Sexual selection is a form of natural selection.

It serves as an environmental force on the opposite sex.

In order to understand sexual selection, you first need to understand parental investment: cost-benefit.

Gamete production and parental care. Female versus male.

Egg versus sperm. Caring for offspring.

Therefore, to increase fitness (pass on genes), males should copulate with as many females as possible. Quantity over quality.

Females should be choosier about mate. Quality over quantity.

Therefore, males will compete for valuable resource (female) and characteristics will be selected for like: horns, size, and muscles.

Female choosiness will also act as a selective force: male attractiveness.

So, the males that out compete with other males for females will have a better chance of passing on their genes and whatever traits that help them out- compete other males to future populations.

In polygamous mating systems, this selection process becomes exaggerated because there is more male competition and female choosiness. In monogamy males and females are more equally choosy, so differences between sexes are less. Their fitness is linked more.

But still, men and women do choose mates, and we have some behaviors that attract the opposite mate that are similar to other species….…like what? Darwin himself suggested that dance has been shaped by sexual selection, an evolutionary process that favors showy traits, such as peacock tails, that attract mates.

For dance to serve as an example of sexual selection, the performance has to reveal something about the innate physical quality of the dancer.

REPHRASE THIS STATEMENT SO YOU FULLY UNDERSTAND IT. DO YOU HAVE ANY POSSIBLE IDEAS OF WHICH PHYSICAL QUALITIES?

To test for such hints, scientists turned to people in Southfield, Jamaica, who had been tested for physical symmetry in a long-term study by Robert Trivers of Rutgers University in New Brunswick, N.J. A controversial theory has argued that asymmetries, say in ear size, indicate developmental shortcomings that make the individual get sick more easily and reproduce less successfully than a symmetrical person.

WHAT OBSERVATION IN NATURE SUPPORTS THIS THEORY? The theory may explain why there is so much symmetry in faces, body…. and nature. Perhaps asymmetry has been selected against. Orlando Bloom, Catherine Zita Jones examples.

WITH THIS STUDY GROUP IN JAMAICA, HOW WOULD YOU LIKE TO TEST THE HYPOTHESIS THAT DANCE IN HUMANS IS AN EXAMPLE OF SEXUAL SELECTION?

William Brown and Lee Cronk of Rutgers and their colleagues used cameras to track laser reflectors fastened on people and then made 40 animations of young Jamaicans dancing to the same pop song. The animations didn't reveal the dancer. WHY IS THIS IMPORTANT? The researchers then asked 155 other young Jamaican men and women to rate how well the animated characters danced.

SHOW VIDEOS Observers ranked the dances most highly when the person behind the animations belonged to the high-symmetry group, Brown and his colleagues, including Trivers, report in the Dec. 22, 2005 Nature.

WHAT DOES THIS SHOW?

So, a head-turning dance style may be a good way to choose a partner

DO YOU THINK MEN OBSERVERS RANKED THE SYMMETRICAL FEMALE DANCERS HIGHER THAN THE WOMEN OBSERVERS DID FOR THE MEN? DEFEND YOUR ANSWER.

There was a stronger correlation between male symmetry and dancing ability according to women observers. In other words, males compete, females choose.