Archaeogenetics facts for kids

Archaeogenetics is a cool science that mixes archaeology (the study of old human history) with genetics (the study of DNA and how traits are passed down). It's all about studying ancient DNA from things like old bones, seeds, or preserved tissues. This helps us learn about people, animals, and plants from long ago.

By looking at ancient DNA, scientists can figure out:

• How ancient groups of people moved around the world.
• When and how animals and plants became domesticated (like dogs from wolves, or corn from wild grasses).
• How living things have changed over time (their evolution).

The word "archaeogenetics" comes from the Greek word arkhaios, meaning "ancient," and "genetics," meaning "the study of what you inherit." An archaeologist named Colin Renfrew came up with the term.

In 2021, scientists made a big discovery. They successfully found and read the oldest DNA ever. It came from a mammoth that lived over a million years ago!

Early Discoveries in Genetics

Before archaeogenetics became a field, some scientists did important work on blood groups and genetics. Their discoveries helped set the stage for understanding how genetics could be used to study ancient populations.

Ludwik Hirszfeld (1884–1954)

Ludwik Hirszfeld was a Polish scientist who studied tiny living things (microbiology) and blood. He helped discover how blood groups are passed down in families. He also studied ABO blood groups.

In one study, he noticed that the amount of blood group A decreased from western Europe to India. Blood group B showed the opposite pattern. He thought this might be because different blood groups mixed through migration (people moving). His work showed how blood types could be used to track human populations.

Arthur Mourant (1904–1994)

Arthur Mourant was a British scientist who studied blood. He collected lots of information about how common different blood group genes were around the world. He helped create a "genetic map" of the world by studying blood groups in many different groups of people.

Mourant also found new blood group types. His work was very important for archaeogenetics. It showed that genetic information could help us understand how different groups of people are related. It also helped scientists test ideas about how populations change over time.

William Boyd (1903–1983)

William Boyd was an American scientist known for his research on the genetics of human groups in the 1950s. He found that certain plant proteins (called lectins) reacted differently to various blood types. This discovery led to finding thousands of plants with these proteins.

Boyd collected blood samples from all over the world. He found that blood groups are passed down and are not changed by the environment. In his book Genetics and the Races of Man (1950), he grouped the world's people into 13 different types based on their blood profiles. The study of blood groups is still a key way to learn about inherited traits linked to different human groups.

How Ancient DNA is Studied

Studying ancient DNA is tricky! Scientists need special ways to find, clean, and analyze these old genetic clues.

Finding and Keeping Fossil DNA Safe

Finding fossils often starts by looking at the type of rocks in an area. Or, scientists might spot bones on the ground. They can also use technology like special X-rays to find hidden fossils. Tools like knives, brushes, and small trowels help carefully remove fossils from the ground.

It's super important to avoid contaminating ancient DNA. Scientists wear gloves and store specimens in very cold freezers (-20°C) right after they are found. Labs that study ancient DNA often have separate air systems. This stops new DNA from mixing with the old samples.

Bones are ground into a powder. Then, they are treated with a special liquid before a process called PCR. Sometimes, preserved skin can also be used instead of bones.

DNA doesn't last forever. It breaks down and changes over time, especially because of bacteria and fungi in the soil. The best time to get DNA from a fossil is right after it's dug up. Fossils found in warmer places often have less DNA. Also, big changes to a fossil's environment, like being dug up, can harm the DNA. Things like washing, brushing, sunlight, and the soil's chemicals also affect how well DNA is preserved.

Getting DNA Out (Extraction)

Once a sample is collected, DNA needs to be taken out. A common method uses a material called silica. This method helps collect ancient DNA from bone samples.

Getting ancient DNA is hard because DNA breaks apart after an organism dies. This means ancient DNA strands are usually very short. Also, other DNA, like from bacteria, can be in the sample. Scientists take many steps to prevent this. For example, they use special labs with separate air systems. Fresh fossils are best because washing them carelessly can cause mold to grow.

The silica-based DNA extraction method is used to clean DNA from old bone pieces. This makes the DNA ready for PCR. Silica helps DNA stick to it, separating it from other things in the fossil that can stop PCR. But silica itself can also stop PCR, so it must be carefully removed later.

Here's how the silica method generally works:

• The bone is cleaned, and its outer layer is scraped off.
• A sample is taken from a strong part of the bone.
• The sample is ground into a fine powder and mixed with a solution to release the DNA.
• Silica solution is added, and the mix is spun to help DNA stick to the silica.
• The liquid is removed, and a new liquid is added to release the DNA from the silica.

This method is quick and doesn't need a fancy laboratory. It works at room temperature and can be used for different sample sizes. However, it only works for bone and teeth samples, not soft tissues. It's also less effective for fossils that have been treated (like for museums). And, like all DNA work, contamination is a big risk.

Polymerase chain reaction (PCR) is a process that makes many copies of a small piece of DNA. It's often used for ancient DNA because there's so little of it. PCR has three main steps:

• Denaturation: High heat splits the DNA into two single strands.
• Annealing: Short DNA pieces (primers) attach to the single strands.
• Extension: An enzyme (Taq polymerase) adds matching DNA building blocks to create two full double strands.

This process is repeated many times, making millions of DNA copies. For ancient DNA, it's repeated even more. One challenge is that ancient DNA is so short, so PCR needs special overlapping primers.

What Archaeogenetics Teaches Us

Archaeogenetics helps us understand the past of humans, animals, and plants in amazing ways.

Human History

Archaeogenetics has helped us learn about how humans spread across the world.

Africa

Scientists believe modern humans first appeared in Africa at least 200,000 years ago. Some evidence suggests it might be over 300,000 years ago. Studies of different types of DNA show that about 1,500 men and women were in the first group to leave Africa.

Genetic studies also support the idea that groups of Bantu-speaking people moved into Southern Africa about 5,000 years ago. DNA also shows that people from Sudan, who spoke Nilo-Saharan languages, moved to Lake Chad about 8,000 years ago. We also see that people from outside Africa have added to the African gene pool. For example, the Beja people in the Sahara have a lot of Middle Eastern DNA.

Europe

DNA analysis shows that modern humans moved into Europe and Asia in one big event between 60,000 and 70,000 years ago. Genetic evidence suggests people arrived in the Near East and Europe no earlier than 50,000 years ago.

Much of the work in archaeogenetics looks at the Neolithic transition in Europe. This was when people started farming. Early ideas suggested a huge number of farmers from the Near East moved into Europe. However, DNA studies in the 1990s showed that most European DNA came from groups already living there. Only a small part came from Near Eastern farmers. Most European DNA lines can be traced back to groups who moved back into northern Europe after the last Ice Age. Studies of ancient DNA also show that people started dairying (using milk) before many people could digest milk (lactose tolerance).

South Asia

South Asia was a major path for modern humans moving out of Africa. Some studies suggest the first people in India were Austro-Asiatic speakers. They arrived about 45,000 to 60,000 years ago. The Indian gene pool also has DNA from West and Central Asian groups who arrived later.

Interestingly, DNA studies show that mostly men took part in these later migrations. This is because there's less variety in female-inherited DNA compared to male-inherited DNA.

East Asia

DNA studies suggest that the first big move out of Africa went through Saudi Arabia and the Indian coast. This happened 50,000 to 100,000 years ago. A second big move happened 15,000 to 50,000 years ago, north of the Himalayas.

Scientists have also studied how people moved within East Asia. By comparing DNA from northeastern and southeastern groups, they found that many groups in northeast Asia came from the southeast. This supports the idea that East Asia was mostly settled from south to north. Archaeogenetics has also studied hunter-gatherer groups like the Ainu in Japan and Negrito groups in the Philippines. For example, Negrito groups in Malaysia and the Philippines are more closely related to local non-Negrito people than to each other. This suggests they might have mixed with local populations.

Americas

Archaeogenetics helps us understand how the Americas were populated from Asia. Native American DNA groups are thought to be between 15,000 and 20,000 years old.

Many ideas exist about how the Americas were settled. The most common idea is "three waves" of migration after the last Ice Age, crossing the Bering Strait. But genetic data has led to other ideas. For example, one idea suggests a migration from Siberia to South America 20,000 to 15,000 years ago. Another migration happened after the glaciers melted. DNA studies also show that the Americas were settled by small founding groups of people.

Australia and New Guinea

Archaeogenetics has also looked at how Australia and New Guinea were settled. The native people of Australia and New Guinea look very similar. But DNA shows this is because they adapted to similar living conditions. Their DNA shows "no similarities" between the two groups. This means they don't share a recent common ancestor.

DNA studies suggest that the two groups split over 50,000 years ago. This casts doubt on the idea that they shared a recent common history.

Plants and Animals

Archaeogenetics has been very useful in understanding how plants and animals became domesticated.

Plant Domestication

By combining genetics and archaeological finds, scientists can trace the earliest signs of plant domestication around the world. Different parts of a plant's DNA change at different rates. This can make it tricky to trace their family history. However, Nuclear DNA is often used because it changes faster and has more variations.

Scientists have found "domestication genes" in crops. These are traits that humans specifically chose for or against. Some examples include:

• tb1 (teosinte branched1): Affects how corn plants branch.
• tga1 (teosinte glume architecture1): Makes corn kernels easier for humans to use.
• te1 (Terminal ear1): Affects the weight of kernels.
• fw2.2: Affects the weight in tomatoes.
• BoCal: Affects the flowers of broccoli and cauliflower.

Studying plant domestication also helps us learn about the first global trade. When new crops that were grown in one area are found far away, it shows that people were trading resources.

Animal Domestication

Archaeogenetics helps us study how animals became domesticated. By looking at the genetic differences in domesticated animals, scientists can find clues in their DNA. These clues tell us about the traits of their wild ancestors. This helps archaeologists tell the difference between wild and domesticated animal remains. Genetic studies can also help find the ancestors of domesticated animals.

Archaeogenetics has been used to track the domestication of pigs around the world. These studies also give us clues about early farmers. Methods of archaeogenetics have also helped us understand how dogs became domesticated. Genetic studies show that all dogs came from the gray wolf. However, we still don't know exactly when, where, or how many times dogs were domesticated. Some studies suggest multiple times, while others don't. Archaeological finds, like buried dogs, help us understand this complex past. As early humans domesticated dogs, more and more dog remains were found. This gives archaeologists more to study and also provides clues about early human culture.

See Also

In Spanish: Arqueogenética para niños