Changes in semen and the testis

Infertility currently affects at least one man in 20, but we are unable to assess whether it is becoming more prevalent because we have extremely poor past records. Male reproduction has been given little attention scientifically and in medical practice. However, our recent meta-analysis in the BMJ of 61 papers on semen quality, which clearly pointed to a decrease over the past 50 years,1 has been repeatedly quoted in the BMJ,2 3 4 Science,5 and the popular media.

We have already responded to the various technical criticisms, several of which concerned the known limitations of meta-analysis.*RF6-8* Though the data for 1970-90 were compatible with a decrease as well as with no change or an increase in semen quality, the cautious general conclusion is that a real decline in semen quality did occur over the full period 1940-90. Three recent reports have found that semen quality has declined among candidates …