Re: Why are we still evolving? (from sci.bio.evolution)
James Howard (firstname.lastname@example.org)
Thu, 15 Aug 1996 14:23:59 GMT
A lot of response to this question at sci.bio.evolution involves
people getting taller. What they mean to say is that the "secular
trend" is ocurring and feel that this indicates that we are, indeed,
evolving. I agree this is a sign of current evolution in Homo
sapiens. A number of the respondents feel the secular trend is due to
increased nutrition. This is the usual explanation of the secular
The secular trend is an increase in height, weight, and earlier
puberty. Now, if it were food, we should see some differences in
blacks and whites. Many believe that blacks, on average, have less
access to proper nutrition than whites. However, evidence shows that
blacks arrive at puberty earlier and exhibit other characteristics
that indicate a more rapid development.
"Black youths are known to enter into puberty at a younger
chronological age than white youths." American Journal of the Diseases
of Children 1991; 145: 142
"When children of European ancestry (whites) and predominantly African
ancestry (blacks) living in the United States are matched for
socioeconomic status variables, such as mother's occupation and
education, it is found that black children are consistently advanced
over white children in the formation and emergence of the permanent
teeth, and advanced in radiological appearance of ossification centers
of the skeleton and epiphysial union. The precocity in dental and
skeletal development of black over white children can also be observed
during the prenatal period." Patterns of Human Growth, Barry Bogin,
Cambridge University Press, 1988, pages 108-109.
My work suggests that hominid evolution is driven by the increased
testosterone in humans. (Human males and females have more
testosterone than chimpanzee males and females respestively.) I think
higher testosterone causes the signs of the secular trend, and, over
time, higher testosterone individuals will produce more children than
lower testosterone individuals.
Black males produce significantly more testosterone than white males
(Journal of the National Cancer Institute 1986; 76: 45). I suggest
this is why blacks enter puberty earlier than whites. It also is
directly involved in increased births among blacks compared to whites.
"The rate of teenage births is especially high in the black
population. An international comparison around 1980 revealed that the
black U.S. teenage fertility rate was 2.3 times the white and 3.2
times the average of 30 advanced countries. The contrast is even
greater among the youngest teenagers; blacks under 18 years of age had
a rate in 1980 that was more than three times that of whites.
Nonetheless, even white teenage birthrates were 40% higher than the
average for other advanced countries." Science 1986; 234: 554
So, yes, human evolution, based on levels of testosterone, continues
to occur. It continues to occur, because human evolution is based on
the sexual advantage of higher testosterone.