Re: How can behaviour or the environment change an organism's genetic makeup?

Dear Sophie:
           The idea that the environment or behaviour can change an
organism's genetic makeup (DNA) is an old and wrong idea.  Before
Charles Darwin, a Frenchman, Jean-Baptiste Lamarck proposed a theory
of the inheritance of acquired characteristics.  For instance, suppose
modern giraffes had short-necked ancestors.  According to Lamarck,
the stretching of the necks of these ancestors to reach leaves higher
in the tree canopy caused fluid to accumulate in their necks which
permanently  lengthened them. The longer necks were then passed on to
the next generation.
          Darwin proposed, to the contrary, that in the original
population of ancestral giraffes, some individuals had longer necks
than others.  Those individuals which had longer necks were better
able to survive droughts and famines and were, therefore, able to pass
their genes for long necks to the next generation.  The short-necked
individuals (along with their genes for short necks) went extinct.
Thus, over many generations the neck of the giraffe population on average
became
longer and longer (i.e., the frequency of the genes controlling long-
neckedness became more and more prevalent). Darwin's ideas have
become the cornerstone of all modern biology.
         Behaviour/environment cannot change an individual's genes.
One is stuck with the genes with which one is born  (although molecular
biology may change this in the next decade or century -- see gene
therapy).