Anthro2050 1st Edition Lecture 7 Outline of Last Lecture I Evolution and Tinkering II Sexual Selection Outline of Current Lecture II Sexual Selection Continued III Humans and Sexual Selection Current Lecture Sexual Selection Continued in some animals males engage in direct physical combat to attract and win access to females therefore they develop traits that help them to win these contests including size antlers tusks large canines strength etc sometimes there are traits used to attract mates that are not used in physical combat yet rather a physical indicator of good health or good genes such as long tails in some birds however some adaptations due to sexual selection are maladaptive to survival and natural selection i e if birds with long tails grow tails too long it could be harder to fly and easier for predators to grab them there are some theories as to why natural selection would allow sexual selection to develop traits that could make them more susceptible to predators The Good Genes Model suggests that these traits signal good genes and good health For example the traits human males tend to find attractive in human females shiny hair clear skin clear eyes a certain hip to waist ratio are associated directly with fertility and good health The Pre Existing Sensory Bias Model suggests that there is a predisposed neurological disposition to just like certain traits For example in some bird species males have big colorful crests on their heads that seem to attract females In bird species where these crests do not These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute naturally occur males with artificial crests attached attract more males than the natural ones without Another characteristic of sexual selection is sexual dimorphism In species where competition between males is high and the animals practice forms of polygyny the sexual dimorphism is high However in monogamous species where competition is lower sexual dimorphism is also lower Humans and Sexual Selection Humans are a strange case in sexual selection as the traits that have been sexually selected for in humans are very different than those in other apes Some prominent traits in humans associated with sexual selection On average males are 15 20 larger than females males and females have the same size of canines whereas in most apes the males have huge canines for competition human females are the only primates with permanently swollen breasts humans take this as a sign of fertility however in other primates females breasts are only swollen when they are nursing signaling that they are unable to get pregnant at that time in other primates females show swellings that indicate ovulation and fertility yet human females hide their ovulation and fertility in most animals the physical appearance of males is most important in competition and females are generally bland and uninteresting looking in comparison However in humans there is more emphasis on the physical appearance of females suggesting female to female competition over males as well as male competition for females
View Full Document
Unlocking...