If you have roast turkey for Thanksgiving, you have your choice of light meat or dark. With wild turkeys, you only get dark meat. Why?
The difference between the light meat and dark meat on a turkey is a substance called myoglobin. Myoglobin stores oxygen in the muscle, to keep the muscle from running low on oxygen during strenuous exercise. Muscles that are used a lot develop more myoglobin, and a dark color. Muscles that are not used much have less myoglobin, and a lighter color. Domestic turkeys don't fly, so their breast and wing muscles have little myoglobin and are light colored. Wild turkeys do fly, so all of their muscles are darker meat.