Our aims were to demonstrate that natural selection is operating
on contemporary humans, predict future evolutionary change for
specific traits with medical significance, and show that for some
traits we can make short-term predictions about our future evo-
lution. To do so, we measured the strength of selection, estimated
genetic variation and covariation, and predicted the response to
selection for women in the Framingham Heart Study, a project of
the National Heart, Lung, and Blood Institute and Boston Univer-
sity that began in 1948. We found that natural selection is acting
to cause slow, gradual evolutionary change. The descendants of
these women are predicted to be on average slightly shorter and
stouter, to have lower total cholesterol levels and systolic blood
pressure, to have their first child earlier, and to reach menopause
later than they would in the absence of evolution. Selection is
tending to lengthen the reproductive period at both ends. To
better understand and predict such changes, the design of planned
large, long-term, multicohort studies should include input from
evolutionary biologists.
A
re contemporary humans experiencing natural selection
and evolving in response to it? The answer to that question
depends on whom one asks. A long tradition in the medical
community (1) holds that natural selection does not operate on
contemporary human populations because medicine keeps
‘‘alive many who otherwise would have perished’’ (2). No
evolutionary biologist would now agree with that claim, for
natural selection works through differential reproductive success
rather than simple differential survival, and individuals in con-
temporary human populations vary in lifetime reproductive
success (LRS). Selection operates on any trait that varies and is
correlated with LRS, and traits respond to selection with change
across generations if they vary genetically. But what traits is
selection operating on? Do they include the traits treated by
physicians? Previous work (e.g., ref. 3) has shown that human life
history traits, most significantly age at first reproduction, are
currently under selection, but evidence for selection operating
on traits of medical importance is scarce. Here, we report
estimates of natural selection, and the potential genetic response
to selection, in the women of the first two generations of the
Framingham Heart Study (FHS) population. The traits we
analyzed include traits of medical significance: total cholesterol
(TC), systolic blood pressure (SBP), diastolic blood pressure
(DBP), and blood glucose (GLU). We had three general aims:
first, to correct the still widespread misconception that natural
selection is not operating on contemporary humans; second, to
make quantitative predictions about future evolutionary change
for specific traits with medical significance; and third, to register
firmly a point of general cultural interest that follows directly
from our first two aims: We are still evolving, and for some traits
we can make short-term predictions about our future evolution.
