In my public health course, statistics and human anatomy basics were part of units. In statistics, I was taught how to apply it, to analyze and evaluate a phenomena and projects to mention but a view from which we can draw useful conclusion-informed decisions.
It is from this statistics perspective, I opines anatomists tabulated menstrual cycle of 21 and 35 days shorted and longest days respectively, and 28 days as the arithmetic mean from discrete variables sampling, measures of average, central tendency or location.
At the 14th-16th day of the cycle, the ovum is extruded into the abdominal cavity. This is the process of ovulation [fertile days]. Well, hallmark of lovemaking is offspring. Or,imagine a Valentine day on menstrual phase-characterized by vaginal bleeding and last 2-7 days according in what I learnt in human anatomy class.
So, it’s not a coincidence, in my view, that, Valentine’s Day is commemorated in month of February, which is 28 days month to corresponding with 28 days menstrual cycle arithmetic mean, save for limp year of 29 days albeit within the range also.
In nutshell, month of February has 28 days at four year cycle, an average integer of menstrual cycle, hence fertile day falling on day fourteen convenience for both natural lubrication and reproduction since females are hormonal attracted to males.