There he was — the most handsome man I had ever seen. He entered the room on the first day of class, and the eyes of every heterosexual woman were upon him as he walked casually to his seat. He made even the most sensible woman swoon, and I thought to myself. "Wow, he would be able to impregnate me in no time! I should get his number!"

Laugh if you will, but this is exactly what happens in the female subconscious every time she spies an attractive potential mate. Men, you aren't spared in this either, as your brains also secretly survey the fertility of the women you see.

People go on and on about loving what's on the inside, but there's no doubt that what's on the outside plays a major, albeit subconscious role. Can we overcome our subconscious? Perhaps, but when it comes down to it, attraction is really just an ancient biological trick being played on us. What women and men may consider attractive in a partner is usually just a secret indicator of fertility or virility.

Think of sex symbols in our society. Topping the sexy list are names like Angelina Jolie and Brad Pitt. But what makes them so darn sexy? And why are we so inexplicably drawn to them? It all comes down to biology.

While Brad Pitt is ridiculously attractive, so are many other men in Hollywood. So what is it about Brad Pitt that consistently puts him on Hollywood hot lists? His prominent jaw line, deep voice and broad shoulders are one factor, as are his muscular frame and facial hair. While many people would shrug off Brad's characteristics as "just sexy," they are really all indicators of strong testosterone and therefore an ability to impregnate a partner easily, which, for many women, is too much for their subconscious to resist.

Angelina Jolie is considered by many to be the queen of sexy. But what is it that sets her apart from Paris Hilton? It all comes down to the curve factor — yet another sneaky biological trick. The difference lies in the hips. While both women have a small waist, Jolie has that extra something to give her an hourglass shape. This curvy frame is considered an attractive feature and a strong indicator of fertility and reproductive health in many cultures.

While men are ogling these curvy women thinking "Look at those curves!" their primal subconscious is really thinking "She would definitely be able to carry my baby!"

Many studies have been done on the idea of curviness corresponding to fertility and beauty. Through the years, scientists have developed a hypothesis about curve ratio. A curve ratio is calculated by dividing a woman's waist measurement by her hip measurement. Scientists argue that a ratio that is at or near 0.7 is considered the most desirable in American culture, and is also an indication of an extremely fertile woman.

Facial symmetry is also key. Men who find women to be "pretty" are usually basing this decision on a subconscious observation of facial symmetry. An even and symmetrical face, even down to the smallest millimeter, is a sign of strong estrogen, and therefore, fertility. When a woman is ovulating (the time of the month when she is the most fertile) her face becomes even more symmetrical, and therefore appears to be more attractive to a potential mate.

Facial symmetry isn't the only trick women's bodies use to attract a mate during ovulation. According to a recent article in The New York Daily News, women who are ovulating tend to dress sexier and are more conscious of their appearance during their period of highest fertility.

The article describes a study that followed 30 women over a one-month period. Photographs were taken of the women every day, and at the end of the study, the photographs showed that the women tended to look more casual on days of low fertility, and look very put together during the high fertility days during ovulation. So ladies, the next time you feel compelled to look your best, be careful — you could just be ovulating.

And biology not only plays tricks when it comes to finding a mate, but when it comes to keeping a mate as well.

According to a recent article in the Ontario, Canada-based Hamilton Spectator, humans are genetically programmed to be in long-term relationships. Once a person finds a compatible mate, both people's bodies release the chemicals oxytocin and vasopressin. These feel-good chemicals are nicknamed "cuddle hormones" because of the lovey-dovey behavior they induce. Physical contact with a loved one can increase these levels, and sexual contact sends the cuddle hormone levels off the charts.

While these cuddle hormones make couples feel good, their main purpose is to keep the couple together for child survival purposes. In the wild, mammals that mate and raise a child together have a higher chance of having their offspring survive. For humans today, this is not necessarily true, but the primal biological idea is still there.

The next time you see that beautiful or handsome stranger walking down the street, or find yourself getting just a bit more flirtatious with your neighbor in lecture, think about what it is that is really attracting you. You could find that it is purely biological, a product of millions of years of subconscious reproductive tricks.

Reach columnist Sara Wilson at opinion@thedaily.washington.edu.