Frog evolution linked to dinosaur asteroid strike

Frog evolution linked to dinosaur asteroid strike

With fossils and DNA, scientists collect an image of the beginnings of humanity, a story of origin with more laps than anything you find in the movies.

The current consensus is that the experts Homo sapiens evolved there are at least 300,000 years in Africa. Only later, there are about 70 000 years, a small group of Africans settled in other continents, which led to other populations today.

Johannes Krause, director of the Max Planck Institute for the History of Humanity in Germany, this divergence tends mainly. “Why have not people left Africa before?” He asked in an interview. After all, he noted, the continent is physically linked to the Middle East. You could go.

In a study published Tuesday in the journal Nature Communications, Dr. Krause and his colleagues report that Africans have abandoned – there are more than 270,000 years.

Based on newly discovered DNA in fossils, the researchers conclude that a wave of early Homo sapiens or relatives of our species makes its way from Africa to Europe. There they crossed paths with the Neanderthals.

Then the old African immigrants have disappeared. But part of their DNA has been subjected to the next generations of Neanderthals.

“This is now a complete picture,” said Dr. Krause. “Gather all the elements.”

Since the 19th century, paleontologists have had difficulty understanding how Neanderthals relate to us. The fossils show that they were anatomically distinct, with a heavy forehead, a strong body and a number of subtler features missing.

The oldest Neanderthal bones of individuals found in a Spanish cave called Sima de los Huesos, date back 430,000 years. More recently, Neandertal dates back to about 100,000 years, it is found in Europe and southern Siberia.

After 40,000 years, Neanderthals disappear from fossil records.

As a graduate student in the mid-2000s, Dr. Krause visited museums to drill fragments of fossil Neanderthal bones. In some of them, he and his colleagues were able to find fragments of DNA that they could study.

The excavations at the entrance of the Hohlenstein-Stadel cave in 1937, found the year of the Neanderthal femur. Ulm Credit Museum
Scientists studying ancient genes are looking for two types of genetic material.

The vast majority of our genes are in a pocket in every so-called cell nucleus. We inherited so-called nuclear DNA from both parents.

But we also carry a small amount of DNA in the fuel generation plants of our cells called mitochondria. We inherited mitochondrial DNA only from our mothers, because a father’s sperm destroyed his own mitochondrial DNA during fertilization.

A few years ago, Dr. Krause and his colleagues began looking for old Neanderthal genes in a fossil in search of mitochondrial DNA. After discovering the mitochondrial DNA in some fossils, later they were able to find nuclear DNA.

Genes have been surprises. For example, DNA fragments in people living with non-African origin come from Neanderthals. When modern humans have evolved in Africa, it seems they have crossed several times Neanderthal.

These children have become a part of human society, the transmission of their genes.

But a finger and a tooth from a Siberia cave called Denisova left Dr. Krause and his colleagues with a baffling enigma.

Within these fossils, scientists have found mitochondrial DNA sequences that were not human or Neanderthal, but something else – a distant branch of the family tree. Neanderthal mitochondrial DNA was much closer to ours.

Later, researchers were able to recover the finger bone Denisovan nuclear DNA, which showed that Denisovans and Neanderthals were more closely related to each other.

As scientists have found more ancient fossil DNA, our history has grown. Scientists now believe that the common ancestor of modern humans, Neanderthals and Denisovans, lived between 765,000 and 550,000 years.

There are about 445 000 to 473 000 years, the descendants of the common ancestor divided into two lineages. It eventually led to modern humans, while the other led Neandertal and Denisovans.

However, after years of research, Dr. Krause still did not understand why nuclear DNA and mitochondrial DNA from Neandertals appeared to have a different background. The first shows a link with De

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