Women should be mothers from 19 to 35 and transition to grandmotherhood after 35. Here's a very uncomfortable fact: a 25 year old biological brother and sister having children together have less of a chance of birth defects than a woman over 37. Women older than 35 are not supposed to be having children. Women in their 60s should be great grandmothers. Here's the difference: we are forcing a species that was adapted to tribal existence (60-120 people) to a modern information world where over 50% live in massive cities (which we are not genetically adapted to do).