Homo Sapiens: Anatomically Modern Humans (AMH)

IN 1996 ARCHAEOLOGISTS ventured into a cave in Gibraltar, where they found a burial containing human bones. Among them was a skull.



The archaeologists knew that the burial was very old. It was discovered under layers of sediment containing fish, bird, and mammal bones and carved flint objects. The skull had been damaged after the burial, but it still joined the collection of the Gibraltar National Museum.

The skull’s age remained a mystery for many years. In 2019 the results of a landmark study proved through DNA analysis that it belonged to a woman who lived 7,500 years ago, making it the oldest remnant of a modern female woman found in Gibraltar to date.

Analysis also revealed that the skull’s genetic ancestry lay far east of the Iberian Peninsula. The presence of genes from across the Mediterranean gave archaeologists new clues about how ancient humans traveled when agriculture was spreading through Europe.





Story of the skull
When Calpeia’s skull was found in 1996, it was impossible to glean much information from it. Gibratar’s humid climate leads to a rapid deterioration of DNA, and the possibilities of extracting useful genetic material seemed unlikely at the time. DNA analysis was in its infancy, and the damage to the skull made it difficult to study.

By 2019 the study of ancient DNA had made great strides. The journal Science published the genome analysis of 271 inhabitants of Spain, Gibraltar, and Portugal, including the 1996 skull. Under the coordination of Harvard Medical School, researchers were successfully able to extract viable samples of ancient DNA.



The results told the researchers a great deal: The skull belonged to a woman who lived around 5400 B.C.—many millennia after the Neanderthals of Gibraltar had become extinct. She was slightly built, light-skinned, with dark hair and eyes. She was also lactose intolerant (a common trait for that period).

Dated to 7,500 years ago, Calpeia’s life corresponds to the later Neolithic period. She lived at a time when agriculture and raising livestock were spreading across the Iberian Peninsula, displacing the old hunter-gatherer model. Her lactose intolerance indicates that dairy farming was most likely not part of her culture.

Calpeia’s age when she died cannot be determined precisely from the skull. Her cranial sutures—the fibrous joints connecting the bones of the skull—suggest that she was an adult, somewhere between 25 and 40 years of age. (Watch how researchers reconstructed the face of Avgi, a 9,000-year-old teenager.)



Head West
Researchers were most excited about what DNA revealed about Calpeia’s ancestry. Only 10 percent of Calpeia’s genome comes from the population found in the Iberian Peninsula, while the remaining 90 percent has its origin in Anatolia, modern-day Turkey. Farmers from Anatolia during the Neolithic period had a high percentage of alleles for dark eyes and light skin. By contrast, hunter-gatherers from central and western Europe show genetic markers for dark skin and light eyes.
time.

Archaeologists believe that agriculture developed in several areas of the world at roughly the same time. Anatolia was one of the global centers of the Neolithic revolution. From there, techniques for crop farming and animal husbandry slowly spread westward across the Mediterranean world and into Europe.

The high proportion of Anatolian components in Calpeia’s DNA suggests that her Anatolian origins were recent. It is likely that Calpeia—or her parents or very recent ancestors—journeyed from Anatolia to Gibraltar by sea.

If Calpeia’s people had traveled by land, their progress westward would have taken years or generations. Their DNA would have mixed with local populations along the way, making Calpeia’s resulting genome more diverse.

To understand how Homo sapiens eventually evolved from these older lineages of hominins, the group including modern humans and our closest extinct relatives and ancestors, scientists are unearthing ancient bones and stone tools, digging into our genes and recreating the changing environments that helped shape our ancestors’ world and guide their evolution.

These lines of evidence increasingly indicate that H. sapiens originated in Africa, although not necessarily in a single time and place. Instead it seems diverse groups of human ancestors lived in habitable regions around Africa, evolving physically and culturally in relative isolation, until climate driven changes to African landscapes spurred them to intermittently mix and swap everything from genes to tool techniques. Eventually, this process gave rise to the unique genetic makeup of modern humans.

“East Africa was a setting in foment—one conducive to migrations across Africa during the period when Homo sapiens arose,” says Rick Potts, director of the Smithsonian’s Human Origins Program. “It seems to have been an ideal setting for the mixing of genes from migrating populations widely spread across the continent. The implication is that the human genome arose in Africa. Everyone is African, and yet not from any one part of Africa.”

New discoveries are always adding key waypoints to the chart of our human journey. This timeline of Homo sapiens features some of the best evidence documenting how we evolved.

550,000 to 750,000 Years Ago: The Beginning of the Homo sapiens Lineage



Genes, rather than fossils, can help us chart the migrations, movements and evolution of our own species—and those we descended from or interbred with over the ages.

The oldest-recovered DNA of an early human relative comes from Sima de los Huesos, the “Pit of Bones.” At the bottom of a cave in Spain’s Atapuerca Mountains scientists found thousands of teeth and bones from 28 different individuals who somehow ended up collected en masse. In 2016, scientists painstakingly teased out the partial genome from these 430,000-year-old remains to reveal that the humans in the pit are the oldest known Neanderthals, our very successful and most familiar close relatives. Scientists used the molecular clock to estimate how long it took to accumulate the differences between this oldest Neanderthal genome and that of modern humans, and the researchers suggest that a common ancestor lived sometime between 550,000 and 750,000 years ago.

Pinpoint dating isn't the strength of genetic analyses, as the 200,000-year margin of error shows. “In general, estimating ages with genetics is imprecise,” says Joshua Akey, who studies evolution of the human genome at Princeton University. “Genetics is really good at telling us qualitative things about the order of events, and relative time frames.” Before genetics, these divergence dates were estimated by the oldest fossils of various lineages scientists found. In the case of H. sapiens, known remains only date back some 300,000 years, so gene studies have located the divergence far more accurately on our evolutionary timeline than bones alone ever could.

Though our genes clearly show that modern humans, Neanderthals and Denisovans—a mysterious hominin species that left behind substantial traces in our DNA but, so far, only a handful of tooth and bone remains—do share a common ancestor, it’s not apparent who it was. Homo heidelbergensis, a species that existed from 200,000 to 700,000 years ago, is a popular candidate. It appears that the African family tree of this species leads to Homo sapiens while a European branch leads to Homo neanderthalensis and the Denisovans.

More ancient DNA could help provide a clearer picture, but finding it is no sure bet. Unfortunately, the cold, dry and stable conditions best for long-term preservation aren’t common in Africa, and few ancient African human genomes have been sequenced that are older than 10,000 years.

“We currently have no ancient DNA from Africa that even comes near the timeframes of our evolution—a process that is likely to have largely taken place between 800,000 and 300,000 years ago,” says Eleanor Scerri, an archaeological scientist at the Max Planck Institute for the Science of Human History in Germany.

300,000 Years Ago: Fossils Found of Oldest Homo sapiens



As the physical remains of actual ancient people, fossils tell us most about what they were like in life. But bones or teeth are still subject to a significant amount of interpretation. While human remains can survive after hundreds of thousands of years, scientists can’t always make sense of the wide range of morphological features they see to definitively classify the remains as Homo sapiens, or as different species of human relatives.

Fossils often boast a mixture of modern and primitive features, and those don’t evolve uniformly toward our modern anatomy. Instead, certain features seem to change in different places and times, suggesting separate clusters of anatomical evolution would have produced quite different looking people.

No scientists suggest that Homo sapiens first lived in what’s now Morocco, because so much early evidence for our species has been found in both South Africa and East Africa. But fragments of 300,000-year-old skulls, jaws, teeth and other fossils found at Jebel Irhoud, a rich site also home to advanced stone tools, are the oldest Homo sapiens remains yet found.

The remains of five individuals at Jebel Irhoud exhibit traits of a face that looks compellingly modern, mixed with other traits like an elongated brain case reminiscent of more archaic humans. The remains’ presence in the northwestern corner of Africa isn’t evidence of our origin point, but rather of how widely spread humans were across Africa even at this early date.

Other very old fossils often classified as early Homo sapiens come from Florisbad, South Africa (around 260,000 years old), and the Kibish Formation along Ethiopia’s Omo River (around 195,000 years old).

The 160,000-year-old skulls of two adults and a child at Herto, Ethiopia, were classified as the subspecies Homo sapiens idaltu because of slight morphological differences including larger size. But they are otherwise so similar to modern humans that some argue they aren’t a subspecies at all. A skull discovered at Ngaloba, Tanzania, also considered Homo sapiens, represents a 120,000-year-old individual with a mix of archaic traits and more modern aspects like smaller facial features and a further reduced brow.

Debate over the definition of which fossil remains represent modern humans, given these disparities, is common among experts. So much so that some seek to simplify the characterization by considering them part of a single, diverse group.

“The fact of the matter is that all fossils before about 40,000 to 100,000 years ago contain different combinations of so called archaic and modern features. It’s therefore impossible to pick and choose which of the older fossils are members of our lineage or evolutionary dead ends,” Scerri suggests. “The best model is currently one in which they are all early Homo sapiens, as their material culture also indicates.”

As Scerri references, African material culture shows a widespread shift some 300,000 years ago from clunky, handheld stone tools to the more refined blades and projectile points known as Middle Stone Age toolkits.

So when did fossils finally first show fully modern humans with all representative features? It’s not an easy answer. One skull (but only one of several) from Omo Kibish looks much like a modern human at 195,000 years old, while another found in Nigeria’s Iwo Eleru cave*, appears very archaic, but is only 13,000 years old. These discrepancies illustrate that the process wasn’t linear, reaching some single point after which all people were modern humans.

*https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0024024