My DNA: Where Did My Ancestors Come From? (Part 2)

Prof. Dr. Reinhard Renneberg uses his own DNA as an example to show which migratory routes his earliest ancestors took.

The Great Migration

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The Y chromosome is passed on directly from father to son. It remains unchanged from generation to generation. However, it only remains unchanged if no mutation is involved, that is, a random, naturally occurring and usually harmless change. The mutation or the marker acts as a signal; it can be traced over generations as it is passed on from the man in whom it occurred to his sons, their sons and every other male family member over thousands of years.

In some cases, multiple mutations occur which then distinguish a particular branch of the family tree. As a result, each of these markers can be used to identify a specific haplogroup, as any individual carrying one of these markers will inevitably also have the other markers. They are therefore coupled together.

When geneticists identify such markers, they also try to find out when and in which geographical region of the world they first appeared. Essentially, each marker represents the beginning of a new lineage in the family tree of humankind. By tracing these lineages, we can get an idea about how small tribes of modern humans in Africa diverged and spread around the world tens of thousands of years ago. 

A haplogroup is defined by a set of markers; it includes all males carrying the same random mutations. These markers can be used to trace the migratory movements of our ancestors. One of the goals of the five year long Genographic Project was to create a large enough database of anthropological genetic data to answer questions about some burning questions about ancestral migration. 

Here's what we know so far: M168 – the earliest ancestor

Both skeletal remains and archaeological evidence suggest that the anatomically modern man evolved in Africa about 200,000 years ago and then set out from there to colonise the rest of the world about 60,000 years ago. 

"The man linked to the first genetic marker of your lineage probably lived about 31,000 to 79,000 years ago in northeast Africa in the area of the East African Rift Valley, possibly in what is known today as Ethiopia, Kenya or Tanzania. Scientists consider a range of around 50,000 years ago to be the most likely."

- Excerpt of the email from the Genographic Institute to me

His descendants formed the only lineage to survive outside Africa, making him the progenitor of all non-Africans living today. 

Why the dangerous migration? The Sahara turned green!

But why did humans for the first time venture out of the African hunting grounds they knew into unexplored dangerous land? 

It is likely that changes in climate triggered emigration from Africa. The African Ice Age was characterised more by drought than cold. About 50,000 years ago, the ice sheet of northern Europe began to melt, leading to a period of warmer temperatures and a more humid climate in Africa. This made parts of the hostile Sahara habitable and lush for a short time. 

"When the previously arid desert transformed into savannah, the animals hunted by your ancestors expanded their range and began to migrate through the emerging green corridor of grassland. Your nomadic ancestors followed the favourable weather and the animals they hunted. The exact routes have yet to be determined. In addition to the favourable climate changes, a great evolutionary leap in the intellectual abilities of modern humans occurred at the same time." 

YAP: An ancient mutation, Alu

Present-day sub-Saharan populations are characterised by one of three different Y chromosome lineages in the human family tree. Their paternal lineage E3b is one of these three ancient lines and is referred to by geneticists as YAP. 

YAP originated in northeastern Africa and is the most common of the three ancient genetic lineages in sub-Saharan Africa. It is characterised by a rare mutation known as an Alu insertion. Here, during cell division, a 300 nucleotide large fragment of DNA is inserted into different areas of the human genome. 

In my distant ancestor, the man who lived about 50,000 years ago, this fragment was inserted into his Y chromosome and he passed it on to his descendants. Over time, this lineage split into two separate groups. One is found mainly in Africa and the Mediterranean region and is called haplogroup E. The other, haplogroup D, is found in Asia and is characterised by the M174 mutation. 

"Your own genetic ancestry is within the group that stayed close to the place of origin. The feature bearers probably played a significant role in the culture and migrations within Africa at that time."

M96: Emigration from Africa 

The next important man in my lineage was born about 30,000 to 40,000 years ago in north-eastern Africa. With him came the marker M96. Its origin is not yet understood; perhaps further data can shed light on the exact origin of this lineage. 

"You are descended from an ancient African lineage that decided to migrate north to the Middle East." 

My relatives may have joined the Middle Eastern clan (with marker M89) when they followed the herds of large mammals northwards through the grasslands and savannahs of the Sahara corridor. However, a group of my ancestors may also have made this migration alone at a later time, following the route of the previously migrated Middle Eastern clan. 

Leaving closed doors behind

About 40,000 years ago, the climate began to change again, turning colder and more arid. Africa was hit by drought and the grasslands once again reverted to desert. For the following 20,000 years, the Sahara corridor was “closed” in a sense. The insurmountable nature of the desert left my ancestors with only two options: to remain in the Middle East or to continue migrating. Retreating to the home continent was no longer a possibility. 

M35: Neolithic farmers 

"The last common ancestor in your haplogroup, the man who developed the marker M35, was born in the Middle East about 20,000 years ago. His descendants were among the first farmers and helped spread agriculture from the Middle East to the Mediterranean region." 

By the end of the last ice age about 10,000 years ago, the climate changed yet again and became more favourable for farming. This probably helped to set the stage for the Neolithic Revolution. At that point, the human way of life changed from nomadic hunter-gatherers to sedentary farmers. 

Early agricultural achievements in the fertile crescent of the Middle East led to strong population growth around 8,000 years ago and encouraged migrations of peoples to large parts of the Mediterranean region. Their impact on the food supply represents an important turning point for humankind. Instead of living in small groups of 30 to 50 individuals, who were extremely mobile and loosely organised, farming brought about the first trappings of civilisation. 

Occupying a single territory required more complex social organisation and a shift from kinship ties within a small clan to more sophisticated relationships in a larger community. This stimulated the development of trade, writing, a calendar and paved the way for modern sedentary communities and towns. 

"These early farmers, your ancestors, dear Professor Renneberg, brought the Neolithic Revolution to the Mediterranean!"

  1. Renneberg, Reinhard et al. (2022, in Vorbereitung): Biotechnologie für Einsteiger (6. Auflage), Springer Spektrum, Heidelberg.