when the baby is born, whereas the man might’ve flown the coop. A caregiver might need higher protection from disease. Women generally have more body fat than men, so perhaps they have more immune system cells, Dr. Hahn postulated to me. She also noted that many of the genes that are associated with lupus and rheumatoid arthritis are on the X chromosome. (Women have two X chromosomes, whereas men have one X and one Y.)
