The golden lion tamarin, a one-pound primate that lives in Brazil, is a stunningly monogamous creature. A male will typically pair with a female and they will stay close for the rest of their lives, mating only with each other and then working together to care for their young.
In mammal species, there are 9 percent of them living in a deeply monogamous way. Biologists get puzzled that a seemingly better evolutionary strategy for male mammals would be to looking for other females to mate.
Dr. Lukas, co-author of a paper in the journal Science with Tim Clutton-Brock of Cambridge, looked at 2,545 species of mammals, tracing their mating evolution from their common ancestor some 170 million years ago. The scientists found that when females become hostile with one another and live further. One single male cannot prevent other females. Staying close to one female became a better strategy. Once males began doing so, they sometimes evolved to provide care to their offspring as well.
Dr. Opie and his colleagues examined 230 primate species, because monogamy is especially high in that group. They made a different hypothesis: the threat of infanticide drove the evolution of monogamy. In many species of mammals, makes will sometimes kill the young offspring of other males so that a male then gains the chance to have offspring of his own with her. Nursing females do not ovulate.