out of 'generic'
competitive constraits and then displaces the group that was
going to displace it and it appears that no further development
elsewhere in the world could stop this.
  If this scenario is a valid scenario then my prediction is
that if competitive isolation and selective speciation(3) is the
cause, then the selective genes will be most intense at the
boundary and may fade in intensity in contact with other groups
elsewhere. This would mean that while humans could not mate with
other proximal groups potentially they could mate with more
distal groups. The evidence at the moment favors the potential
intermixing with populations in east asia, but not in
supersaharan africa(Levantine or Morrocan) or NW Eurasia
(Neandertals).
  It may be true that this is just semantical and that one could
apply sympatric speciation to this example; however I don't
think it is fair to call it sympatric if the inevitable
consequences on interregional mosaic formation is the
elimination of one group for another, that two groups cannot
coexist in the stable state. This is not true for sympatric
species, and if one or either group is eliminated it is not due
neccesearily to competition between the 2 derivatives, which
would have to be the case in the example above. So I don't think
you can call it sympatric speciation without changing the
definition. 

-- 
Philip
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