Over the past 50 years, human sperm counts appear to have fallen by more than 50% around the globe, according to an updated review of medical literature. The review, and its conclusions, have sparked a debate among experts in male fertility. "I think one of the fundamental functions of any species is reproduction. So I think if there is a signal that reproduction is in decline, I think that's a very important finding," said Dr. Michael Eisenberg, a urologist with Stanford Medicine who was not involved in the review. "There is a strong link between a man's reproductive health and his overall health. So it could also speak to that too, that maybe we're not as healthy as we once were," he said. The new analysis updates a review published in 2017 and for the first time includes new data from Central and South America, Asia and Africa. It was published in the journal Human Reproduction Update. An international team of researchers combed through nearly 3,000 studies that recorded men's sperm counts and were published between 2014 and 2020. Overall, the researchers determined that sperm counts fell by sightly more than 1% per year between 1973 and 2018. The study concluded that globally, the average sperm count had fallen 52% by 2018. When the study researchers restricted their analysis to certain years, they found that the decline in sperm counts seemed to be accelerating, from an average of 1.16% per year after 1973 to 2.64% per year after 2020.