I have posted this picture taken at Parowan Gap, UT before, but I think it deserves another look.
The lower right petroglyph in this picture is thought to be an ancient Native American depiction of pregnancy. The half-circle resembles a pregnant belly and there are 36 marks, indicating the 36 weeks of the gestational cycle. There are 8 marks above and 8 marks below the belly, which total 52 weeks reflecting the entire year. It is thought that the Fremont believed that the mothers and babies had the best chance of survival if they conceived 8 weeks after the summer solstice. Babies would then be born in mid spring, and would be strong enough to survive the following winter.
On the upper left, the fan has 29 lines that symbolize a lunation (a "moon"). The wedge below records four three month quarters, or a year, and below that there are five-and-a-half wavy lines with 16 points, and this is thought to symbolize a full moon.
The culture of the ancestors of North America reflects a far greater understanding of our world than modern man has given them credit for.