In the 1950s, a competition was held to create the “chicken of tomorrow” through selective breeding. This is the path that got us to the modern broiler chicken. Unlike their recent ancestors (and much unlike their distant ones) these birds grow so large so quickly that they are prone to health issues and disease.

This is a quick and interesting read: https://exhibits.library.cornell.edu/backyard-revival-american-heritage-poultry/feature/the-chicken-of-tomorrow