Re: Speciation - how do you know?

Nick Maclaren (
7 Sep 1996 11:26:11 GMT

In article <>,
Stephen Barnard <> wrote:
>Tim Edwards and/or Marghie Parsons wrote:
>> In paleoanthropology, how do researchers determine that one creature
>> is not the same species as another? Am I correct in my understanding
>> that the question is still open vis-a-vis modern humans and
>> Neanderthals? Is it pretty much accepted that Homo Erectus was a
>> separate species?
>The short answer is that, with respect to extinct species, you don't
>really know. Paleontologists make educated guesses based on
>morphological features. The most commonly accepted definition of
>species is a population of organisms capable of producing fertile
>offspring. This criterion will never be established from mere bones,
>but pretty good judgements can be made.

It is actually worse than that. Species were originally defined by
taxonomists as merely one level in a hierarchy (and not necessarily
the most important). Darwin explained how they came about, but other
people have elevated speciation into the status of a religious dogma
(primarily in vertebrate zoology). There are good species that can
produce fertile offspring (lions and tigers, for example), but don't
do so under 'natural' conditions. And so on.

When you bring the time dimension into it, things become much more
confused. For example, you would agree that mammals give birth to
infants of their own species? Well, we have continuous descent from
a proto-human that was unquestionably not of our species, if we go
back far enough. At some point, one species will have changed into
another, between generations :-)

So, defining species has to be subject to judgement, and there will
always be cases that could be described as somewhere between two
species, or as extreme members of one or the other.

Of course, not being a paleoanthropologist, I cannot possibly guess
where the boundaries lie, but the above may help to clarify the
confusion (sic).

Nick Maclaren,
University of Cambridge Computer Laboratory,
New Museums Site, Pembroke Street, Cambridge CB2 3QG, England.
Tel.: +44 1223 334761 Fax: +44 1223 334679