Homo Sapiens: Research methods

How do we know that humans have evolved from other species? An excavator? Yes, sometimes we find traces of prehistoric humans by chance, when doing something else. Like here, building a road. At other times, something shows up on satellite images, traces of a grave mound are found, or the shape of the landscape shows that it could have been a perfect place for a prehistoric settlement.

Oh, they seem to have found something! Pot sherds. They need to call an expert on prehistory: an archaeologist. The archaeologists dig a pit: a trench. The trench is square-shaped, with perfectly straight, vertical walls.

The walls are kind of…striped! There are layers of soil, decomposed leaves, sand, and hard packed gravel that built up over a long time. Exactly like when you bake a cake, the lowest layer comes first and the uppermost last. So, the archaeologists know that the bone they found in layer seven must have ended up there earlier than the pot sherds in layer one. The bone is older.

But they don't know how old the pot sherds or the bone are. They send their findings to a laboratory for further investigation. All animals and plants that live on earth take in a certain kind of carbon, which is a bit radioactive - Carbon 14. When the plant or animal dies, part of the carbon 14 starts to decay. By measuring the ratio of radioactive carbon 14 in a material that once lived, we can count how long ago it died.

This is called the C-14-method, and works well on everything from old logs, to pieces of bone, and food residues. Now the archaeologists know that the food residues on the pot sherds are 1,000 years old and that the bone in layer seven is 19,000 years old. They dig deeper! Look a cranium in layer 22. The archaeologists suspect that the cranium doesn’t belong to the species Homo sapiens.

They call their colleagues, the paleo-anthropologists, who are experts on early pre-humans. The cranium is stuck, as if in concrete, the paleo-anthropologists have to chip it loose. This layer has been subject to severe pressure for several hundred thousands of years. Materials that earlier were soft have been petrified. The cranium has become a fossil.

The cranium is old. Probably older than 50,000 years, and therefore the C-14 method won't work any longer. It is difficult to date any of the material from layer 22. But, the layers above and under the cranium: layers 21 and 23 consist of hard packed volcanic ash which was formed by two different volcanic eruptions. And volcanic ash can be dated.

This too is done by measuring the radioactivity, and how it has changed since the ash was first formed. The samples show that layer 21 is 300,000 years old and layer 23 is 400,000 years old. Now the researchers know that the layer in between was formed between 300,000 and 400,000 years ago. The cranium was found in the upper part of layer 22, which makes them believe it is approximately 300,000 years old. Maybe this individual died in the volcanic eruption, and was buried by the ash?

Now, the cranium is carefully investigated by bone experts, osteologists. They weigh, measure, and compare. They can determine if the cranium belongs to the species Homo sapiens, or if it’s from an extinct species. They can determine the sex of the individual, if it was ill when it died, and how big a brain it had. This cranium is in good condition, and has distinctive traits showing it is a female from the species neanderthalensis.

The cranium is so well preserved that they could even read the individual’s DNA from a tooth. The analysis of the DNA confirms that it was a woman, and that she lived approximately 300,000 years ago, and that she probably had brown eyes and red hair. Knowledge of Human development - evolution - is getting better all the time. Researchers from different fields - disciplines - cooperate and use different methods and techniques to better understand us and where we come from.