Eli5: how is it that so many species, including humans, have the same motherly instinct that suddenly appears after birth? Where does this come from?
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If a species has babies rarely, they only have a handful of opportunities to successfully spread their genes to the next generation. The ones who protect that opportunity after it’s born get more surviving offspring on average. Over a lot of generations that means that the genes that make an animal instinctively protect their offspring become more and more common in the population.
It doesn’t apply to species that produce a lot of offspring at once (like fish) or can produce offspring every month or so for most of their lives (like rodents). It does apply to species that have a yearly reproductive season, and species that gestate their offspring for many months.
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