Sexual Reproduction and Monogamy

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Sexual Reproduction and Monogamy
from The Myth of Monogamy by Barash and Lipton
(2001)
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CB 13.5
Evolution A species genetic component changes
as the individuals reproduce. These changes are
based on how the DNA changes and who reproduces.
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haploid
X 23 in humans
X 23 in humans
diploid
X 23 in humans
Sexual Reproduction The combination of genes
inherited from Mom and Dad.
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Asexual Reproduction
Sexual Reproduction
vs.
extremely low genetic diversity
greater genetic diversity
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Asexual Reproduction
genetically identical to parent
(this tree can reproduce both sexually and
asexually)
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Why does sexual reproduction exist?

• Cons
• Need two individuals
• Hard to find mate
• Diseases/Competition

• Pros
• Genetic diversity

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Screw worm flies
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F
M
sterile
Sterile male screw worm flies led to decreased
populations because of screw worm monogamy.
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F
M
sterile
In most other species, because females mate with
multiple males, introduction of sterile males has
little effect.
Sterile male screw worm flies led to decreased
populations because of screw worm monogamy.
F
M
sterile
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In most other species, because females mate with
multiple males, introduction of sterile males has
little effect.
Hi, want to study biology together?
F
F
M
M
sterile
fertile
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10-40 of offspring in monogamous bird species
are fathered by an extra-pair male
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• Social Monogamy pair lives/works together, but
  not faithful
• Sexual Monogamy pair raise young and only
  copulate with each other

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In mammals, child-rearing is most commonly done
by the female. She provides milk.
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Less than 0.01 of mammals are monogamous
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Do Males and Females have different attitudes
toward sex and relationships?
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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes

• Male answers
• Would you go out with me tonight?
• 50 yes

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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 6 yes

• Male answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 69 yes

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On a college campus an attractive male or female
asked the opposite sex I have been noticing
you around campus. I find you very attractive

• Female answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 6 yes
• Would you go to bed with me tonight?
• 0 yes

• Male answers
• Would you go out with me tonight?
• 50 yes
• Would you come to my apartment tonight?
• 69 yes
• Would you go to bed with me tonight?
• 75 yes

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Why do Males and Females have different attitudes
toward sex and relationships?
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The male perspective on monogamy
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Eggs require large resource input. A clutch of
bird eggs can be 20 of birds weight. Sperm
are cheap.
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Human Males 250,000,000 sperm/ ejaculation
Human Females 1 egg/month
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CB 46.15
The female reproductive system
CB 46.15
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Sperm competition

• Sperm can survive for several days in a womans
  reproductive tract.
• In Great Britain in a survey of 4,000 women
• 0.5 had sex with 2 different men within 30
  minutes
• 30 within 24 hours

sperm competition.
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CB 46.15
The female reproductive system
CB 46.15
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Female mammals provide additional resources in
form of milk.
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Mating pairs share genetic information and
possibly help in child-rearing
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What are the consequences of the different male
and female attitudes toward sex and relationships?
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Zebra Finch
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Zebra finch pairs were allowed to mate 9 times
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Then a new male was brought in and allowed to
mate with the female once.
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Last male advantage
Original male (mated 9 times) fathered 46 of
offspring
The last male that only mated once fathered 54
of offspring
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Last male advantage
To ensure fatherhood males mate guard and produce
copious quantities of sperm
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After successfully mating, male purple martins
call and attract younger males
Purple Martins
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The older males then cuckold the younger males
females
Younger males with nests near older males only
father 29 of eggs in their nests.
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Older males produce 4.1 offspring with their mate
and 3.6 by younger neighbors mate.
Younger males with nests near older males only
father 29 of eggs in their nests.
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Older males produce 4.1 offspring with their mate
and 3.6 by younger neighbors mate.
What advantage is their for females to accept or
solicit EPCs?
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Gunnisons Prairie Dogs
Sexually monogamous female squirrels have a 92
chance of successfully giving birth.
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Gunnisons Prairie Dogs
Sexually monogamous female squirrels have a 92
chance of successfully giving birth. Non-monogamo
us females have a 100 chance of giving birth
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Can females detect compatible genes?
http//www.pbs.org/wgbh/evolution/library/01/6/l_0
16_08.html
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How can a female know which male has successful
genes?
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Females may choose traits, like large displays,
that are disadvantageous for male survival.
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CB 51.36
How can females determine good males?
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CB 51.36
Color Bright coloring can be correlated with
health
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CB 51.36
But a male with a mate is judged as being high
quality even if he is less colorful
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How does evolution work for a behaviors such as
monogamy?
bye
monogamous
non-monogamous
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How does evolution work for a behaviors such as
monogamy?
bye
non-monogamous
monogamous
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How does evolution work for a behaviors such as
monogamy?
After several generations
monogamous
non-monogamous
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• Males must choose between having more offspring
  (more mates) or helping to raise fewer offspring
  (sperm do not require many resources)
• Females choose males that can provide good
  genes or resources for offspring
• (eggs, gestation, and/or lactation require high
  resource input)

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Am I the only one? Am I better off helping with
these kids or should I mate with someone else?
Is this the best I can do? Maybe I can find
someone with better genes or more genetic
diversity.