Re: Gracile and Robust Hominids on Java

Michael Daunt (
25 Dec 1996 00:15:28 GMT

James Howard <> wrote in article
| I suggest increases in testosterone drive human evolution. Human males
| females produce more testosterone than male and female chimpanzees,
| respectively. While I think the very large increase in brain size of H.
| is due to effects resulting from latitudinal migrations, small increases
| testosterone over time could cause small increases in brain capacity.
| effect may be seen today as the "Flynn Effect." In a "position locked"
| situation, such as Java, it is very possible that increases in skull mass
| cranial volume could occur in situ. That is, in a "breed and feed" area,
| lower testosterone hominids could not flee higher testosterone hominids,
| testosterone will continue to increase. This could account for the
larger brain
| capacity of the "H. erectus" specimens found in Java, compared to H.
| elsewhere. It is also part of my of theory that increased testosterone
| increases vulnerability to infections. Therefore, hominids of lower
| testosterone, i.e., more gracile hominids, could arise out of the
so-called H.
| erectus on Java. This could account for robust and gracile hominids, H.
| and H. erectus, on Java. The very large bodied, large brained,
| could arise by the same mechanism in the "position locked" environment of
| age Europe.
| James Howard

If I understand you correctly, you are saying that increased testosterone
levels are responsible for human evolution, and that these levels continue
to increase.

In my opinion, the Flynn Effect and human evolution are not linked. The
Flynn Effect shows increasing scores on intelligence tests over the past
century or so. To my knowledge, there is absolutely no link between these
test scores and testosterone levels. In addition, the timeframe is much
too short to draw any conclusions about the evolution of our species.

To bolster your theory, you will need some hard data. For example, can you
show that testosterone levels have risen in the general population over the
last hundred years? You will also need a much stronger theoretical
framework showing how increasing testosterone can both increase
vulnerability to disease, yet still give an early hominid some evolutionary
advantage over its rivals.

I have never come across any reference to a link between testosterone
levels and intelligence in humans. I am far from being an expert in this
field, but I doubt that such a link can be demonstrated. You need to build
your theory on the facts, not build a theory and then try to convince
others through logical argument alone.

Michael Daunt