Correlation of scrotal temperature in twins.
Plain-language summary
This study asked why men differ so much in how warm their testicles run. Scrotal skin temperature was logged every five minutes for 24 hours in 48 men, made up of identical twins, non-identical twins and ordinary brothers, and the readings within each pair were compared. Identical twins matched each other closely. Non-identical twins and ordinary brothers did not show a significant match, and the same pattern held at other points in each man's temperature range as well as at his typical reading. The authors read that as a genetic component to scrotal temperature, which would make it a route by which fertility runs in families separately from anything to do with how the sperm-producing tissue itself is built. It comes from the same Danish research program and the same measurement method as the study of temperature and semen quality already in this library.
Key findings
- Scrotal temperature matched closely between identical twins.
- Non-identical twins and ordinary brothers did not show a significant match.
- The same pattern held at other points in the temperature range.
- The study measured temperature only and did not measure semen quality.
How to analyze the study yourself
- Study type
- This compared pairs of related men measured once each, which is a standard way to separate inherited from acquired variation, and it shows nothing about what any of it does to fertility.
- Population
- Forty-eight men, made up of identical twins, non-identical twins and single-born brothers.
- Funding
- Not reported
- Takeaway
- This study found that identical twins run at closely matched scrotal temperatures while non-identical twins and ordinary brothers do not, which points to a real inherited component in how warm a man's testicles sit. It measured no semen, so it says nothing about whose sperm is better. The use of it is that a man who runs warm is partly built that way rather than doing something wrong, and that whatever he changes sits on top of a baseline he did not choose.