Once females are liberated from the physiological responsibilities of pregnancy and lactation, as in the rest of the animal kingdom, dads become much more devoted. Amongst birds, bi-parental care represents the overwhelming majority, with 90 per cent of avian couples sharing the load. Slide back along the evolutionary scale and paternal care becomes not only more common, but customary. Amongst fish, it’s single dads that do all the nursing in almost two thirds of species, with mums doing little more than donating eggs before disappearing for ever. Some, like the male seahorse, even give
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