Why is it the male seahorse that gets pregnant?

The answer

Male seahorses possess a specialized brood pouch on their abdomen into which the female deposits her eggs during an elaborate courtship dance. The male then fertilizes and incubates the eggs, providing oxygen and nutrients through a network of blood vessels in the pouch lining, in a process remarkably similar to mammalian pregnancy. After a gestation period of 14 to 28 days depending on species, the male goes through muscular contractions to expel fully formed miniature seahorses, sometimes hundreds at a time. Scientists believe this role reversal may have evolved because it allows faster reproduction, since the female can prepare more eggs while the male gestates the previous batch.