You can learn about your ancestry using one of several genetic testing services, but none of these services will identify the ancestor we share with all other animals with placentas. Soon after the catastrophic demise of the dinosaurs, a small mouse-like creature appeared. That creature is the likely ancestor to humans, elephants, bears, whales, bats and all other animals with placentas that keep fetuses alive. A new theory suggests that having a placenta contributes to why women have much higher rates of autoimmune diseases than men.
In the United States, 80 percent of the 50 million people with autoimmune disease are women. This is a startling statistic. When you look at specific diseases, women account for 80 percent to 95 percent of patients with primary Sjögren’s syndrome, systemic lupus erythematosus, primary biliary cirrhosis, autoimmune thyroid disease and systemic sclerosis, and about 60 percent of arthritis and multiple sclerosis patients. The thing that links all these diseases is that the patient’s immune system attacks their own cells, either across the entire body or in specific organs.