Transcript Mating Systems

Mating Systems
Adapted from Dixon, A., Dixon, B., Anderson, M., 2005, p. 3
Presented by: Megan Dorrian
Stefanie Galich
Sean Ivester
Sexual Selection and the Evolution of
Visually Conspicuous Sexually Dimorphic
Traits in Male Monkeys, Apes, and Human
Beings

Quantitative approach
 Measured sexually dimorphic characters
 Compared development in monogamous,
polygynous, and mulitmale-mulitfemale mating
systems
Darwin’s Sexual Selection

Traits that improve reproductive success have
been selected during the course of evolution,
especially among males, primarily via
intrasexual selection
 Examples: sexual attractive adornments, antler,
horns, enlarged canine teeth and other
masculine weaponry
 Such features also provide info to females
regarding masculine reproductive condition
The Different Mating Systems





Monogamy: one male and one female form a durable
reproductive partnership, tend to have little sexual
dimorphism
Polygyny: some males mate with more than one female
Polyandry: some females mate with more than one
male
Multimale-Multifemale: males and females mate with
members of the opposite sex with no long-term bonds
Order of visual trait development among systems:

Polygyny > Monogamy > Multimale-multifemale
Non-Human Primates
 Exist
in polygynous and multimalemultifemale mating systems
 Primates have pronounced sex differences
in canine size and body size


Largest physical sex differences among males
Males of polygynous primate species tend to
be much larger than females
Apes

Mandrill:





Polygynous or multimale-multifemale mating system
Mate guarding of females
High sexual dimorphism illustrating extreme selection pressure
to signal rank to other males and their attractiveness to females
Alpha males suppresses secondary sexual development in
subordinate males
Orang-Utan:



Do not form groups
Extreme sexual dimorphism and adornments of males as a
result of competition for females
Alpha male suppresses secondary sexual development in
subordinate males
Humans

Primarily monogamous





Low sexual dimorphism and body weight.
Relatively high score for masculine visual traits
Canine teeth of all human beings are small, unlike the large
canines of polygynous monkeys and apes
Males have relatively small testes in relation to body weight
Two sexes are of similar size:
• Men are somewhat larger, stronger and more muscular than women
• Women have more body fat

Some polygynous, usually among men of higher social
status


Have higher ratings for masculine visual traits
Sexually dimorphic visual traits positively correlated with the
degree of sexual dimorphism in body weight mainly in
polygynous mating systems
Humans (continued…)

Men:


Taller men have greater reproductive success
Deep masculine tone voice, more muscular torso with broad
shoulders and narrow waist is more attractive by some women
• Mesomorphic (muscular) males are rated most attractive by women


Consistent with the theory that sexual selection has an effect on
visual signals advertising masculine strength, physical health,
age and underlying endocrine condition in the human male
Mesomorphy may be an indicator of superior cardiac function
and metabolic health
• May be favored because they offered females greater protection
and had physical advantages in hunting


Endomorphy (heavier built) has been correlated with greater risk
of heart disease and poor general health
Hair on the trunk and face is a sexual dimorphic character
• Do not know why have evolved
Women’s mean ratings for sexual
attractiveness based on somatotypes
Adapted from Dixon, A., Dixon, B., Anderson, M., 2005, p. 13
Peacocks

Females are directing
evolution through
choice of mates
 Male competition
 Sexual selection
theory


Healthy, fit, strong
peacocks have larger
tails
Evolution operating on
sexual selection
Natural Selection Tale
of the Peacock
MAIN POINTS

Overall complexity of masculine secondary
sexual traits are greatest in polygynous mating
systems
 Male human secondary sexual traits are
associated with monogamous mating systems
 Among anthropoids studied males had the
highest visibility of sexaully dimoprhic traits
compared to females
Critique
 Greatly
pointed out sexual dimorphism
among primates, monkeys and apes, but
needs more cross cultural studies to
determine the function of human dimorphic
traits
 There needs to be a strategy to
quantitatively measure the sexual
dimorphic visual traits. (i.e. hair, red skin)