# Mathematical Digest

### Short Summaries of Articles about Mathematics

in the Popular Press

"Kissing Cousins: The Numbers Show We're All One Big Happy Family," by AnaBerlin. *The Sciences,* September/October 1999, page 9.

This article discusses a newly developed mathematical model of geneaology.Most such models rely on the fact that, counting n generations back, eachperson has 2^{n} ancestors. The new model takes into account the factthat, because human populations long ago were small, matings often took placebetween relatives. One therefore finds that two randomly chosen people alivetoday are likely to have a common ancestor---provided one looks sufficientlyfar back in their family trees. The new model, the article says, has"important applications for evolutionary biologists and populationgeneticists."

*--- Allyn Jackson*