Genetic Alteration Keeps Chickens From Caring For Their Eggs
Commercial chickens do not make good parents. It’s not their fault, though. They’ve been bred to care as little as possible about their offspring.
Chickens are brood animals, and they have a natural tendency to sit on the eggs they’ve laid to keep them warm. But this tendency, called broodiness, is a problem for farmers who raise chickens for eggs. The more time a hen spends trying to raise the eggs she’s laid, the less time she spends laying new ones. So farmers have bred broodiness out of commercial chickens.
There's a genetic basis for chickens wanting to take care of their offspring. One particular gene—scientists don’t know exactly which one, but a 2010 study suggests the dopamine receptor D1 (DRD1) gene could play a role—controls whether a hen wants to pluck her own feathers and use them to keep her nest egg warm, or whether she would rather be preening or roosting far from her offspring. When that gene gets bred out of a chicken breed, the hens are more likely to be indifferent to their eggs.
The mutation likely occurred naturally at first, in White Leghorn chickens, but has since been selected for in other breeds, because bad parenting means good money for chicken farmers.