Scientists are struggling to find out why, across the globe, men are becoming increasingly less fertile.

One meta-analysis concluded from hundreds of other studies that there is a “significant decline in sperm counts” in men over the past 40 years.

There are numerous reasons why a man and a woman may not be able to conceive, but most of the time a definitive cause can be pinned down.

But one new study suggests a new factor that may be linked to a man’s ability to conceive children: the size of his penis.

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