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Homo sapiens: Why are we the only human species left on the planet? | United States

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Three discoveries changed what we know about the origin of the human race and our own species, Homo sapiens. It is possible, some experts say, that we need to rethink this concept when it comes to referring to ourselves, as these new findings suggest that we may be a type of Frankenstein hybrid made up of pieces of other human species, with whom until relatively recently we shared our planet and produced offspring.

Discoveries made last week indicate that there were as many as eight different species or groups of humans 200,000 years ago. All of these are part of the Homo assignment, in which modern humans are included. Recent additions to human evolution feature an interesting mix of primitive features – huge arches above the eyebrows and flat heads – as well as modern features. The so-called “Dragon Man” or Homo longi discovered in China ”had a cranial capacity similar or superior to that of modern humans. The Nesher Ramla Homo, discovered in Israel, could have come from a species that predated and contributed to European Neanderthals and East Asian Denisovans, with whom our own species had repeated sexual relations producing mixed-race children who were accepted by their tribes as another member of the family.

Today we know that because of this mixing, every modern human beyond the African continent carries 3% Neanderthal DNA and that the people of Tibet carry genes that allow them to live at high altitudes that have been transmitted by the Denisovans. Genetic analysis of the current population of New Guinea suggests that the Denisovans – a branch of the Neanderthal family tree – existed as little as 15,000 years ago, a blink of an eye in terms of evolution.

An x-ray image of the jawbone of Nesher Ramla ‘Homo.’Ariel Pokhojaev

The third great discovery made in recent days could have concerned an episode of a police show. Researchers analyzed DNA preserved in the soil of Denisova Cave in Siberia and found genetic material from native humans, Denisovans, Neanderthals and Homo sapiens dating from periods so close that they could all have overlapped. Three years ago, the remains of the first known hybrid of two human species were discovered in one place: the daughter of a Neanderthal and a Denisovan.

Paleoanthropologist Florent Detroit gave science one of these new human species when he identified Homo luzonensis, who lived on an island in the Philippines 67,000 years ago and exhibited a curious mix of characteristics that could be the result of a long evolution of more than a million years, passed without contact with other early humans. It’s a story similar to that of his contemporary, Homo floresiensis, or Flores Man, a human species barely one and a half meters tall who lived on the Indonesian island. Flores’ man had a brain the same size as a chimpanzee, but if we apply the intelligence test most commonly used by paleoanthropologists, we can say that he was as advanced as sapiens and used stone tools of equal evolutionary craftsmanship.

To these two islanders are added homo erectus, the first human traveler who left Africa two million years ago, spread throughout Asia and existed there less than 100,000 years ago. The eighth player in this story is Homo daliensis, whose fossilized remains were found in China and which was a mixture of erection and sapiens, even if daliensis can still be attributed to the recently named line of Homo longi.

“It doesn’t surprise me that there have been multiple species of humans alive at the same time,” says Detroit. “If we take into account the last geological age, which began 2.5 million years ago, there have always been different races and species of hominoids sharing the planet. The big exception is today: never before has a single human species existed alone on earth. “

Why is sapiens the last human standing? For Juan Luis Arsuaga, a paleoanthropologist working at the Atapuerca archaeological site in northern Spain, the answer is community. “We are a hyper-social species, the only one capable of building bonds beyond kinship, unlike the rest of mammals. We share consensual stories like country, religion, language, football teams; and we are willing to sacrifice a lot for them. Even the Neanderthals, our closest relatives, who fashioned ornaments, symbols and art, did not share this behavior. “Neanderthals did not have a flag,” Arsuaga notes. For reasons still unknown, the Neanderthals became extinct about 40,000 years ago.

The Sapiens were not “superior in the strict sense” to their contemporaries, explains Antonio Rosas of the Spanish National Research Council (CSIC). “Today we know that we are the result of hybridizations with other species and the combination of characteristics that we have has proven to be perfect for that time.” Another possible additional benefit is that Homo sapiens lived in larger groups than Neanderthals, which would lead to less inbreeding and better general health of populations.

Detroit believes part of the explanation lies in the very essence of sapiens, which means wise in Latin. “We have a huge brain that we have to feed, as such we need a lot of resources and therefore a lot of territory. Homo sapiens experienced a vast population expansion and it is very likely that the competition for territory was too tough for the rest of the species, ”says Detroit.

María Martinón-Torres, director of the Spanish National Center for Research on Human Evolution, believes that the secret to Homo sapiens’ success is “hyper adaptability”. “Ours is an invasive species and although not necessarily ill-intentioned, we have been an evolutionary Attila the Hun,” said Martinón-Torres. “At our pace and because of our way of life, biodiversity has declined, including that of humans. We are one of the most influential ecological forces on the planet and this story, our story, began to take shape in the Pleistocene. [the geological period from 2.5 million years ago to 10,000 years ago, when Homo sapiens were the only remaining human species in existence].

Excavations at the Nesher Ramla site in Israel.
Excavations at the Nesher Ramla site in Israel.Zaidner

Recent discoveries have served to fuel a growing problem: Scientists are naming more and more human species, but does it make sense to do so? From the perspective of Israel Hershkovitz, an Israeli paleoanthropologist who made the discovery at the Nesher Ramla archaeological site, the answer is no. “There are too many species,” he said. “The classic definition is that two different species cannot have fertile children. DNA tells us that Homo sapiens, Neanderthals and Denisovans had such children, in which case they should be considered the same species.

“If we are sapiens, then these species which are our ancestors by mixture are also sapiens», Notes João Zilhão, professor at the University of Barcelona at the Catalan Institution for Research and Advanced Studies.

This question has become a source of confrontation between experts. José María Bermúdez de Castro, co-director of the Atapuerca site, underlines that “hybridization is very common among existing species, especially in the plant world. The concept of species can be nuanced, but I don’t think we should abandon it because it is very useful in helping us to understand.

Many factors come into play in this debate. The obvious differences between Homo sapiens and Neanderthals are not the same as the identity of a species such as Homo luzonensis, of which only a few teeth and bones have been discovered, or the Denisovans, most of the information available from which comes from DNA extracted from tiny fossils.

“Strangely enough, despite the frequent contact between them, Homo sapiens and Neanderthals were perfectly recognizable and distinguishable species until the end, ”explains Martinón-Torres. “The features of the late Neanderthals are more marked than their predecessors, rather than having become less distinct as a result of mixing. There have been biological exchanges, and perhaps cultural ones, but none of these species have ceased to be themselves: distinct, biologically and visually identifiable, with their specific adaptations and ecological niche in the history of evolution. I believe this is the best example that hybridization does not necessarily conflict with the concept of species.

Martinón-Torres’ colleague Hershkovitz believes the debate will continue, however: “We are digging in three other caves in Israel where we have found human fossils which will give a new perspective to human evolution,” he says.

English version by Rob Train.


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