The scientists in Sima de los Huesos, Spain have unearthed a fossil that contains the oldest living DNA evidence of humans dating back 400,000 years. The surprise is that the DNA matches that of a species of humans known as Denisovans located in Siberia, about 4,000 miles east of the site in Spain.
ESL Voices Lesson Plan for this post with Answer Key
Excerpt: Baffling 400,000-Year-Old Clue to Human Origins By Carl Zimmer New York Times Science
“Scientists have found the oldest DNA evidence yet of humans’ biological history. But instead of neatly clarifying human evolution, the finding is adding new mysteries.
In a paper in the journal Nature, scientists reported Wednesday that they had retrieved ancient human DNA from a fossil dating back about 400,000 years, shattering the previous record of 100,000 years.
The mismatch between the anatomical and genetic evidence surprised the scientists, who are now rethinking human evolution over the past few hundred thousand years. It is possible, for example, that there are many extinct human populations that scientists have yet to discover… Right now, we’ve basically generated a big question mark,” said Matthias Meyer, a geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and a co-author of the new study.
Hints at new hidden complexities in the human story came from a 400,000-year-old femur found in a cave in Spain called Sima de los Huesos (“the pit of bones” in Spanish). The scientific team used new methods to extract the ancient DNA from the fossil.
Finding such ancient human DNA was a major advance, said David Reich, a geneticist at Harvard Medical School who was not involved in the research. “That’s an amazing, game-changing thing,” he said.
When Dr. Meyer and his colleagues drilled into the femur, they found ancient human DNA inside, just as they had hoped. Our expectation was that it would be a very early Neanderthal,” Dr. Meyer said.
But the DNA did not match that of Neanderthals. Dr. Meyer then compared it to the DNA of the Denisovans, the ancient human lineage that he and his colleagues had discovered in Siberia in 2010. He was shocked to find that it was similar. Everybody had a hard time believing it at first, Dr. Meyer said. So we generated more and more data to nail it down.
The extra research confirmed that the DNA belonged on the Denisovan branch of the human family tree. The new finding is hard to reconcile with the picture of human evolution that has been emerging based on fossils and ancient DNA…
Based on previously discovered ancient DNA and fossil evidence, scientists generally agreed that humans’ direct ancestors shared a common ancestor with Neanderthals and Denisovans that lived about half a million years ago in Africa.
Their shared ancestors split off from humans’ lineage and left Africa, then split further into the Denisovans and Neanderthals about 300,000 years ago. The evidence suggested that Neanderthals headed west, toward Europe, and that the Denisovans moved east.
Humans’ ancestors, meanwhile, stayed in Africa, giving rise to Homo sapiens about 200,000 years ago. Humans then expanded from Africa into Asia and Europe about 60,000 years ago. They then interbred not only with Neanderthals, but with Denisovans, too. Later, both the Denisovans and Neanderthals became extinct. Dr. Arsuaga doubts that Denisovans were spread out across so much of the Old World, from Spain to Siberia, masquerading as Neanderthals.
One alternative explanation is that the humans of Sima de los Huesos were not true Neanderthals, but belonged to the ancestors of both Denisovans and Neanderthals. It is also possible that the newly discovered DNA was passed to both Neanderthals and Denisovans, but eventually disappeared from Neanderthals, replaced by other variants…
This complicated story has come to light only because of advances over the past 20 years in retrieving ancient DNA. When an organism dies, its DNA breaks down into smaller and smaller fragments, while also becoming contaminated with the DNA of other species like soil bacteria. So piecing the fossil DNA together is a bit like putting together a jigsaw puzzle created by a sadist.
Meanwhile, using improved methods, Dr. Paabo, Dr. Meyer and their colleagues assembled a rough draft of the entire Neanderthal genome in 2010.” Read more…
Level: Intermediate -Advanced
Language Skills: Reading, writing, and speaking. Vocabulary and grammar activities are included.
Time: Approximately 2 hours.
Materials: Student handouts (from this lesson) access to news article, and video.
Objective: Students will read the article with a focus on improving reading comprehension and learning new vocabulary. At the end of the lesson students will express their personal views on the topic through discussions, and writing.
I. Pre-Reading Activities
Analyzing headings and photos
Directions: Ask students to read the title of the post and of the actual article they are about to read. Then, have them examine the photos. Based on these sources, ask students to create a list of words and ideas that they think might be related to this article.
II. While Reading Activities
Directions: Students are to infer the meanings of the words in bold taken from the article. They may use a dictionary, thesaurus, and Word Chart by Freeology for assistance.
- Instead of neatly clarifying human evolution, the finding is adding new mysteries.
- Scientists retrieved ancient human DNA from a fossil dating back about 400,000 years.
- The fossil, a thigh bone had seemed to belong to a forerunner of Neanderthals.
- It most closely resembles DNA from an enigmatic lineage of humans known as Denisovans.
- The mismatch between the anatomical and genetic evidence surprised the scientists.
- The scientific team used new methods to extract the ancient DNA from the fossil.
- Based on the anatomy of the fossils, Dr. Arsuaga has argued that they belonged to ancestors of Neanderthals.
- Everybody did not believe it so we generated more and more data to nail it down.
- The new finding is hard to reconcile with the picture of human evolution.
- Their shared ancestors split off from humans’ lineage.
Directions: Review the following statements from the reading. If a statement is true they mark it T. If the statement is not applicable, they mark it NA. If the statement is false they mark it F and provide the correct answer.
- Scientists have found the oldest DNA evidence in the Netherlands.
- The human DNA is from a fossil dating back about 400,000 years.
- Instead of clarifying human evolution, the finding is adding new mysteries.
- The DNA closely resembles DNA from a lineage of humans known as Denisovans located in Spain.
- Now, scientists think that there are fewer extinct human populations yet to discover.
- Matthias Meyer is a geneticist at the Max Planck Institute for Evolutionary Anthropology at Harvard University.
- Since the 1970s, Spanish scientists have brought out a wealth of fossils from the cave dating back hundreds of thousands of years.
- There have been many fossils of children.
- Scientists generally agreed that humans’ direct ancestors shared a common ancestor that lived about half a million years ago in Europe.
- This complicated story has come to light only because of advances over the past 20 years in retrieving ancient DNA.
Structure and Usage
Directions: The following groups of sentences are from the article. One of the sentences in each group contains a grammatical error. Students are to identify the sentence (1, 2, or 3 ) from each group that contains the grammatical error.
- Scientists has found the oldest DNA evidence.
- The finding is adding new mysteries.
- The fossil, a thigh bone was found in Spain.
- It most closely resembles DNA from an lineage of humans.
- The mismatch between the evidence surprised the scientists.
- They might have interbred, swapping DNA.
- Finding such ancient human DNA was a major advance.
- This would not have be possible even a year ago.
- Since the 1970s, Spanish scientists have brought out fossils from the cave.
III. Post Reading Tasks
Reading Comprehension Check
Directions: Have students use the WH-question format to discuss or to write the main points from the article.
Who or What is the article about?
Where does the action/event take place?
When does the action/event take place?
Why did the action/event occur?
How did the action/event occur?
Directions: Place students in groups and have them answer the following questions. Afterwards, have the groups share their thoughts as a class. As an assignment for homework have the groups choose 1 or 2 topics and prepare a short paper to present in class.
- How would you put the following statement into your own words? “Based on previously discovered ancient DNA and fossil evidence, scientists generally agreed that humans’ direct ancestors shared a common ancestor with Neanderthals and Denisovans that lived about half a million years ago in Africa.”
- The article states, “The scientific team used new methods to extract the ancient DNA from the fossil” Do you think it would be possible for scientists to reconstruct the humans from this ancient DNA? Provide reasons for your answer.
- How does this new information relate to humans today? What is the importance?
- What is a fossil?
- What exactly is DNA?
- Research the new methods that scientist used to extract this DNA and share your findings with the class.