Yes, on this point there is no disagreement. It is an aspect of
allopatric speciation. Whether the variant dogs would be classed
as separate species is still doubtful: they all have 78
chromosomes and are very close to their grey wolf ancestor. Dogs
are morphologically very variable but genetically very similar
(as is pointed out by Nigel Crompton in his study of the family
Canidae in the book I mentioned in my previous correspondence:
*Typen des Lebens*).
Glen wrote:
"The horses make an even more interesting situation. The modern
horse has 64 chromosomes. Przewalski's horse has 66... What has
happened is that one of the horse chromosomes has broken giving
Przewalski an extra pair of chromosomes. Amazingly, Przewalski's
horse and the modern horse can produce fertile offspring".
Agreed - all very interesting. But similar surprising
hybridisation data is found for the Canidae: Canis familiaris (78
chromosomes) will cross with Cerocyon thous (74) and Vulpes
vulpes (36 chromosomes), etc.
Glen wrote:
"Other horse-like animals show different chromosome numbers also.
The Persian onagers can have 55 or 56 chromosomes, kiangs can
have 55 or 56. Kulans have 54 or 55. So we can see cellular
morphology changes which lead to reproductive isolation and
morphological change between these species. Where is the
evidence of a limit?"
Interspecific hybrids have been observed between all six species
of the horse family (Equidae). The conclusion of Heike Stein-
Cadenbach in *Typen des Lebens* is that "This basic type is
deeply separated from other perissodactyl groups". The general
point I am concerned with is that here is objective data (from
hybridisation studies) which can be used to identify a bounded
group: evidence for unlimited variation is sparse.
Glen wrote:
"How can I predict exactly what the extent of morphological
change is in these equines?"
I don't think anyone is in a position to make predictions.
However, the Basic Type analyses are throwing up many ideas on
chromosome evolution and sources of variability which have been
missed by evolutionary biologists - because they are working
within a different paradigm.
Glen wrote, referring to YECs and PCs:
"Unfortunately, not all do believe in speciation".
I recognise that there are many creationist voices asserting
things which I regard as indefensible.
Glen wrote:
"Why should they [neoDarwinians] have to be the only ones to
prove their point? Why are anti-evolutionists exempt from having
to justify their position? What you are asking is the
impossible. Since logically it is very difficult to prove a
negative (it can't be done), it seems that it would be more
fruitful for the anti-evolutionist to prove the positive i.e.
that there is a limit to variation. No one can prove that there
is NO limit because that violates the laws of logic. But you as
a believer in limits, should be able to prove the extent of
variation".
In one sense, you are quite right - anyone wanting to say
something positively in science should be expected to support it
with evidence. However, my comments were made in the tradition
of Phil Johnson - who is seeking to open up the issues for
debate. There are major assumptions in neoDarwinism which have
never been justified scientifically. Unlimited variation is one
of them.
Gordon Simons wrote:
"It seems to me that the real difficulty in the present
discussion has to do with the imprecision of the use of the word
"limitation". How limited are morphological changes? Until this
is clearly stated, there can be no clearly stated refutation".
I am sympathetic with the comment. We lack the tools to describe
biological variability. How do we recognise limits? Stein-
Cadenbach says that one family of animals is "deeply separated"
from others - but can this be quantified? I would suggest that
we are struggling within an paradigm which has been defined and
developed by neoDarwinians: because they have not seen this as
an area of research interest, they have not developed tools to
permit the serious study of limits to variation. This is a
challenge to biologists who do recognise natural groupings in
animals and plants: new tools need to be developed to quantify
the observations.
Best wishes,
*** From David J. Tyler, CDT Department, Hollings Faculty,
Manchester Metropolitan University, UK.
Telephone: 0161-247-2636 ***