62% of Americans oppose allowing boys who identify as female to compete in girls' sports: Gallup

Data are scant, since with only about 50,000 post-surgical transgender people in the U.S., they’re a distinct minority. Hard to do statistics on this, but here are some points of reference.

During the Cold War, the IOC didn’t do good steroid testing, and hence the Warsaw Pact took full advantage of that. In 1990, the testing regime was upgraded along with the fall of the Berlin Wall and the end of the East German athletics program. At that time, there was, for both swimming and track and field, about a 2% advantage of the steroid era vs. the “better testing” era that followed. In contrast, mens’ times were uniformly about 10% better than womens’ times. This suggests the difference between male and female performance in athletics is not just testosterone.

In recent years, two transgender (pre-op) runners won a combined 15 titles in Connecticut track & field as girls. Also, in NCAA division 2, runner CeCe Telfer was mid-range NCAA D2 as a male, but after declaring herself/himself transgender won championships in the womens’ 400m intermediate hurdles with a time that would have put her in the finals in NCAA Division 1. This suggests, again, that there are advantages beyond testosterone for those who are born male.

In basketball, a 54 year old (but a tall one) walked on to a college womens’ basketball team and became their starting center. In cycling, a post-op transgender woman started winning titles that she’d never dreamed of as a male.

Finally, in weightlifting, men’s WRs are about 25% higher than womens’, and when Laurel Hubbard became transgender, she kept lifting about the same weight that she had 20 years earlier as a male. It’s a bit complicated—weightlifters tend to get better into their thirties, and during that time Hubbard was having some serious personal issues—but the fact that she/he is lifting the same at age 43 as he did at age 20 suggests, again, that there’s something beyond mere testosterone that explains athletic performance.

Long and short of it is that there appears to be some “shift” between mens’ and womens’ athletic performance that is not merely the result of hormones, so if we allow male-female trans athletes to compete as women, we will find that the “trans” athletes garner far more awards than their numbers and demographics would predict.

Will it “ruin” womens’ sport? I guess that depends on how many trans athletes are out there, and what the response of the fans is, and how athletes who are born female feel about competing against those who were born male. That can be debated. What seems strongly likely, though, is that it would significantly change womens’ sport.