Re: AAT Theory

H. M. Hubey (
7 Oct 1995 14:18:44 -0400

chris brochu <> writes:

>2. There was an aquatic lineage within the rhinos (teleoceratids), but
>these have nothing to do with living taxa, who are descended from a long
>line of terrestrial animals. This is an important point, because we have
>direct evidence for furry rhinos in the Pleistocene. Clearly, if the fur
>was lost recently, it had nothing to do with water.

>3. For that matter, some extinct elephants were furry. Ever hear of the
>wooly mammoth?
>The point here is that hair loss may have occurred long after any
>supposed aquatic phase in proboscidean phylogeny.

>4. I think some of the arguments regarding heat loss and mass are
>missing the point. The important measure is *surface to volume ratio*,
>not just mass. Animals with a low surface to volume ratio lose heat more
>slowly than to animals with a high ratio.

The point is that the SST tries to take advantage of arguments like

It makes sense for humans to be at the extreme end of the
heat conduction spectrum; that is, our conductance must be maximum
for our size, and that requires that we be naked. If we want to
decrease the conductance we can just cover up with clothes. But
the conductance must be large enough to get rid of the heat
build-up during hot weather. But this doesn't explain the loss of
body fur during a hot-dry climate. It would be very cold at night.

The argument above is sort of borrowed from the arguments for the
rhino and elephant. It goes like this: the large animals like
elephant and rhino have to be naked to be able to expel as much
heat as possible since because they are so large, their mass scales
up faster than their surface area (skin) and thus they'd build
up more heat and couldn't expel it quickly enough with fur.
This is also used to explain the reasons as to why these animals
take to the water when it is hot; i.e. to expel heat better.

But the argument is not causal. If being large was going to cause
the animals to die of heat-stroke, then how did they get bigger?
They should have stayed small, instead of getting bigger and then
losing their fur to expel heat. Better yet, if it's still so hot
that they still need to go into the water to expel their excess
heat, then maybe they were doing this all along, and that
pretty much says that we could claim that they did have an
aquatic life style.

But now, this still doesn't explain why a furry little animal
about the size of a chimp lost its fur. Heat expulsion can't
be a factor at this size. If the temperature of the earth was
so hot that even animals of this size had to lose their fur,
then larger animals should have died out. So even if the idea
of losing fur is connected with heat expulsion, then it still
brings up the idea of an aquatic environment to further take
advantage of this process. It's hard to avoid.

PS. Still need an explanation of why humanoids lost fur during
the cold nights.


Regards, Mark