The First Americans
Crossing the land bridge
Today, Asia and North America are separated at their closest point by 85 kilometers (58 miles) of chilly ocean waters. But ocean levels were much lower 15,000 to 20,000 years ago, and a large land mass connected the continents, allowing the first of many waves of immigrants to cross into North America. Climate researchers say that massive sheets of ice covered the inland areas of present-day Canada, so the migrants must have stuck close to the Pacific coast in order to reach the ice-free regions of North and South America.
How Do We Know?
How can we retrace the footsteps of people who died 35,000 years ago? The smattering of artifacts and fossil remains from early groups of modern humans tells us much about their migrations. But experts also use DNA evidence to round out the story. What do these two kinds of evidence reveal about the first modern humans to arrive in Europe?
Fossils Tell Us:
Modern humans were living in Europe by 35,000 years ago.
Homo sapiens fossils provide tangible evidence of the arrival of modern humans in Europe. The oldest of these European fossils, found in southwestern Romania, is 35,000 years old, so experts know that modern humans had reached Europe by that time.
DNA Tells us:
The first modern humans in Europe came from the Middle East and from central Asia.
Over time, DNA changes, or mutates, through mistakes in DNA copying. These mutations are passed from parents to children to grandchildren and so on. So human DNA today carries a record of our ancestors' mutations, which allow scientists to tell people of different ancestry apart. We all have patterns of ancient mutations in our DNA that reveal where our ancestors came from.
A woman who migrated from the Middle East to Europe thousands of years ago passed a mitochondrial DNA mutation to her female descendants.
Millions of European women today carry the ancient mutation, and other mutations that arose later on.
DNA Tells Us:
Modern humans lived in Europe by around 40,000 to 30,000 years ago.
DNA mutations happen at a somewhat predictable rate, so patterns of mutations from several populations can help scientists estimate the date of an ancient migration. However, these dates are only estimates--fossil dates are much more reliable.