Christine, John Galt knows the following article will interest you
severely. You should know, too, John wears a size 22 triple A shoe.
Digital Penis
The penis may have more in common with other stubby projections--fingers
and toes--than most of us might have guessed. Researchers have discovered
that the same genes that direct a mammalian embryo to sprout digits also
tell male embryos to make a penis. The findings, reported in today's
Nature, suggest that the penis, fingers, and toes may have evolved under
control of the same primordial genes.
The first clue that digits and penises might be birds of a feather came in
1991, when a team led by developmental biologist Denis Duboule of the
University of Geneva and Pierre Chambon of the Institute for Genetics and
Molecular and Cellular Biology in Strasbourg, France, found that some mice
with a mutated gene, called hoxd13, had abnormally small digits and
malformed penises. The gene belongs to a family of so-called HOX genes,
which are active in controlling development of body segments and appendages
in a wide range of organisms. Then last February, a team led by Jeffrey
Innis of the University of Michigan, Ann Arbor, showed that people with a
hereditary disease called "hand-foot-genital syndrome" have a mutation in a
related human gene, HOXA13. This rare disease leads to short thumbs and big
toes and sometimes a urethra shifted to the base of the penis.
Those findings prompted the two teams to work together to breed mice
lacking four genes: three hoxd genes and a mouse version of hoxa-13, which
together are known to direct the development of limb ends. The embryos
survived long enough to have distinct anatomical defects, including missing
lower limbs and digits--and the absence of the entire lower urinary tract
and penis. This suggested to the team that digits and penises might have
emerged from the innovative use of the same genes: HOX genes. "Perhaps the
origin of the penis correlates to the introduction or improvement of the
digits," says Duboule.
The finding "strengthens the genetic connection between genitalia and limbs
and feet," says cell biologist Bjorn Olsen of Harvard Medical School in
Boston. But others are skeptical about whether this genetic connection
extends widely in the animal kingdom. Axel Meyer, an evolutionary biologist
at the University of Konstanz in Germany, says that sharks, fish, and other
aquatic creatures have penislike appendages that evolved from finlike
structures that had nothing to do with limbs.
Science, 6 November 1997 08:00 PM |
