Till Death Do Us Part Rachel Floersch and Kayla Bilderback

True Monogamy ●  Monogamy will evolve as a strategy

for all members of a community if it’s in the best interest of both males and females

●  Monogamy will be stable only when members of loyal partnerships have more surviving children than fickle creatures

●  Examples: Black Vultures, Chinstrap Penguins, Kirk’s dik-diks, California Mouse

“True monogamy is rare. So rare that it is the most

deviant behaviors in biology.”

Good Wife Theory Females cannot raise offspring alone.

“Female plot forced on males” - the females won’t cheat

because they don’t want to lose the help with the kids.

●  Not always accurate: ○  sexual fidelity can be in the males interest ○  female’s need for male help does not

necessarily guarantee her fidelity

○  Not all species males help raise kids (dik-diks)

Example: Fat-Tailed Dwarf Lemur

●  Males and females live together in pairs ●  Male “baby-sits” while female rests or gets food ●  But genetic testing has shown infidelity is common

So let’s look at some more plausible theories!

Danger Theory of Monogamy ●  Females are hard to come by, so the male

needs to take what he can get ●  Finding another female might entail a long or

dangerous journey ●  “The greater the risk, the greater the incentive to

remain” ●  Examples: Mantis Shrimp

○  Shrimp meet as adolescents and make burrow with mucus

○  Adults lose ability to produce mucus, can’t leave even if they wanted to

Pop-Em-Out Theory of Monogamy

If female has a short brooding time, the female might be ready to breed again before the male would find another mate anyway.

Example: Djungarian Hamster ●  Females live far apart from each other ●  A single female can produce 18 litters a year

○  1-9 pups per litter = up to 162 pups a year!

Sociopath Theory of Monogamy ●  Monogamy arises as a side effect of

aggression ●  Aggressive towards any animal that is not

their partner/ members of their own sex ●  Very Jealous ●  Example: Banded Shrimp

○  Live in pairs, they feed each other and stand guard for each other while molting

○  Fight shrimp of own kind to the death

Mutually Assured Destruction Theory of Monogamy Cheating or desertion by either partner results in total reproductive failure for both.

Example: Hornbills ●  All 45 species ●  Males and females completely co-

dependent

●  Nest hole sealed entrance with hole for female’s beak only, she molts flight feathers

●  Male feeds her, and once chicks hatch, he feeds the whole family

Theory of Genetic Predisposition to Monogamy ●  There could be a genetic predisposition ●  Hard to test because it’s difficult to

pinpoint (Genes code for a lot) ●  Example: Prairie Vole

○  Sex releases vasopressin which alters behavior ■  Makes males more aggressive after sex

“Consummate by

copulating anywhere

from 15- 30 times in 24

hours”

Humans...

●  As a whole, on the monogamous end of the spectrum ●  Relatively little physical differences - same size mates usually monogamous ●  Medium to small testicles = low to moderate risk of sperm competition

“Perhaps it will turn out, for example, that men with large testicles are prone to

seducing other men’s wives and have difficulty forming lasting bonds whereas men

with small testicles are prone to sexual fidelity and jealousy and turn all lovey-dovey

after sex.”

Activity: Groups of 3 Good Wife Theory of Monogamy

Danger Theory of Monogamy

Pop-Em-Out Theory of Monogamy

Sociopath Theory of Monogamy

Mutually Assured Destruction Theory of Monogamy

Theory of Genetic Predisposition to Monogamy