字幕表 動画を再生する 英語字幕をプリント 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, Audible.com 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 Audible.com/Veritasium. 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.