When it comes to men identifying women that they want as sex partners whether it’s for a one-night stand, or a long-term relationship they are slaves to their biological programming. (Women are, too, but in different ways.)

A field of science called “evolutionary biology” explains how many of our thoughts, feelings and behaviors are driven by our biology, otherwise known as our “human nature.” Over the eons, our bodies and minds have adapted to solve various problems of survival and reproduction. This is especially true when it comes to how we choose our sex partners.

When a guy is out at a bar scoping out the “talent,” he believes his goal is to meet a pretty girl. But on a subconscious level, his mission is more specific: he wants to find a healthy, fertile woman to mate with. That is what his brain is telling him to do: to carry out the man’s biological mandate, which is to have sex, conceive children, and carry on his genetic legacy.

The experts say that the most sexually attractive women, from an evolutionary standpoint, are “blonde bombshells.” From Marilyn Monroe to Farrah Fawcett and Anna Nicole Smith, from Pamela Anderson to Britney Spears (back when they were younger and hotter), to the actress Scarlett Johansson and Hugh Hefner’s gaggle of girlfriends, there’s something about young, blonde women of certain proportions that men instinctively find very attractive.

Women are aware of this. Way back in 15th- and 16th- century Italy, women were dying their hair blond not because it was the “fashionable” thing to do, but because they understood that it made them more attractive to men. In recent times, a study showed that in Iran, the women are actually more concerned with their body image, and want to lose more weight, than their American counterparts.

Since Iranian women are generally not exposed to Western television and movies, how do you explain this desire to fit this definition of beauty? It’s because over the centuries, women have evolved to know instinctively what makes men want to mate with them. Thousands of years ago, the ancestors of theirs who fit that physical mold were the ones who successfully attracted men and reproduced.

So what is it about long, blonde hair that commands men’s attention? Evolutionary biologists say it’s because lustrous, shiny hair is an indicator of good health, which men read as “fertile” (i.e. they can get impregnated easily). Because hair grows slowly, a woman whose hair is shoulder-length, or longer, is a sign of at least several years of healthiness. The blond color, meanwhile, signifies they are still young, since young girls with light blond hair usually become women with brown hair. My next article will dwell more on this topic and why men love blondes.