The loss of penis spines and facial whiskers is what puts humans a step ahead of chimpanzees on the evolutionary ladder, according to scientists.

Understanding these subtle genetic differences, along with other small changes that occured over a span of millions of years, may get scientists closer to pinpointing exactly what it means to be human.

Biological anthologists in the US can be accredited to the findings that change the way we think about our species: it’s not what we’ve gained over the years that sets us apart, but what we’ve lost.

When the human genome was first decoded over a decade ago, scientists expected to isolate a series of “human genes” responsible for our unique characteristics, primarily our intellectual edge. Instead, they discovered that it’s a lack of certain genes that makes us what we are.

The loss of certain primal characteristics, like a small, sensitive spine at the tip of the penis, has encouraged human features to evolve.

Penile spines, which are present in chimpanzees and other non-human primates, aid in rapidly impregnating mates by increasing sensitivity and speed of ejaculation. In a highly competitive sexual situation, it is beneficial characteristic for the organism to have.

Humans, however, have evolved to benefit from long-lasting monogamous relationships that do not require rapid impregnation. In turn, monogamous relationships have paved the way for the complex social structures, which have helped foster our increased intelligence.

Scientists are still finding out ways we differ from our primate cousins and hope these findings will further our understanding of humanhood.

“There are going to be many different features that make humans unique and I don’t think we’re close to describing all the links between genes that make us different from chimpanzees,” said Reno. “We are just getting the initial picture.”