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  • Ever wonder why we like...do things for each other?

  • Like why we help our friends move even though we hate doing it?

  • And, for that matter, why a bee will sacrifice its life by stinging an intruder to protect the hive?

  • Why would a vampire bat regurgitate blood into the mouth of another bat that hasn't eaten that day?

  • Why?! That's a very nice vampire bat...I guess.

  • Eugh!

  • That's gross in like so many ways.

  • It turns out that this is actually a pretty big question.

  • Things like this have been stumping scientists for years.

  • Charles Darwin thought that altruistic behavior

  • was a potentially deal-breaking flaw for his theory of natural selection.

  • If the game was survival of the fittest,

  • natural selection couldn't possibly favor a behavior that made us less likely to survive.

  • Or could it?

  • Darwin studied beehives and realized that since sterile worker bees were helping their blood relatives,

  • especially the queen,

  • natural selection might favor altruism within related groups.

  • A hundred years later, in 1964, a British scientist named William Hamilton

  • actually came up with an equation to explain this.

  • He figured altruism could evolve as a trait if:

  • genetic relatedness, times the benefit of the action, was greater than the cost of the individual.

  • In other words:

  • since some behavior is hereditary

  • the genes responsible for altruistic behavior

  • could evolve if it's benefit exceeded whatever cost it had for the individual

  • because it helped the individual's relatives enough to make it worthwhile.

  • Hamilton called this idea "Inclusive Fitness"

  • expanding Darwin's definition of fitness

  • basically how many babies someone is making

  • to include offspring of other relatives.

  • Hamilton's ideas were a humongous hit with other scientists

  • because for starters it explains stuff like ant colonies.

  • Ants have virtually no personal lives,

  • everything they do, they do for the good of the colony.

  • And worker ants share three quarters of their genes.

  • They're actually more closely related to their sister ants

  • than they would be to their offspring.

  • So, according to Hamilton's equation, each individual ant has an exceptionally large genetic stake

  • in the survival of the colony

  • But Hamilton's ideas do not explain why some animals help others that they're not even related to.

  • Take humans, for example. We are deeply social animals, also exceptionally altruistic.

  • In fact, a lot of scientists think that humans evolved our huge, super smart brains in response to the

  • overwhelming benefits of engaging in selfless behavior.

  • Because it turns out sharing and cooperating are very mentally taxing.

  • Seriously, ask any three-year-old.

  • But if you think about it, you can see how we evolved to be altruistic for really self-serving reasons.

  • Like helping a friend move totally sucks, but you do it because you can conceive of a time in the future when that friend will help you move.

  • Or when that friend will drive out into the country to help you change a flat tire, or whatever.

  • Same with the bats, barfing some blood into your neighbour insures that someday, if you don't get something to eat,

  • somebody will come and vomit blood into your mouth,

  • and they'll expect the same from you in return, and so on, and so on.

  • Hamilton's equation does not explain that behavior, which complicates things, because equations are nice and comforting to have,

  • if you're a scientist. But if you can cooperate with others and resist the urge to horde resources,

  • knowing you'll be rewarded later, you'll be acting a lot like ants, bees and vampire bats.

  • Which makes me just feel all warm and snuggly all over.

  • Thanks for watching this episode of SciShow. I hope you have friends good enough to vomit blood in your mouth when you need it.

  • If you have any questions, comments, or ideas please connect with us on Facebook or Twitter,

  • or in the YouTube comments below, and if you want to keep getting smart with us here at youtube.com/SciShow,

  • head on over and subscribe, and we'll see you next time. Goodbye.

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B1 hamilton behavior altruism natural selection darwin blood

Altruism

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    ka ka posted on 2020/04/17
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