Filet mignon steaks are cut from the tenderloin, a long muscle located on the underside of the animal's spine. It's a rule of thumb in meat production that the least-used muscles are tenderest, and the tenderloin serves only to support the spine. It's a roughly cylindrical muscle, thick at one end and tapered at the other. Filet mignon is cut from the center section, where the muscle's diameter is consistent. It's also small enough there to provide appropriately thick medallions, when cut to standard portion sizes of 4 to 6 ounces.

Diners like tender beef, and young animals produce the tenderest meat. That's why most beef is cut from young heifers and steers. Heifers are immature females, while steers are young males that have been castrated. Castration causes physiological changes in steers, causing them to put on flesh more effectively than heifers and produce more beef for every pound of feed. That's why they account for half of all beef production. Beef heifers are smaller and are usually slaughtered if they aren't needed as breeding stock. They account for approximately 30 percent of beef production, with the remaining 20 percent coming from mature animals.

Minimizing stress on the animals at a processing facility is a major design consideration, not only because it's humane but because stressed animals produce tougher meat. This is especially a problem with heifers, which are more excitable and nervous than steers. This means heifer beef is prone to toughness and is often graded lower than steer beef. That's unfortunate, because heifer beef is well-marbled and flavorful. A 2007 study prepared for the National Cattlemen’s Beef Association by researchers from Colorado State University analyzed some of the factors leading to toughness in heifer beef, so the industry could attempt to address the issue and improve heifer beef's quality and saleability.

The filet mignon portions at your local supermarket or butcher shop are likeliest to come from a steer, for a combination of those reasons. To begin with, more beef comes from steers. Since heifer beef is often graded lower, and heifers are smaller in size, their tenderloin is often incorporated into inexpensive T-bone and porterhouse steaks. That provides retailers with an attractive option for cost-conscious shoppers, while reserving the larger, higher-graded steer beef for costlier steaks or medallions of filet mignon.