I recently read an article that took an in depth look at male testicle size and childcare.The article theorized that men with smaller balls = better fathers.
A study by Emery university was conducted on a group of 70 men from various ages. The test measured testicular volume, testosterone levels and the subjects interest in childcare. Prior studies have suggested that men with high testosterone were likely to be more party oriented and less into parenting, but until recently there were no studies to prove that hypothesis.
The study published in the Proceedings of the National Academy of Sciences is the first independent study showing a correlation between testicular volume and interest in parenting. By testicular volume I mean "size" and the reason size is important is because the bigger the testicle size the more semen that can be produced, per ejaculation. What this means in layman's terms is that regardless of age, men with large balls have more testosterone in their system and less interest in parenting.
Don't take my words out of context. Just because a man has large testicles, it doesn't mean he will be a bad father. What the study demonstrates is that men with smaller testicles are more invested into being a father. While men with larger testicles are more invested in making the babies. For more information check out the video below.