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From 1957 to 2005, broiler growth increased by over 400%, with a concurrent 50% reduction in feed conversion ratio, corresponding to a an annual rate of increase in 42 d live BW of 3.30%. Forty-two-day FCR decreased by 2.55% each year over the same 48-yr period. Pectoralis major (chest muscle) growth potential increased, whereas abdominal fat decreased due to genetic selection pressure over the same time period. From 1957 to 2005, pectoralis major yield at 42 d of age was 79% higher in males and 85% higher in females. Over almost 50 years of commercial quantitative genetic selection pressure, the intended beneficial changes have been indeed achieved.