From 1948 to the present, selective breeding made your dinner what it is today.

You may not know it, but the popularity of chicken in the U.S. is partially due to its being one of the few proteins not rationed here during World War II. But chickens of today are so different from the chickens that existed just 50 years ago, your great-grandparents might not even recognize them.

As you can see in the image above (courtesy of Poultry Science, with breed dates added by Vox), chickens have gotten a whole lot bigger over a relatively short period of time.

To understand how they got this way, it’s important to have a little context for that graphic.

A Brief History of U.S. Commercial Chickens

Photo: North Carolina State University Library

Back in 1948, the biggest supermarket chain in the U.S. was called A&P, or the Great Atlantic & Pacific Tea Company. The chain held a “Chicken of Tomorrow” contest, inviting farmers all over the country to participate. The purpose, according to Modern Farmer, was “development of superior meat-type chickens.”

The winning chicken would have more meat all around, but the most important thing was more white meat. The winning chicken should also grow faster. With these criteria in mind, farmers all over set about their work.

Until 1948, Modern Farmer tells us , only eating them as a special treat once each chicken had gotten past its egg-laying years. As chicken meat rose in popularity, farmers would raise chickens for two distinct jobs: “layers” were bred to lay as many eggs as possible, while “broilers” were bred for desirable meat traits.

The contest worked its way through stages, and 40 finalists submitted a total of 720 eggs to the contest, which hatched, raised, monitored, and eventually slaughtered and judged each chicken.

Photo: Terrierman

The winners: Arbor Acres White Rocks chickens and Vantress Hatchery’s Red Cornish crosses. Those two winning breeds were crossed, creating the Arbor Acre breed—which is the grandmama of most commercial meat chickens raised throughout the world today. As of 2013, over 50% of commercial chickens raised in China have genetic links to the Arbor Acres breed.

Through the process of selective breeding, Arbor Acres managed to cultivate desirable characteristics in chickens. Broader breasts, limited feathering to make plucking easier, increased docility, and increased feed-to-meat ratio are all things that evolved very quickly over successive chicken generations.

Smithsonian Magazine adds that fortifying feed with antibiotics and vitamins was crucial to the rising dominance of chicken on the dinner table, since it made indoor factory farming of chickens possible.

Where Chickens Are At Now

Photo: Flickr/Jules

Today’s chickens now require slightly under two pounds of feed for every pound of meat they yield. That’s less than half the feed-to-weight ratio of a 1945 chicken, according to Smithsonian Mag. Chicken finally surpassed beef as the most widely consumed meat in America in the 1990s; we now eat about 80 pounds per person per year.

Additionally, a modern chicken farmer can now take a day-old chick and grow a five-pound broiler in just six weeks—less than half the time it would have taken 50 years ago.

This massive change in both genetic chicken traits and farming practices has had some down sides, too: massive stress, heart problems, and other health problems are unfortunately associated with these bigger, heavier birds.

Vox called our attention to a recent paper published in the journal Poultry Science by researchers at the University of Alberta. In it, the researchers raised the three chickens you see in the graphic at the top of this piece on the exact same diet, for the same length of time, and under the same conditions. You’re seeing the visual effects of selective breeding at work, over a relatively short span of time.

The Future of Chicken

Chicken is now such a popular meat worldwide, it’s difficult to think of most modern cuisines without it.

But we’re not done building a better chicken yet. Scientists at the University of Delaware, led by geneticist Carl Schmidt, have been figuring out how to breed heat-resistant chickens.

Photo: Modern Farmer

The reason? Climate change. In a separate piece, Modern Farmer tells us that poultry that grows in south-of-the-Equator countries like Uganda and Brazil manages to stay cool in extreme heat because they have featherless necks and heads.

Mapping out the chicken genome is the first step; figuring out how to selectively breed these heat-resistance traits into commercially viable chicken stock is the next. This project is taking place under a five-year, $4.7 M climate change grant from the National Institute of Food and Agriculture.

Schmidt explains,

“Doing this is going to take time. It could take two decades of research before resulting in any actual chickens. You talk to farmers today and they’re not concerned. These people are thinking one flock, one generation at a time. But that’s the reason this kind of work needs to take place in an academic environment. Is it important for next year? Probably not. But is it important a decade or so down the line? Absolutely.”

[via Modern Farmer, Smithsonian Magazine]

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