3. Intersexual Selection
• “female-choice”
• Bateman’s Principle: the sex which
invests the most in producing offspring
becomes a limiting resource over which
the other sex will compete
5. Intrasexual Selection
• “Male-male competition”
• Strategies used to compete with
members of the same sex for access to
members of the opposite sex
• Female ornamentation produced at
expense of their offspring which makes
them lose fitness
7. Sexual Dimorphism
• Differences between individuals of
different sex of the same species
• Male is larger in most mammals
• In insects, spiders, birds, reptiles,
amphibians the female is usually larger
10. Coloration in Animals
Female Mandrill: facial coloration
proportional with age (signals
reproductive ability)
Three Spined Stickleback:
Females prefer males with
intense red coloration
(signals parasite resistance,
because parasites reduce
intensity)
12. Physical Attractiveness- Skin
• Skin color distribution influences perception of
female face
• Attractive signals correspond to high
Estrogen/Testosterone ratios
• Skin problems may signal a disturbance in E/T
ratio and reduced reproductive ability
14. Physical Attractiveness- Symmetry
• Phenotypic indicator of biological fitness
• Fluctuating Assymetries (FAs) result from
genetic and environmental stresses during
development
• Indicates developmental homeostasis
• Cue of high parasite resistance (parasite theory)
– Defense against parasites: genetic diversity
(dependent on individual heterozygosity)
– Heterozygosity related to symmetry of bilateral traits
15. Physical Attractiveness- Scent
• Androstenone- secondary sex characteristic
(men give off three times more than
women)
• Secondary sex characteristics correlated
with offspring survival
• During ovulation, female is most fertile
• Increase in sensitivity to androstenone
16. Relativity in Physical Attractiveness
• Female choice is modified by female’s viability
• Female three-spined sticklebacks in worse
condition show preference for less brightly colored
males
• In humans, relative height
• Humans adjust preferences to increase pool of
partners
• Women who considered themselves physically
attractive showed greater preference for symmetry
in male faces
18. References
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