A new study suggests that the more brothers a man has, the faster their sperm is, which mean greater fertility.
Researchers assessed the fertility of 500 men and found that sperm swimming speed had to with family genetics!
Apparently slow and steady isn't in these sperm's vocabulary
"We found the greater number of brothers rather than sisters a man has, the faster his sperm is, increasing the likelihood of fertility. Lots of brothers is also an indication that the man's parents have strong male fertility genes, and they would then be passed on to the son."
However, if you don't have a brother that doesn't mean you need to start timing your sperms!
Here's what the same scientist said:
"This is certainly not a smoking gun as a reason for infertility in men. However, it would be interesting to test whether the same relationships are observed in other human populations as well as in other species. Likewise, would we observe similar associations when looking at female fertility?"
You're the scientist - you tell us!