Scientists Explore this Monogamy Trend

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No reason marriage is difficult!  Only 9% of mammal species are monogamous.  Only 17% of human cultures are "strictly monogamous" (whatever that means).  Besides, we humans are fairly new to the monogamy game: our ancestors made the shift to monogamy about 3.5 million years ago.

Why is this an evolutionary puzzle?  Because theoretically males could have more offspring by mating with many females.  Yet it appears that males who stick around are able to protect and feed their offspring, increasing the chances of their survival.