man-ape hybrid

Radford Neal radford at cs.toronto.edu
Sat Sep 16 13:43:10 EST 1995

> ... The human body is just way to complex to cross-bread with any other 
> organism...

I've been rather amazed at the depth of confusion on this issue, both
by posters who appear to be amateurs, and by those who claim
professional qualifications in biology.  (I am not in the latter
category, but I can think.)

The simple, and rather obvious, truth is:

    You can't tell whether a human-ape hybrid is possible without
    trying it.

The argument that humans and apes are different species, and by
definition different species can't interbreed, is obviously circular.
The slightly more reasonable argument that humans and apes can't
interbreed because we don't see any intermediate forms around ignores
two points: (a) whether humans and apes *can* interbreed is not the
same as whether they *do* interbreed - reproductive isolation might be
achieved solely by behavioural aversion, and (b) any occasional
intermediate forms might be highly selected against, even if they are
basically viable (even fertile), and hence we would be unlikely to see

Perhaps a professional might be able to argue that interbreeding is
impossible due to chromosonal incompatibility, but no one has
attempted this, and I doubt that present knowledge can conclusively
rule out interbreeding on this basis.  (Note that it is possible for
organisms with different chromosome numbers to produce viable, fertile
hybrids, as illustrated by the domesticated horse and the original
wild horse of Mongolia.)

The above argument that humans are "just too complex" seems to be
based on the completely false assumption that there is some enormous
gap in complexity between apes and humans (unless the intended claim
is that mammalian species generally are less likely to be able to
interbreed than "lower" species that have diverged equally long ago,
which would be a sensible hypothesis, albeit to my knowledge unsupported).

Contrary to some postings, the question is quite reasonable, and of
some philosophical interest.  Experiments to try to answer it would of
course be ethically controversial.  

   Radford Neal

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