Human Females Menstruate to Eliminate Unviable Fetuses

From a female perspective, pregnancy is always a huge investment. Even more so if her species has a hemochorial placenta. Once that placenta is in place, she not only loses full control of her own hormones, she also risks hemorrhage when it comes out. So it makes sense that females want to screen embryos very, very carefully. Going through pregnancy with a weak, inviable or even sub-par fetus isn't worth it. That's where the endometrium comes in. You've probably read about how the endometriu...

 BIDS Approach to Understanding Intelligence

There is nothing really the matter with the concept of g; it is just that we have misused it by making it the omnipresent concept in our study of cognitive abilities. Intelligence is important on three levels, namely, brain physiology, individual differences, and social trends (collectively, BIDS). The core of a BIDS approach to intelligence is that each of those levels has its own organizing concept, and it is a mistake to impose the architectonic concept of one level on another. We have to ...

 Invasive Blood-Seeking Fetuses in Mammals

In most mammals, the mother’s blood supply remains safely isolated from the foetus. It passes its nutrients to the foetus through a filter, which the mother controls. The mother is a despot: she provides only what she chooses, which makes her largely invulnerable to paternal manipulation during pregnancy. In primates and mice, it’s a different story. Cells from the invading placenta digest their way through the endometrial surface, puncturing the mother’s arteries, swarming inside and ...