Re: An alternative to ST and AAT

Paul Crowley (
Mon, 02 Dec 96 10:47:14 GMT

In article <01bbdfc5$277a52e0$LocalHost@dan-pc> "Rohinton Collins" writes:

> Oh dear, oh dear, oh dear. Intermediary stages? Do you think that the
> australopithecines, during their 2 million year existence, said:
> "Oh shit, we have to walk with this damned waddling gait because we're just
> an intermediary stage, just an evolutionary dead end. Such is our lot in
> life!"

Species can adopt what we, in retrospect, regard as an inter-
mediary stage for many millions of years. Think of almost any
taxa; e.g. early birds such as Achaeopteryx. A good parallel to
the Australopithecines would be the first quadrupeds on land.
They took many millions of years to "work out" that it would be
more efficient to have their legs closer to the centre line rather
than at the side. Did they say "Oh shit, we have to walk with this
damned waddling gait because . . . " ?

> The australopithecines were *obviously* terribly well
> adapted or they would not have existed for so long.

To say a species is "terribly well adapted" reveals a deep mis-
understanding - or a romantic tendency. Of what extant species
would you say it? Species adapt to their habitat. They are
good enough. They get by. It's no more than that.

> Evolution does not plan ahead.

Exactly. Many species could have a remarkable new adaptation just
around the corner, only they never find it. The Australopithecines
never "found" the efficient striding gait. Each individual had
other priorities during his/her life which determined how many
descendants he/she left behind.

> Intermediary species - those who are evolving rapidly from one
> stable species to another - are very unlikely to be preserved in the fossil
> record, since they exist for a relatively very short period of time.

As you said: evolution does not plan ahead. You cannot, except
in retrospect, say whether a species is, or is not, evolving into
something else. There is no reason why a species should not
achieve a "platform" which is both intermediary (when seen in
retrospect) and also successful and stable for an extended period.
Pick up any book on fossils to see numerous examples.