Chickens have always lived in groups, and in the modern egg production industry they are crammed inhumanely into cages usually containing nine to twelve hens. [Biologist William Muir] wanted to increase egg production by selective breeding, and he tried to do it in two ways. The first method involved selecting the most productive hen from each of a number of cages to breed the next generation of hens. The second method involved selecting all the hens from the most productive cages to breed the next generation of hens.
When Bill presented his results at a scientific conference that I attended several years ago, he showed a slide of hens selected by the first method after six generations.
The audience gasped.
Inside the cage were only three hens, not nine, because the other six hens had been murdered. The three survivors had plucked each other during their incessant attacks and were now nearly featherless… What happened? The most productive individuals had achieved their success by suppressing the productivity of their cagemates.