By: Charlotte Flores
November, 2023
The chicken population outnumbers that of all other birds on the planet combined, with ~3 chickens for every human on earth at any given time (1). Furthermore, their growing popularity as a source of chicken meat and eggs suggests the current annual slaughter rate of 70 billion chickens will only increase.
Graph from link
<aside> đ§ But how did we get the chickens we know today? The unnatural evolution of modern chickens may surprise youâŚ
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Red Jungle Fowl via Wikipedia
Modern Broiler Chicken via Adobe Stock Photos
The red jungle fowl, a wild bird native to South Asia, is the ancestor of all modern chickens. Both broiler (meat) chickens, and laying hens (egg chickens), have undergone significant morphological changes compared to their ancestors and even pre-industrial domesticated chickens. These transformations are directly attributable to human intervention and selective breeding efforts to increase the efficiency and profitability of the modern poultry industry.
Image Via Link
Selective breeding involves choosing animals or plants to mate in order to produce offspring with the traits we humans want.
The modern broiler chicken itself can be traced back to a marketing ploy by supermarket A&P called âThe Chicken of Tomorrowâ - a selective breeding contest which promised to create âone bird chunky enough for the whole familyâŚall costing less instead of moreâ(2).
The winners of the contest did more than transform chickens, they reinvigorated the chicken industry, setting humans on the insatiable path of prioritizing profits and productivity over all else. As a result, 90% of broiler chicks worldwide can be traced back to 3 companies and this intensive breeding has decreased genetic diversity of chickens by over 50% (3).
Both images via link
Broiler chickens and laying hens have both suffered greatly as a result of artificial selection. The pursuit of rapid growth and high productivity, while beneficial for humans, has come at the expense of the birds' physical and behavioral well-being. Meaning the costs of these alterations arguably outweigh the benefits. We will explore these issues in more detail, but it's important to note that the poultry industry split into two in the mid-twentieth century, with some chickens bred to lay eggs, and others bred for meat. These distinct âflocksâ are genetically different, meaning that the plights of laying hens are different from those of broiler chickens.
Size comparison of meat chickens overtime via ZME Science.
Growth rate comparison of meat chickens overtime via the Association for the Study of Animal Behavior.
Broiler chickens now grow 300% quicker compared to their jungle fowl ancestors (4), meaning they reach slaughter age in just 35 days; half the time it took in 1948 and a stark contrast to jungle fowlâs natural lifespan of 3-11 years (3). Modern broilers are also fattier than chickens of the past, with bodies triple the width and double the length of their ancestors, and breasts 80% larger than their pre-industrialized counterparts (3).
The growth of modern chickens has led to serious health problems, such as leg and joint problems, lameness, and heart failure. (5) If broiler chickens were left to live to maturity without human interference, they would likely die. Even in their short lives, many broiler chickens are unable to move because their legs can't support their abnormal body weight. (6)
Video of a broiler chicken immobilized in a factory farm via iStock.
Video of a broiler chicken immobilized in a factory farm via iStock.
Rapid muscle growth in chickens can damage vital organs and shorten lifespan. This is because the quick growth of leg and breast muscles leads to decreases in the size of other vital organs like the heart and lungs, restricting their function (3). These disorders can also be painful and make it difficult for chickens to move and exercise naturally.