Is human evolution speeding up or slowing down? - Laurence Hurst
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Much that we now know about human evolution and our past has come from the study of the DNA of people all over the world. We can also extract and study the DNA of individuals that are long dead. We can, for example, know about the DNA of our close relatives, Neanderthals and Denisovans, even though none are alive today. The Swedish geneticist Svante Pääbo led many of these efforts and is a key player in the very new field of paleogenetics.
We use DNA to infer genetic similarity between people. Just as identical twins share the same DNA and siblings share much of the same DNA but aren’t genetically identical. From patterns of similarity in DNA, we can know how closely related different humans are to each other and to other species. On an everyday basis, we can use this for paternity testing and forensics. We can also use sequence similarities to infer the movement of people across the globe. The DNA evidence suggests that the first humans most probably lived in Africa but since then sub-populations have moved all over the world, inhabiting all continents. Looking for rapid changes in the DNA in these sub-populations we aim to pinpoint the genetic changes that enable each population to live in their environment. The DNA also tells us that the cause of much selection in humans is infectious diseases and past epidemics.
We now know, also, that many humans alive today still have segments of Neanderthal DNA, most probably because of interbreeding. Genetic analysis has also revealed a direct descendent of two early human groups.
The same method of looking for similarity is also what tells us about older evolutionary history. We now know, for example, that the closest living relative of humans are chimpanzees and bonobos. We estimate that we shared a common ancestor with them about 6-7 million years ago.
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