Outline the function of progesterone in the human menstrual cycle.
An investigation was done to find the effect of the diet of pregnant female rats on the mean age at which puberty began in their female offspring. The pregnant female rats were given either a high fat diet or a normal diet. Their offspring were also given either a high fat diet or a normal diet. The percentage of offspring that had reached puberty was recorded at intervals until the offspring were 39 days old. The results are shown in Fig. 5.1.
State the age at which $50\%$ of offspring had reached puberty when both the mother and her offspring were fed a normal diet.
Over the 20th century, the average age at which puberty began in European girls fell from about $17$ years to about $12$ years of age. It has been proposed that a more nutrient-rich diet was largely responsible for this fall. Using the data in Fig. 5.1, discuss the evidence that changes in diet may have caused this decrease in the age of onset of puberty in European girls.