Think of the AIDS virus. If the AIDS virus enters a person... a host, it's just one single virus particle, so before you can measure it in your five... six litres of blood you have in your body, that virus must multiply, multiply, multiply. A biblical verdict, multiply. And you can just detect the virus when it is about a billion particles in your blood. A billion particles is still an exceedingly low concentration. You know...
[Q] 10 to the what...?
... in a gram of water you have about 1024 molecules, that's the Avogadro number, so 109 is a very small number if you take your total blood content of the body. But what does it mean, a billion molecules? There is first only one molecule, and the next moment it duplicates, there are two, and the third moment you have two times two, that means four, then you have eight, you have sixteen, you have thirty-two, sixty-four, and before you get a billion you have to go through thirty such replication rounds, because 230 is just about 109. Which means that all the particles have on average accumulated thirty mistakes, thirty errors, because they have gone through thirty such replication rounds and in each round there is on average one. Of course what you truly have is a Poissonian distribution, which means if you are at your error threshold a third of your molecules has no error, a third has one error and another third has more than one error. That's about what you get at the threshold.
So he had the experimental proof for our quasispecies model. And that convinced us also that we have to do experiments in biology. You cannot just make theory, you have to find out is your theory... do you really find the effect which plays a role in nature. And this turns out to be a general law in nature. Evolution takes place just below the error threshold.
