Limits of Kinds (was Fall of evolved man)

Karen G. Jensen (
Thu, 6 Nov 1997 22:50:09 -0600

Hi Glenn,

On Thu, 06 Nov 1997 05:39:09 -0600 you wrote

>However, the morphological change between a chihuahua and St.Bernard is
>astounding so where is the limit? What evidence is there of a limit to
>change in this example?

The limits show up when you get to the extremes of the available genetic
capabailty of the kind. For example, in dog breeding -- say breeding
collies with longer and longer noses, there comes a point where longer
isn't better, because circulation problems etc. develop, and the dog has
trouble breathing. Beyond that, longer is not only not better, it is not

Dog variation is indeed astounding, but not unlimited. You cannot get a
dog the size of a fly, for example (for many reasons, structural and
otherwise), or the shape of a stingray, etc. A dog has dog structures for
dog purposes...operating within "dog parameters" (!)

But, again,
>>There has been a lot of speciation, I believe to the family level in many
>>plant kinds, and some animals. Things have had to adapt a lot as the
>>environments have changed. This doesn't negate the concept of kinds. It
>>shows how much versitility has been given to living organisms. But there
>>are genetic limits, as plant and animal breeders well know.

An interesting sideline of this, I have heard that the limits are reached
within about four generations of intensive breeding. It surprizes me that
it would be so few generations. Does anyone have documentation on this?