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  • What are evolutionarily stable strategies?

  • >> In many cases it is kind of clear what is the best thing for an individual to do,

  • the best thing it can do to increase its survival with deduction.

  • But there are times when what is the best thing to do depends on what other individuals

  • in the population are doing, what, in particular, the majority of individuals in the population

  • are doing.

  • A hypothetical example we could call fishers and pirates.

  • And I am talking now about some kind of birds where there are two ways of getting fish.

  • These are sea birds.

  • Either you can fish for fish.

  • You either dive in a sea of catfish or you hang about waiting for a bird that has caught

  • a fish and steal it.

  • Those are pirates.

  • And these are two ways of making a living.

  • Now what is the best thing to be?

  • A fisher or a pirate?

  • And the answer is that it is not obvious, because it depends on what the rest of the

  • population are doing.

  • If the whole population is fishing then it could very well be that an individual could

  • mutate and become a pirate, because there are plenty of fishing going on.

  • And it is easy to steal a fish.

  • So then you might say: Well, natural selection then favors piracy, the gene for being a pirate

  • spreads through the population.

  • In a few generations now everybody is a pirate.

  • And there is no fish.

  • So piracy is not stable.

  • It is an unstable... it is evolutionary unstable.

  • Fishing might also be unstable, because if the whole population is fishing then a mutant

  • pirate invades, so a stable strategy is a strategy such that when all the population

  • is doing it no mutant individual could arise which would do better.

  • So neither fisher nor pirate in my hypothetical sort of game is evolutionarily stable.

  • What might be evolutionarily stable is some kind of ratio.

  • It might be 80 percent fishers and 20 percent pirates, something of that sort.

  • And the definition of stability in this case is when they are doing equally well.

  • A well known example is the sex ratio where any departure from the stable sex ratio is

  • penalized by natural selection.

  • If there are too many males an individual is better off having daughters.

  • And if there are too many females in a population an individual is better off having sons.

  • And so the stable ratio is 50-50, or, strictly speaking, it is 50 percent investment, economic

  • investment in sons and economic investment in daughters.

  • So an evolutionarily stable strategy is a strategy which cannot be bettered by any other

  • strategy provided that everybody else in the population is doing it.

  • >> You know, two years ago when this channel reached half a million subscribers, you guys

  • asked me who would I like to meet.

  • And I answered: Bill Nye, Neil DeGrasse Tyson, Richard Dawkins.

  • And since then, Bill Nye has taught me how to tie a bow tie.

  • I got to interview Richard Dawkins and on August 22nd and 23rd I will be hosting Neil

  • DeGrasse Tyson in Sydney and Canberra.

  • Link in the description.

  • And I really want to thank you guys, because I think it is your support that has made this

  • all happen.

  • You know, this video was animated by the Lyosax who is a viewer, but also runs his own channel.

  • So you should check it out if you like those animations.

  • Plus, has been the long term sponsor of this channel and what I love is that they

  • are sharing information just like I like to.

  • You know, this week it makes sense to share a Richard Dawkins book.

  • My favorite is The Selfish Gene, because it is not about a gene for selfishness.

  • It is about how genes themselves behave in selfish ways.

  • And sometimes that means the organism that contains those genes behaves in strange ways,

  • ways you might not imagine.

  • And that was a real consciousness raiser for me.

  • So you should definitely check out this book if you haven’t read it already.

  • You can actually download it for free, read by Richard Dawkins, by going to

  • Or you can pick any other book of your choosing for a one month free trial.

  • Audible is an awesome audio book website with over hundreds of thousands of titles in all

  • areas of literature including fiction, no fiction and periodicals.

  • So really you should check them out if you are at all into audio books.

  • Most of all I want to say thank you to you for making it possible for me to meet my idols.

What are evolutionarily stable strategies?


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進化穩定的策略英尺。理查德-道金斯 (Evolutionarily Stable Strategies ft. Richard Dawkins)

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    林宜悉 發佈於 2021 年 01 月 14 日