Female common lizards (Zootoca vivipara) get pickier with experience. Virgins will mate with almost any male. But the second time around, some favor males with more diverse genes, according to a study in this
month's issue of Behavioural Processes. This "trading up" helps moms gather a diversity of DNA, raising their chances of producing healthy
offspring. Most only birth young two or three times during their lives. So, to make good on the costs of pregnancy, female lizards need to choose the
father's genes wisely. At first, they may gamble on a male with less diverse genes to increase the chance of pregnancy. But after some of her eggs have
been fertilized, she can look around for better males. The researchers think the females may recognize genetic variation by sniffing out males' body
odor, a technique other species—including humans—use.
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