The researchers found a "significant correlation" between males who babysat and the presence of germline chimerism: These males were found to rear chimeric infants more often than nonchimeric ones.
"Although the exact mechanisms of sociobiological change associated with chimerism have not been fully explored, we show here that chimerism alters relatedness between twins and may alter the perceived relatedness between family members, thus influencing the allocation of parental care," the study says.
Study author Ross said the findings could also cause researchers "to redefine what it means to be an individual in this species."
"This study is exciting," added David Haig, an evolutionary biologist at Harvard University, "because, in a genetic sense, twin marmosets could be cousins instead of siblings."
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