quote: The complex study came to these conclusions by looking at the medical records of 2,238 female participants, spread across two generations (starting in 1948) and looking at their medical history when they reached menopause. The study examined those that successfully reproduced and looked at what traits influenced their reproductive success. It also made adjustments for income, education and lifestyle choices such as smoking, before applying correlations to determine the direction of evolution. They also looked at secondary effects, i.e. whether low blood pressure led to younger sexual maturity, or whether the paths were independent.