Man has gone through a lot of changes throughout history and these include evolutions in physical traits and personalities. What helped change man's facial features and gave him gentler and more cooperative personalities, however, which are believed to have contributed to the development of modern society apparently lies on changes in his testosterone level.

A new study led by University of Utah graduate student Robert Cieri suggests that man's transition to modern civilization has something to do with the species' lowered testosterone level as the drop of testosterone in humans approximately 50,000 years ago coincided with the development of arts and advanced tools which include fishing equipment, grindstones and projectile weapons.

For the study published in the August issue of the Current Anthropology, Cieri and his team examined the features of over 1,400 modern and ancient skulls and found that heavy brows started to fade out and rounder heads become more common approximately 50,000 years ago, which is marked by the introduction of advanced tools and symbolic artifacts, and these physical traits are associated with modern humans who have lower testosterone levels.

"Human fossils from after modern behavior became common have more feminine faces, and differences between the younger and older fossils are similar to those between faces of people with higher and lower testosterone levels living today," Cieri said.

Cieri said that lower levels of testosterone is linked with social tolerance and cooperation among animals and less aggression in humans and opined that the increasing human population may have been responsible to the drop in man's testosterone level as people need to cooperate with each other to succeed and aggression can be a disadvantage.

Although it isn't clear what really caused the reduction of testosterone levels, Cieri said that the phenomenon allowed people to learn better from each other and work with each other which have sped up cultural and technological innovations.

Cieri said that the birth of modern human behaviors came at a time when man has developed a more cooperative temperament, which suggests that the changes brought about by lowered testosterone levels have helped pave way to the modern civilization we have today.

"We argue that temporal changes in human craniofacial morphology reflect reductions in average androgen reactivity (lower levels of adult circulating testosterone or reduced androgen receptor densities), which in turn reflect the evolution of enhanced social tolerance since the Middle Pleistocene," Cieri and colleagues wrote.