Scientists have discovered how much chickens favor good looks in the opposite sex - after finding that the hen with the largest comb gets more attention from roosters

And ironically, this hen attraction can be blamed on humans - for it is our desire for eggs which led to the ingrained behavior. Researchers say that our methods of breeding hens in pursuit of the perfect egg gives us more influence over chicken genes than natural selection. Over generations of favoring chickens which lay more eggs, this has influenced the size of the domestic fowl. Compared with the original wild jungle hen, domestic hens have larger combs as well as denser bones. This influences egg-laying, as the hen's bone tissues provide calcium for the eggshells - so the greater the bone mass, the more eggs she can lay. After spotting a clear correlation between comb size and bone mass in chickens from a cross between red jungle fowl and domestic chicken, the research group set up a study where such chickens were crossed for several generations. The researchers were able to identify two genes connected to each other that influence several characteristics simultaneously. By regulating the production of cartilage, these genes influence combs (which consist of cartilage throughout) as well as bone growth (where cartilage is the base material) and, ultimately, egg production. The original hens had smaller combs, thinner legs, and laid fewer eggs. When people bred for the characteristic of laying many eggs, the comb grew automatically. In nature, the comb is an example of a sexual ornament. Individuals with the most impressive ornaments are favored by the opposite sex, thereby obtaining more numerous offspring than their competitors.