Sex & Sexuality In Evolutionary Perspective Flashcards
What is Biological Sex?
Binary categories based on biological differences
-chromosomal differences
- primary sexual characteristics
>reproductive anatomy
> the capacity for successful reproduction
Primary Sexual Characteristics
Reproductive Anantomy, i.e. the necessary structure for mammalian reproduction
-Puberty and Sexal Maturation
Secondary Sexual Characteristics
-Breast size, body size, body hair
- average height, weight
-strength endurance
*associated with but not required for successful reproduction
Fausto-Sterling: Five Chromosal Sexes
*XX: Female
*XY: Male
-XXY (Klinefleter Syndrome)
-XYY (XYY Syndrome
*XXX (Metafemale)
Intersexuality
> Mixed/Atypical Gonas and Gentalia
Significance of Biological Sex
> Clinical: fertility issues, bone density, metabolic issues
> Evolutionary: sexual selection, fitness (i.e. reproductive success)
Human sex and sexuality are BIMODAL but NOT BINARY
* no evidence that biological sex predicts gender identity, gender expression, or sexuality
Sexual Selection
*Subcategory of Darwinian natural selection
-Selection for specific traits that increase an individual’s reproductive success, even at a cost to survival
Trivers Parental Investment Hypothesis
> The sex investing the least in offspring (usually males) are expected to compete the most for access to mates
The sex invested the most in offspring (usually females) can afford to be choosy
Trivers Parental Investment Hypothesis: Females
> Females: Limited in # of offspring by resources necessary to gestate and raise infants & juveniles
-Polyandrous mating (with multiple males): confuse paternity, facilitate sperm competition
- Compete with other females to maximize the success of offspring
Trivers Parental Investment Hypothesis: Males
> Males: Limited in # of offspring by access to reproductively viable females
-Compete with other males for access to females, be more attractive than male competitors
-Try to mate with multiple females and maximize number of offspring
-Provide varying investment and support to genetically related offspring
Accurate Sexual Selection Theory
Mate competition and mating strategies differ by sex, as do competitive strategies and sexually-attractive traits in the opposite sex.
Zahavi’s Honest Signal Hypothesis
> Sexually attractive features in males= “honest” indicators of health and phenotypic quality because only healthy individuals can afford the energetic costs
-strong immune system (fend off infection)
- consistently adequate diet( vitamins, proteins, minerals)
Confers a selective advantage: more likely to produce offspring with genes for healthy immune system, hunting instincts, speed, endurance, etc.
Elements of Attraction: Secondary Sexual Characteristics
-Features that signal a competitive advantage
A. Large body size
B. Physical strength/ speed
C. Large teeth and/or claws
-Features that signal virility (usually in males) to potential mates
A. Bright coloring
B. Exaggerated tails, plumage
Risk of Runaway Selection
> *Male traits and female preferences become associated
Females choose males with more pronounced traits
-pass trait onto male offspring
-pass preference onto female offspring
constrained by natural selection
Reliable Indicator Hypothesis
-Female intrasexual competition –> sexual selection for prominent swellings: advertises sexual receptivity & peak fertility
- however not everything attractive is an indicator
Ex: breasts; under selective pressures related to lactation, not attractiveness (which is a cultural variable)
