A 1992 British study of sperm quality in men worldwide has also revealed that the concentration of spermatozoa in the sperm of men today has fallen by half compared with 50 years ago, to 60 million per milliliter. And when spermatozoa lack competitors, their motility declines by half.
一九九二年，英國針對全球男性精蟲品質的抽樣調查也發現，今天男性的精蟲數與五十年前相比少了一半，降到每西西六千六百萬，而精蟲少了競爭對手，活動力也衰退一半。