One of the most compelling arguments for this nexus lies in the concept of evolutionary "spandrels"—byproducts of evolution that turn out to be essential. When testosterone levels spike in a population due to environmental pressure (such as high competition for mates), it triggers a cascade of genetic expressions.
These are not arbitrary decorations. They are of genetic quality. High-testosterone males grow larger weapons and brighter ornaments—but only if they have the underlying health to pay the immune cost. Females, over millions of years, evolved to read these signals. They choose the male whose testosterone nexus screams: "I am so strong that even with a suppressed immune system, I am still alive." secret testosterone nexus of evolution