How evolution works

Cathy Woodgold woodgold at seismo.emr.ca
Mon Jun 13 09:42:34 EST 1994


Sydney SHALL wrote:

>The "novel" idea that I would advance is that there is no natural
>selection in human populations since about the beginning of the 20th
>Century, because in general people are over-riding their biological
>ability to have many offspring by "social" decisions to limit the number
>of children.  In most parts of the world the number of children achieved
>is almost entirely a "social" not a "biological" decision.  

I agree that people usually choose how many children they will have.
However, I disagree that there is no natural selection!  Even if everyone
always chose to have exactly two children and those children always
survived to have offspring themselves, there would still be natural selection
for fast-swimming sperm and healthy egg cells, and for embryos that are
capable of developing into babies.  However, many people don't have exactly
two children.  For example, I know someone who had only one child, though
she would have liked more, because complications of her diabetes led her
to decide not to have any more children.  Of course, in a less technological
society such a diabetic would have died and had zero children;  but having
just one child instead of more is still natural selection against the genes,
if there are such, that predispose one to diabetes.  (More significantly,
perhaps, it's natural selection against the cultural practices, passed from
parents to children, that predispose one to diabetes.  Diabetes depends more
on nutrition than on genes.)  There is also natural selection for people
who love children and want to have lots of children.

By the way, humans have evolved, through natural selection, the qualities of
responsibility, intelligence, cooperation, etc. and many are now applying these
qualities to the survival of the planet by limiting the number of children
they have.  (Some choose to have zero children because "there are too many
people in the world", though they still want some people to have children to
continue the species;  others might stop, say, at five children, out of a sense
of responsibility, though they would have liked to have had eight.)

Cathy               TISSATAAFL






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