July 25, 1960

Miss Abigall Van Buren
The San Francisco Chrontcle
San Francisco, California

Qear Miss Van Buren:

Your letter of July 26 was given to me by Professor J. Lederberg.
You ask whether the likelihood for normal offspring In consar:gulneous
marriages is Increased when there Is no hereditary abnormality known
in the common families. No quantitative answer te this question Is
still available, but the increase in favorable chences which can be
wotained by tiie knowledge you mentioned is likely to be so small
that 1 would not recommend using It to counterbalance other arguments
against consanguineous marriage. Most hereditary abnormalities
tend to remain concealed and the rarer ones are often revealed
primarily tn the progeny of such matings.

+

Yours sincerely,

tL. L. Cavalli-Sforza
Visiting Professor
of Genetics