[extropy-chat] Hybrids

[Robert J. Bradbury]

On Thu, 29 Jan 2004, David Lubkin wrote:

> No one responded to the question I posed a couple weeks ago, so I'll ask
> again. It was asked in a reply to a religious thread, so many people may
> have missed it.

Perhaps.  I tend not to follow threads that would appear to have
a high debate-to-data content.

> >How is it that a horse and a donkey -- different species, with different
> >numbers of chromosomes -- can produce offspring?  What are the limits of
> >cross-species mating, besides incompatible hardware, e.g., horse and
> >gerbil?  Given species x, y and gestational periods g(x) and g(y),
> >respectively, what will the gestational period of an x carrying an x/y
> >hybrid be?

The gestational period is probably largely dependent on the hardware in
the mother.  But to the extent that the offspring signal "ready to go"
there will be some interaction.  [Note -- I am not up-to-speed on the
extent to which these signals vary across species.]

Chromosome variations are not too difficult to work around.  To the best
of my knowledge there are 3, perhaps 4, known situations where humans
can be born with an extra chromosome (trisomy).  Most of these individuals
suffer early deaths, though trisomy 23 (Down's syndrome) can have a
relatively long life.  The chances for viability go up with the increase in
chromosome number (higher chromosome #'s are smaller and have fewer genes
and therefore are less likely to cause gene dosage problems).

There is amazing amount of cross-species genetic matching -- you can take
the human genome and the mouse or rat genome and match those segments
from one genome precisely onto segments from the other species.  Whether
or not mating gives you viable offspring depends in large part on what
sequences may have been duplicated or deleted during the production of
the gametes.  Rarely will you get combinations that don't have problems --
but that is how most if not all all speciation seems to take place
(losing or gaining genes and at a higher level losing or gaining chromsomes).

> Just as I want some people living off-Earth in an environment that can be
> viably self-sufficient with primitive technology, I would prefer that
> humans not fracture into reproductively incompatible successor species.

If we have the ability to live off-Earth I *really* doubt we would not have
the ability to construct de-novo genomes.  (The business plan for Robiobotics
which leads to de-novo genomes is *much* closer to reality than Mars colonization).

Now whether or not one wants to preserve the ability for normo-homo-mating
would be an interesting question.  One has to argue that this has some
survival benefit in the situation that technology (and even the knowledge
of such technology) is somehow driven back to the dark ages or earlier.

I'm still waiting for someone to argue that an "Extinction Level Event"
(asteroids, comets, nuclear war, etc.) is going to eliminate nuclear
submarines and all of the knowledge/technology they embody.

Robert