That proved to be true when the genomes were... of some non-vertebrates... were cloned, no such genes were found there, so I think it's now generally accepted that the adaptive immune system arose in one step or arose late in the evolution of the animal phyla, and the question then was at which stage, and the data on the MHC indicated that it would be with the origin of the jawed vertebrates. So when jaw arose, that presumably this form of immune system also emerged. Why it was so late, why... what was the stimulus for the origin, why other animals can do well without antibodies and without MHC and T-cell receptors remains an open question that still awaits... that somebody finds a way of answering it. One can speculate now about many possibilities but there are no hard facts to use to decide between the various possibilities.

But the MHC would lead us not only into the evolution of the MHC itself but also into the evolution in general, and as I said before, one of the question was how the species arise?  Why did we come to that question? Well, of course it was because it interested me and... interested me in general, but a direct lead was the following. When we found that the polymorphism is trans-specific, that a number of different forms of genes or alleles had to be transferred from ancestral species into the daughter species, then it occurred to me that this fact could be used to determine... to say something about the size of the founding population of the species. The very widespread belief, especially among lay people, but also among scientists and also among evolutionary biologists is that species arise from very limited number of founding individuals.  That... in the case of birds for instance they are... there is a couple of birds that strays off into a remote island and from this couple then arise a population which, because of its isolation from the original population begins to diversify and begins to evolve in a totally different direction and ultimately they are so different that they no longer could breed with the other... the original species if they would come together.  So there would be only a couple or a few individuals from when a new species would arise. That seemed to me to be, let's say not supported by the observation of the trans-species polymorphism but a direct study was needed to show that this is indeed the case, and we carried out such studies on three different models. One was human, the other was birds, and the third model was fish. So let's talk first about the humans.