Sexual Reproduction and Monogamy from “The Myth of Monogamy” by Barash and Lipton (2001)

Evolution: A species’ genetic component changes as the individuals reproduce. These changes are based on how the DNA changes and who reproduces. CB 13.5

haploid diploid X 23 in humans X 23 in humans X 23 in humans Sexual Reproduction = The combination of genes inherited from Mom and Dad.

extremely low genetic diversity greater genetic diversity vs. Asexual Reproduction Sexual Reproduction

Asexual Reproduction genetically identical to parent (this tree can reproduce both sexually and asexually)

Why does sexual reproduction exist? Cons: Need two individuals Hard to find mate Diseases/Competition Pros: Genetic diversity

Screw worm flies

Sterile male screw worm flies led to decreased populations because of screw worm monogamy. FM sterile

Sterile male screw worm flies led to decreased populations because of screw worm monogamy. In most other species, because females mate with multiple males, introduction of sterile males has little effect. F F M sterile M

In most other species, because females mate with multiple males, introduction of sterile males has little effect. FM sterilefertile F M Hi, want to study biology together?

10-40% of offspring in “monogamous” bird species are fathered by an extra-pair male

Social Monogamy = pair lives/works together, but not “faithful” Sexual Monogamy = pair raise young and only copulate with each other

In mammals, child-rearing is most commonly done by the female. She provides milk.

Less than 0.01% of mammals are monogamous

Do Males and Females have different attitudes toward sex and relationships?

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…” Male answers: …Would you go out with me tonight? = 50% yes Female answers: …Would you go out with me tonight? = 50% yes

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…” Male answers: …Would you go out with me tonight? = 50% yes …Would you come to my apartment tonight? = 69% yes Female answers: …Would you go out with me tonight? = 50% yes …Would you come to my apartment tonight? = 6% yes

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…” 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 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

Why do Males and Females have different attitudes toward sex and relationships?

The male perspective on monogamy

Eggs require large resource input. A clutch of bird eggs can be ~20% of bird’s weight. Sperm are cheap.

Human Females: ~1 egg/month Human Males: 250,000,000 sperm/ ejaculation

CB The female reproductive system CB 46.15

Sperm competition: Sperm can survive for several days in a woman’s 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.

CB The female reproductive system CB 46.15

Female mammals provide additional resources in form of milk.

Mating pairs share genetic information and possibly help in child-rearing

What are the consequences of the different male and female attitudes toward sex and relationships?

Zebra Finch

Zebra finch pairs were allowed to mate ~9 times

Then a new male was brought in and allowed to mate with the female once.

Original male (mated 9 times) fathered 46% of offspring The last male that only mated once fathered 54% of offspring Last male advantage

To ensure fatherhood males mate guard and produce copious quantities of sperm Last male advantage

Purple Martins After successfully mating, male purple martins call and attract younger males

The older males then cuckold the younger male’s females Younger males with nests near older males only father 29% of eggs in their nests.

Older males produce 4.1 offspring with their mate and 3.6 by younger neighbor’s mate. Younger males with nests near older males only father 29% of eggs in their nests.

Older males produce 4.1 offspring with their mate and 3.6 by younger neighbor’s mate. What advantage is their for females to accept or solicit EPCs?

Gunnison’s Prairie Dogs Sexually monogamous female squirrels have a 92% chance of successfully giving birth.

Gunnison’s Prairie Dogs Sexually monogamous female squirrels have a 92% chance of successfully giving birth. Non-monogamous females have a 100% chance of giving birth

Can females detect compatible genes?

How can a female know which male has successful genes?

Females may choose traits, like large displays, that are disadvantageous for male survival.

How can females determine “good” males? CB 51.36

Color: Bright coloring can be correlated with health… CB 51.36

But a male with a mate is judged as being high quality even if he is less colorful CB 51.36

bye How does evolution work for a behaviors such as monogamy? monogamous non-monogamous

bye How does evolution work for a behaviors such as monogamy? monogamous non-monogamous

How does evolution work for a behaviors such as monogamy? monogamous non-monogamous After several generations…

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)

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