Sex with Neanderthals?!

Neanderthal 

Recent genetic analysis shows that at least two other extinct species of human, the Neanderthal and the Denisovans  contributed to the DNA of people living today, suggesting that modern humans did in fact interbreed with other archaic humans. It seems as though Neanderthals and Denisovans, found predominantly in Europe and Asia interbred with modern humans, mixing our genes up together. Some of these modern humans with the newly acquired genes then brought them back to Africa about 10,000 years ago, giving modern humans global immunity to a lot of diseases. 

Peter Parham
Stanford University 

The research 

The team focused their analysis on Human Leukocyte Antigen genes, or HLA genes for short. HLA genes evolve quickly and play an important role for our immune system, which helps us to fight disease. Peter and the team studied the genomes of Neanderthals and Denisovans and compared them with the modern human genome from different populations. From this they managed to paint a picture of our past.
He explained, during an interview with discovery news that a small group of modern humans, left Africa and colonized other continents. This small group would have had limited HLA diversity and suffered the consequences through infections from diseases they hadn't been exposed to before. 
Interbreeding with the archaic humans local to their newly discovered continent, introduced new HLA variants into the modern human population, which helped to increase genetic viability and ability to resist infection. 

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Two sapiens and a Neanderthal!

Homo Sapiens Neanderthalensis 

I once believed that humans today evolved from the neanderthal.We didn't - the neanderthal lived alongside modern humans instead, sharing a common ancestor, the Homo erectus.  This means the neanderthal is more of a brother as opposed to a father. The Neanderthal is now classified as the Homo sapiens neanderthalensis, whilst the modern human is classified as Homo sapiens sapiens. Meaning that we are now considered part of the same species.

What does it mean to be a 'modern' human?                             

The term modern human, means ‘anatomically modern’, as in people that look like we do today. All other forms of extinct human, don’t look exactly like us, and are known as the ‘archaic’.The oldest fossil of a modern human, found in Africa dates back to 196,000 years before present, this means ‘we’ the Homo sapiens sapiens are estimated to be 200,000 years old.

Human Skull (left), Neanderthal Skull (right) comparison

Anatomically modern humans are mostly distinguished from the archaic humans by the physical features of the skull. As you can see from the diagram, the Neanderthal had a tough, robust skeleton, with much harder bones. A layer of bone also protrudes from above the eye socket, they have a smaller chin and their forehead is slanted backwards. If you look at the back of the skull, they have a pointy edge known as an ‘occipital bun’. These are all features that the modern man lacks for various evolutionary reasons.

Hi! :D

For example, anthropologists believe that the reason the Neanderthal had stronger bones was because they lived a more physically demanding life, whilst we became increasingly dependent on technology. Causing our bones to become weaker, however, it may be this same dependence on technology that has allowed us to outlive the Neanderthal and other archaic humans.

With the archaic humans extinct, our closest living relative is now the ‘chimpanzee’, who shares 98% of the modern human genome. 

Multiregional or Replacement?

There are two main models which attempt to explain the emergence of the modern human, how they colonised the world and outlived the archaic humans. These are the multiregional model and the replacement model.

Homo erectus 

The Multiregional Model

The multiregional model suggests that Homo sapiens didn't evolve at a specific time or place, instead they slowly evolved from Homo erectus (right) an ancestor of the modern human, that lived between 800,000 and 1.8million years ago, all over the world. Because they lived all over the world, gene flow between the geographical regions would have been constant. The multiregional model also suggests that interbreeding occurred between the Homo erectus and different types of archaic humans. And eventually, over many hundred thousands of years, all over the world, the Homo erectus became the modern human.

But how can this be possible? The earth is a large place, the chances that several different populations from several parts of the world, evolved in ‘exactly’ the same way at ‘exactly’ the same time is about as close to impossible as you can get. This unlikely type of evolution is known as ‘convergent evolution’, one of the main reasons the multiregional model is opposed by the replacement model.

The Replacement Model

The replacement model agrees that the Homo sapiens evolved from the Homo erectus, however, the replacement model believes that some populations of Homo erectus, migrated out of Africa and spread throughout the world. Those that migrated out evolved in a different way to those that stayed behind in Africa. The Homo erectus that stayed behind in Africa evolved into the modern humans, the Homo erectus in Europe evolved into the Neanderthals and the Homo erectus in Asia evolved into Denisovans. Another migration then occurred around 50,000 years ago, where the modern humans from Africa spread to Asia and Europe, replacing the archaic humans there, without interbreeding. The replacement model believes that at some point modern humans, Neanderthals and Denisovans cohabited in some parts of the world.

Although the replacement model is the leading and most widely accepted theory of the origin of the modern human, more recent genetic evidence shows that modern humans DID in fact interbreed with the European Neanderthal and the Asian Denisovans. So which is it?

Finding Eve: The Cartoon

Mitochondrial Eve?!

Whilst doing some research for my dissertation piece, I stumbled upon a very interesting topic about a woman; mitochondrial Eve.
According to the experts in human evolutionary genetics, Mitochondrial eve is the matrilineal, most recent common ancestor of modern humans! To you and me, this simply means that Mitochondrial Eve is our great, great, great, greatest, even greater than that, grandmother.

So how did the experts figure this out? Mitochondrial DNA is passed from mother to offspring without recombination, so therefore, all mitochondrial DNA in every living person is exactly identical to their mother's, and her mother's mother, and so on. So therefore we can use mitochondrial DNA to trace back the earliest of modern humans. Mitochondrial Eve is estimated to have lived around 160,000 to 200,000 years ago, in East Africa. Unlike the Biblical Eve, Mitochondrial eve was not the first and only woman alive during her time, however, her offspring are the only ones who made it into modern humanity, meaning the offspring of the other women of her time died off at some point. e.g. by only having male offspring that could not pass on the genetic information, or by dying through natural causes before reproducing. Times were tough back then. (I imagine). It was the discovery of mitochondrial Eve that made the hypothesis that modern humans originated recently from Africa and then spread from Africa to the rest of the world, replacing the archaic human populations that existed at the time, such as the neanderthals, the predominant and leading theory supporting our origin.

Y - Chromosomal AdamMitochondrial Eve is not our only most recent common ancestor! Meet Y-Chromosomal Adam. The Y chromosome is another part of the genome that is not shuffled about by evolutionary mechanisms in order to generate diversity. This means that the male Y chromosome is passed on in tact, so therefore Y chromosomal Adam is our great, great, most greatest, even greater than that grandfather. Y-chromosomal Adam is estimated to have lived also in Africa but at a different time to Eve, 140,000 years ago. Using mitochondrial DNA analysis we can look back on the genetic ancestry of the modern human like never before.

In my next post, I will be explaining the four main thoeries which try to explain the origin of the modern human.