>I find this discussion on sub species quite confusing.
Steve, keep in mind that taxonomy is a human construct, based upon
generally agreed-upon, but perhaps biologically arbitrary distinctions.
Life on this planet has evolved to adapt and survive, rather than to fit
neatly into any particular classification. New "species" are continually
differentiating themselves from existing "species."
For example, the caribou species breeding population got split when the
ocean rose to isolate it into two geographically-separated populations, and
then humans applied selective pressure to the populations called reindeer.
In general, a "species" is defined as "a group of living organisms
consisting of similar individuals capable of exchanging genes or
interbreeding."
The key definers are having a "breeding population," and appearing
"similar." So in the case of caribou, the European and American
populations are still capable of producing fertile offspring if they are
inter-bred (which would require human transport), and appear "similar."
But given time, they may evolve into clearly different species.
And then there are wolves and coyotes, which do not appear to be "similar,"
but can and do interbreed.
A number of species of waterfowl appear similar morphologically, but don't
normally interbreed, due to different mating behaviors.
My point is that nature is messy, with species continually "trying out,"
and adapting to different niches. If successful, a new breeding population
may occur, and then over time, differentiate morphologically and eventually
become so genetically different that they are unable to produce fertile
offspring if bred back to the parental species.
To better understand the sometimes-messy process of speciation, take a look
at an interesting salamander found in my area (I was holding one in my hand
last week)--click through all the pages at
https://evolution.berkeley.edu/evolibrary/article/_0_0/devitt_01
--
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com
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