Excerpted from Dr. Peter Adamson’s book Fabulous Faces (available on Amazon.com) and edited for our blog.

We like to think we live in an age when looks don’t matter. We want to believe that it’s not what you are on the outside, but what you are on the inside that counts. But the hard truth is that we can’t fight our genetic makeup. We have descended from tribal “survival of the fittest” societies in which the weak died young. Survival was directly linked with reproductive ability. Those things are no longer inextricably linked in our world today, but our genes don’t know that.

Evolutionary psychologists believe that attractive faces advertise good genes, which want to be passed on. An attractive face is a health certificate proclaiming an individual’s value as a mate. A healthy appearance suggests fertility and reproductive capacity.

Interestingly, psychologists have found that women’s sexual response to attractive men actually increases, with no conscious effort on their part, during the fertile period of their menstrual cycles. At other times, that attraction lessens and women have a soft spot for men with more feminine or “baby-faced” features. In studies, women associated this with warmth, honesty, and a willingness to invest in offspring.

In either case, the first drive of human beings is to survive, and part of that is reproduction. That’s why sex is so important and why fashion and beauty become important. They’re all related to sex.

Most people who want rhinoplasty started to dislike their noses at puberty, when it came time to be accepted by the opposite sex. Darwinian evolutionary thinkers would say that if we don’t want to die, and one of our primal drives is to survive, then certainly we can see by looking at our own skin that we are getting old and will die. We’re on that route. I suspect that, at a very subconscious level, it’s one of the great drivers to look good.

Looking in the mirror involves looking at your own mortality. But it’s also the reflection that you’re most at home with. This reversed image is the one that’s imprinted in your brain. It’s why we feel more comfortable looking at our reflections than at photographs of ourselves.

When others look at you, they don’t see you as you see yourself. They see a slightly different you—they see the photographic you. Which one is real? They both are.