There are few animals more bizarre than the anglerfish, a species that has so much trouble finding a mate that when the male and female do connect underwater, males actually fuse their tissue with the females for life. After the merger, the two share a single respiratory and digestive system.
Now scientists have discovered that the anglerfish accomplishes this sexual parasitism because it has lost a key part of its immune system, which then allows two bodies to become one without tissue rejection. (Remember symbiont Jadzia Dax of Deep Space Nine?)
All vertebrates, including humans, have two kinds of immune systems. The first is the innate system, which responds quickly to attacks by microscopic invaders with a variety of chemicals like mucous physical barriers like hair and skin, and disease-munching cells called macrophages. The second line of defense is an adaptive system that produces both “killer” T