By Sarah S.
Spencer Wells asks the question of how the human species got so diverse. He explains how they are using the tools of genetics, especially popular genetics, to tell us how we generated the diversity and how long it took.
At the start of the video, Wells says how different we are, "there is so much diversity around the globe. 6,000 different languages, spoken by six and a half billion people, all different colors, shapes, sizes." He asks how do we explain that diversity? He breaks that into sub questions, the first was about our origins, and the second if if we are all from one source, how are we all over the world? He says the question of origins was answered by Darwin, when he stated that our distant ancestry was from apes. Apes were from Africa, so that is where we are also from. But Wells is not asking about where we came from, but rather specifically about our human ancestry. He says if you go back billions of years, our DNA can connect us to every living thing on earth.
"The question of our origin is actually a question of our genealogy." Wells says they are trying to make a family tree for everybody alive right now. You make a family tree by starting with the present, you put you and your siblings, who share parents in common, and then to cousins who you share a grandparent with. And you continue on, gathering information on distant relatives until, what Wells says, you hit a brick wall, when you do not know anything else about your ancestors. He says this is history, and we, apparently, have no written record of it. But he says we do, in our DNA. DNA is our genetic code, it is the information for our bodies. Our genes are made up of DNA, and our genes are passed through generations. We copy our DNA molecules, so that they can be passed on, but sometimes there is a small change. Wells compares to copying out the longest book ever, 100 hundred times, by hand. Sometimes you will make a mistake, and this sometimes happens when the DNA is passed on through the generations. Wells says, "but when it does happen and these changes get transmitted down through the generations, they become markers of descent. If you share a marker with someone, it means you share an ancestor at some point in the past." By looking at that pattern, and assessing the age when this occurred, they have made a family tree for everybody alive today. There are two branches on the tree: one is the Mitochondrial DNA which traces the maternal line of the descent through the mothers, and the other is the Y chromosome which traces the paternal line for men. Everybody falls into one of those lines. The deepest lineage of the tree comes from Africa, so that means that the DNA "mistakes" have been accumulating there longer. So it is in our DNA that we originated from Africa.
60 000 years ago, we were still living in Africa, but around that time, the people started leaving Africa to populate the rest of the world. Wells asks "Why was it that we seem to have come out of Africa so recently?" He says the answer is in the weather. At that time, 60 000 years ago, we were in the worst part of the last ice age. There was massive ice sheets in the northern hemisphere, but in Africa, they were drying out. The sea levels were lowering, and Africa was turning into desert. 70 000 years ago, we were nearly extinct, there was only about 2000 individuals living. But then art came to life, and stone tools became finely crafted. Which gives evidence that humans learned how to hunt certain prey at certain times of the year. So then the population grew, and the social networks grew between 50, 60, 70 thousand years ago. Modern language was used to convey complex ideas, so we became more social. Humans reached the Middle East about 4500 years ago, and then Europe about 3500 years ago.
"It is a very coarse sketch of how we migrated around the planet. And it's based on a few thousand people we've sampled from, you know, a handful of populations around the world, studied a few genetic markers, and there are lots of gaps on this map. We've just connected the dots."
I think Spencer Wells had a good talk. He knew a lot about the subject, since he studies it. He used some diagrams and pictures, but I believe he could have used more. I am sure all the people that were with him while he made his talk, understood what he was saying more than I did, so maybe they did not need diagrams to follow along with, but I felt that would have helped me. He used big words, for a big subject, that his audience could follow along with.
Wells was very persuasive in telling us how we can use DNA to follow where we came from. He makes you believe what he is saying is all right, since it does sound very logical.
Overall, it was a good talk, and I enjoyed listening to what he had to say. He did make me want to learn more about our genes, and where we come from. It is a very complex topic, and he shortened it into a 20 minute talk, and I think if he used more and better diagrams and pictures it would have helped a lot.