For more than four decades, Robert D. Martin, the Field Museum’s A. Watson Armour III Curator of Biological Anthropology, has studied primates for the clues they provide about humanity. He gives his science-based take on how nature intended such things as sex, childbirth and parenting to go in “How We Do It: The Evolution and Future of Human Reproduction.” The book hits stores Tuesday.

This is his first book meant for a general audience, so we asked Martin, who has successfully reared three children with some help from lessons he learned from the animal kingdom, to help sort through five myths about children — child-making, child-birthing and child-raising.

Myth #1: Sperm swim, competing against each other like Olympians searching for gold.

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Martin: “The classical idea is it’s like a race, like a sprint race, and the fastest sperm wins. It doesn’t work like that at all.” Martin explains that pumping in the womb and oviducts moves the sperm more than a swimming sprint.

Myth #2: It’s optimal for women to breastfeed for one year.

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Martin: Three years is what nature intended, with supplementary foods given in the second and third years. “My message is not that a woman should breastfeed for three years. My message is that human milk has a special composition because the baby’s brain develops very rapidly during the first year after birth. So the milk the mother provides has to contain what the working brain needs. And that hasn’t been taken into account enough in designing milk formulas.”

Myth #3: Want to get pregnant (or not)? Assume you are ovulating on the 14th day of your cycle.

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Martin: “If you look at the cycle, the first thing is the timing of ovulation is a lot more variable than people think. It’s a moving target. Ovulation is not fixed on day 14. ... Women can actually conceive on any day of the cycle. It’s a probability function.”

Myth #4: Children cannot be potty trained until they are about 2 years old.

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Martin: “Potty training is unique to humans. I came across this study in Africa that showed this society where they trained babies really early on, a few months after birth. ... My wife doesn’t believe what I’ve written. She says it sounds like rubbish. She will not accept it. ... We don’t know how long people have been doing potty training. All other primates simply go where they are. If I were to start all over again with the knowledge I have now, I would try early toilet training.”

Myth #5: Sperm counts have remained consistent over time.

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Martin: Sperm counts for men in many industrialized areas are declining. “You wouldn’t expect them to change. That is not true, and there are lots of human populations where sperm counts are now half of what they were 50 years ago. I think it’s environmental toxins that’s having the effect. The implications for infertility are pretty dramatic. [Declining sperm count] is pretty controversial and, like global warming, you have people saying it isn’t happening.”

So much for the story about the stork...

'Expert debunks myths about where babies come from' had my hope us.

The lower sperm count brings to mind a clipping I saved about 30 years ago, saying that college men in dorms had low sperm counts, and a chemistry professor in Florida believed that he tracked it to the fire-retarding chemicals on mattresses (required by law!). He visited dorms and found that many guys were sleeping directly on them with no sheets. He got sued by the chemical industry and had to retract, or spend gazillions fighting his findings.

When I was in college in the mid-'60s, the rumor was that cafeteria staff lined the sheet cake pans with saltpeter to suppress male ardor.