Here’s a nature-nurture question I’ve often wondered about but never quite answered: Why, until the late 20th century, were there so few star baseball players who were the sons of other star baseball players?

Today, it’s common to see grand old baseball names like Yastrzemski, Guerrero, Bichette, and Biggio in the current headlines. But that’s a relatively new phenomenon.

For example, if I sort all the baseball Hall of Famers into order of when they made their debuts, the oldest with a father I can picture is Ken Griffey Jr., who made his big league debut in 1989. (I saw him play side by side in the outfield with his father in the last game ever at old Comiskey Park in 1990.)

Sandy Alomar debuted in 1988, and his dad played some big league ball, but I get him confused with Sandy Amoros.

Also, Barry Bonds will eventually be in the Hall of Fame and he made his debut in 1986. I can recall his father Bobby hitting a grand slam in his first major league game.

But I don’t recognize many older players in the Hall of Fame whose fathers were famous in either the major leagues or the Negro leagues. I am sure I’m missing some. For example, I guess Luis Aparicio’s dad was a famous shortstop in Venezuela.

In contrast, a whole lot of old Hall of Famers had brothers who were pretty good ballplayers.

Several had sons who got cups of coffee in the big leagues: e.g., 1920s star George Sisler had two sons who played in the majors.

Theories:

A. Demographic expansion: 19th century baseball players tended to be the sons of Union Army veterans who had played a lot of ball in army camps during the Civil War, when the previously localized sport standardized on the New York rules.

Around the turn of the century came early Southerners like Ty Cobb, the Georgia Peach, as the North and South reconciled and the South took up the North’s game.

There were a lot of immigrants, then black players and Latin players. Since the 1990s there have a few East Asian players in the MLB, but most guys who play baseball today are from cultures that have been playing baseball for generations now.

B. Having a pitching machine in your backyard is a huge help to becoming a good hitter, but almost nobody had them until the late 20th century. Now, they are common for big leaguers to own one, so their sons benefit.

C. America was so baseball-crazed up until the rise of other sports in the 1960s that you didn’t need to have a Tiger Dad to teach you the fine points of the game (although it didn’t hurt Mickey Mantle). Practically every non-immigrant adult male had played some ball back in the day and could give you pointers. The DiMaggio Brothers’ dad didn’t know anything about baseball, but in San Francisco in 1930 there were lots of other guys to coach. But now the game has become more specialized, so it helps to have a father who played a lot.

Other explanations?