mean patterson i'm a mathematician by training but i've had multiple careers i've worked in cryptography for the u s and british government i worked in finance modeling financial markets and now i do genetics and it does look like three very different disciplines but all of them involve mathematical modeling of complicated data and that's what i think i've learnt a little bit about how to do you do l underlying disciplines to make sure what you're doing makes sense but the modeling definitely has things in common and some of the technical techniques i use map across directly i also think that you learn a skill set about is this model working on this data and  that's a kind of fuzzy question and i think i've been working technically for a very long time now and over the years york was fairly deep expertise in how you can answer that i have what i call my smell test which is does this data look right and that can be really quite useful but today we're going to talk about genetics and in particular using genetics to learn about human history so what happens in genetics as of course you know you get your genome your genetic material  from your mother and your father and the genetics the genome involves strings of of information in a fuller alphabet so for example humans have two chromosome threes which you can think of as strings of a c s g s and t is a for chemical and you get one of your chromosome three for your mother and one of ten generations you have a lot of ancestors and the genome is being contributed to by multiple ancestors that's just a little bit a background what happens is the genetic variation starts to differ between populations that aunt exchanging genetic material mating with each other so over thousands of years if two populations separate the genome start looking very very slightly different so for example it's quite easy to tell genetically if someone comes from west africa or comes from  europe you may make very very occasional mistakes because you may have an african immigrant into europe or something like that but by and large it's pretty easy to do that and we can do much subtle of things if you tell me  his half a dozen people and they're either english or italian make a guess i will get that right nearly every time because there's just enough separation between the history of a ten years ago with some success using modern human d n a but now there's been a massive technology shift it's now possible to recover genetic material from ancient bombs and this changes everything because instead of having to try and use mathematically what the  ancient material must look like we can now go and look directly it's much much easier so let me say a little bit about what's not technically possible you take an ancient fassel and you try and recover d n a from that actually even with the best modern methods more than half the time you fail the d n i degrades in the ground by other bad things happen bugs eat it up and there's not a low certainty of tom that will actually get useful material but some of the time we do and it can be very very old one of the first major successes which i was involved with working with a group in germany was recovering a d n a sequence of a neanderthal who died in siberia more than forty thousand years ago and the d n a we recovered was of the same quality as i would get from taking a blood sample from you and running it out in a edge is d n a recovered from the material in spain from about four hundred fifty thousand years ago the d n a is not very good quality but we got a reasonable amount and the were absolutely ideal so that's some technical background about what we can do what kind of materials do we need to extract d n a from bones but we actually live quite a last couple of years for a bone called the petrus bone which is involved in the ear behind here and this is very very hard and it seems that it's so hard that the bacteria are not able to get in so we've had fantastic success with these particular bones of the skull and that's been another technical advance which is greatly improved the probability that we actually successfully get material so i am my coworkers are really interested in all of human history and we are interested in collecting ancient material really from anywhere in the real from asia all over asia agent iran and especially in europe the density of material in europe is much higher  elsewhere simply because the archeologists have been working harder in europe than elsewhere on the planet so we've been looking looking especially at asian history in europe and let me tell you a little bit about that so my own opinion is that this ancient d n a work is less interesting  completely without point when we get nearer modern times and the historical societies are literate so they are writing the point is in a society which is writing there's typically of the history but if we go back further everything is much less clear so in europe we now have a really very interesting story and i'll take a few ministers tell you about that so  about eight thousand b c in europe at that time there are no farming going on in your there's farming going on in the middle east and the people living in europe are hunter gatherers so they are hunting animals big game and they are collecting vegetables and roots and we think the semi nomadic because you have to follow the animals and so on and the first discovery we made is that the genetics across europe remarkably homogeneous so you look at people from ancient spain eight thousand b c or in germany or hungary genetically they're really quite similar but if you go further east on to finland or the russians you see a big genetic shift and we're still thinking about exactly why that happened but these hunter gatherers do not look genetically a tall modern europeans the next thing that happens is farming arrived in europe and there's been a question for a long time about where the farming came in because the old hunter gatherers live and probably from the middle east how to do it or did new people come into europe and we now know the answer it's absolutely new people and the proof of that is you get from very early farmers in europe it's completely different from the hunter gatherers must be new people groups of people were all genetically very different from each other and it turns out the modern europeans are three way mix of those groups none of this material could remotely have been discovered  is we talked about these step people coming into europe and there was obviously a massive population replacement occurred how did that happen it's  unlikely to have happened simply by peaceful negotiation it till very recently i thought it was almost certainly violence step people are riding horses evenly useful  war and i think thought that they come in and horseback and the farmers can't really deal with that but this in fact another story which is to come maybe even more likely we're not sure yet we've discovered that on the step as early as three thousand b c the people there were carrying be panic play and we think that in europe there was no plague at that time a story trading starts between the step and the farmer's that's very likely and in fact there's archaeology suggesting that must have happened and the step traders bring their little friends with them when europeans show up in the americas the europeans that carry lots of diseases like smallpox and measles which is a complete killer if you have no resistance and it devastated still exploring but it's an interesting possibility and not volunteer in the same way as i originally thought a personal interest of mine is how indo european spread so linguists have divided up the languages of the world into very large families and the largest family both in numbers of people who speak it and the geographical spread is in the european and from the name you might guess correctly that this is spoken by most of the peoples of europe languages like french german english  a all in the european latin and greek as well but also in india hindi which is the majority language of north india is in the european and hindi to rives from ancient sanskrit which was being spoken in north india as early as fifteen hundred b c the spread geographically is even larger than you might know there's a fascinating group called the carians who were in western china about five hundred b c they were literate they wrote in chinese characters so we can read their texts and isn't in the european language so by five hundred b c we know for certain that there are people speaking the language group of the atlantic coast in europe and also in western china and also in north india very interesting and important question is how did that happen this question has been argued by archaeologists and linguistic theorists for nearly two hundred years but the d n a is now also giving evidence for the us we think that this step culture came into europe almost for certain  five hundred b c they were the first peoples in the world to use wheeled vehicles and probably they were also riding horses so at the moment we don't have any ancient d n a from india that we have wonderful collaboration's but india is a tough place to get d n a from because it's hot and wet and this is bad for the preservation of genetic material we do have d n a from ancient iran and that's fascinating and there's clearly a genetic relationship between ancient iran and modern india and i'm struggling to understand that in my own work so what do i actually want my day to actually look like well it at that point we have a computer file which consists of short four letters four little strings and what to do well because this is modern human sequences we don't expect to get an exact match but you would expect that there be only two or three differences in one hundred letters and that would uniquely place the similar or different to other modern human populations so how do we how do we date the material well the most common method is simply archaeological if you excavate a site very often we archaeologists are extremely confident which in favorable circumstances will actually allow us to date material to directly from the genetics it's very nice to do that because you get a cross check of material particularly for the very old material if it's thirty or forty thousand years old the archaeological methods become very difficult to apply and we now have some hope that we can do something with genetics new dialogue lee work on is recovering what's called three way mix of populations that's how do we know that well we first of all we see is genetic shifts and then there's ways of measuring how close a population is to another by two thousand b c e we see people in europe who clearly share a lot of genetic variation for the steps and we can model that mathematically and the only reasonable explanation must be there's been some genetic exchange mating between the european peoples and the step people's genetics is the area of biology which is most mathematical and there's an interesting reason for this it's that the basic processes of exchange of genetic material can be very simply described the how you get your i build mathematical models and so for instance if i have an ancient population at a modern population a natural question is do i believe that this modern population could be directly descended from the ancient one or has something else happened and we have formal mathematical tests for this many derive by other people in the community some of them worked out by me and so i take the d n a and apply this to us and maybe it tells me now this population is not ascended something else must have happened then we try and think how can we can we refine our models so for have a formal test for whether one population is directly descended from another and you take our data you run that test either side say no it can't be and then we have to build a more complicated model to try and explain what we're seeing in the data so in my day to day world i continually writing down mathematical models testing the data usually discovering the model is incorrect and then going back and trying again i do think that it's very important in this kind of work to try and do formal testing of your models requires some sort of mathematical knowledge it's worth remembering the model is just a model there's a famous quote statistics not for me that all models  wrong but some are useful and that's really the point here of course the true complexity is such that we could never hope to write it down actually it's very important to get a reasonable number of samples from population many of you will have heard of the famous ice man who was covered new years ago  glacier and the people who discovered him so this body of a glacier so there's been a murder and they were right but the murder took place in three thousand b c and region and he wasn't told typical of other people living there that now turns out not to be true we've now looked at the whole number of samples from three thousand b c alpine area and in fact he seems