Birds have a quality known as broodiness. It means that, after they lay their eggs, they stick around and take care of those eggs. Most commercial chickens don’t have that quality. And it looks like their complete disregard for their offspring results from one genetic mutation.
Broodiness, in chickens, is not a trait that farmers appreciate. Every minute a hen stays sitting on an egg is a second that she isn’t off producing another egg. Ideally, farmers want hens that will drop an egg and immediately wander off. Even “backyard” chicken farmers prefer chickens that aren’t broody.
This is why many commercial hens have no maternal feeling. They’ve been helped along by farmers, who select against broodiness, but a lack of care for their eggs seems to have started as a mutation in the White Leghorn breed of chicken quite some time ago. What’s amazing about this is researchers believe that it’s flat-out genetic. One gene gets expressed less, and hens leave their eggs to freeze.
Scientists don’t yet know which gene. For some time, they believed that the gene that determined broodiness was on one of the Z sex chromosomes of chickens. Now they believe it autosomal—housed somewhere on one of the chromosomes that don’t determine sex. Somewhere in chicken DNA is a gene that snaps their concern for their children off like a lightswitch. Now I’m not saying the same thing exists in human DNA. Chickens are sometimes model organisms for humans, but they’re mostly studied as models for embryonic vertebrate development. Still, it’s interesting to think that genetics could have a similar effect on us. Could a gene make us entirely unconcerned for our own children?
[Source: Genetics of Broodiness in Poultry]