A new study published in the Journal Proceedings of the National Academy of Science suggested that men with bigger testicles tend to have poor parenting skills than fathers with smaller testicles. The findings of the study are correlational. Scientists can't exactly explain why there is a connection with testicles and parenting skills. They only know that there is a link between the two.

Men who have bigger testicles produce more sperm cells and sperm production requires a lot of energy from the body. James Rilling, co-author of the study, said that fathers with bigger testicles may be facing a "trade-off between investing energy in parenting and in mating." Mr Rilling is an anthropologist at the Emory University in Atlanta, US.

Many studies have proved that children with more caring and involved fathers have better emotional understanding, social interactions and education. Mr Rilling and his co-researchers were interested in understanding why some men are better fathers while others are absent from their children's lives.

In 2011, a study conducted in the Philippines has suggested that males with higher levels of testosterone will be more likely to marry than men with low testosterone levels. However, men who become eventually involved in taking care of their children may see their testosterone levels decline than men who distance themselves after their wives give birth.

Testosterone plays many roles in the male body and the study did not clearly indicate whether the falling male hormones was due to more time in being better fathers than better mates. The study used data gathered from the 70 married men between the ages of 21 and 55. All the men had one to four children. The survey results showed that only four men did more childcare duties than their wives.

The researchers scanned the brains of the fathers using magnetic resonance imaging (MRI) as they looked at photos of their children. The research team also measured their testosterone levels by taking their blood samples and scanned their testes to determine the volume. The volume of men's testicles varied considerably - the smallest was a little more than a tablespoon while the biggest can fit a quarter cup.

The researchers discovered that men with bigger testes were less involved in parenting. Brain scans showed less brain activity when looking at images of their children. Less-involved fathers also had higher testosterone levels, according to the study.

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