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POPSIs it so different? "After the female deposits her unfertilized eggs into the male, the outer shell of the eggs breaks down, and tissue from the male grows up around the eggs in the pouch. After fertilizing the eggs, the male closely controls the prenatal environment of the embryos in his pouch. The male keeps blood flowing around the embryos, controls the salt concentrations in the pouch, and provides oxygen and nutrition to the developing offspring through a placenta-like structure until he gives birth." " in some species of pipefish, the sex roles are reversed because males become pregnant and there is limited brood pouch space. So females compete for access to available males, and thus secondary sex traits (such as brightly colored ornamentation) evolve in female pipefish instead of males."
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POPSIs Monogamy Natural? "Lots of animals," Quirk says, "have the 'marriage' instinct: penguins, parrots, swans, gibbons, seahorses, humans. ... What do all these animals have in common? Long childhoods. Who has the longest childhood in the animal kingdom? Humans."