Repetitions within a given genealogical tree provides some information about
the degree of consanguineity of a population. They can be analyzed with
techniques usually employed in statistical physics when dealing with fixed
point transformations. In particular we show that the tree features strongly
depend on the fractions of males and females in the population, and also on the
offspring probability distribution. We check different possibilities, some of
them relevant to human groups, and compare them with simulations.Comment: 2 eps figs, Fig.2 changed to meet cond-mat size criteri
