To unthaw or to unthaw? That is the question. Introducing my favorite word in the English language, “unthaw” has two meanings; 1)…
This year—2022—has been another exciting year for research in human evolution. With many projects around the world proceeding despite the COVID pandemic, there were multiple exciting discoveries and breakthroughs in a variety of fields. From telling us more about our food, our health, our close relatives and ancestors, and even our animal friends, these new discoveries shed more light on what it means to be human.
Meat, fire, and beer: the origins of our modern food staples and how they shaped our species
For decades one of the hallmarks of human evolution has been the presumed shift from a predominantly plant-based diet, as in chimpanzees and gorillas, to one that included significant amounts of meat and animal tissue. This led to the idea that since meat is generally more nutrient dense, more meat-eating could have allowed our ancestors to evolve the large and energetically demanding brains that we associate with our own species, beginning with the emergence of Homo erectus around 2 million years ago. But is there actually an increase in meat consumption after this time, inferred by stone tool butchery marks on fossilized bones, or is there just more fossil material overall – making it more likely to find these butchery marks? In January, Andrew Barr from The George Washington University and colleagues explored this question by examining all the fossil evidence for butchery in eastern Africa from 1.2 million years ago and older. They concluded that the evidence for increased carnivory in our ancestors is merely an effect of increased sampling of the archaeological record at certain time intervals starting around 2 million years ago, meaning that there is no strong relationship between eating more meat and the evolution of larger brains in our ancestors.
Well, if it wasn’t meat eating that enabled big brains to evolve… maybe it was cooking? Cooking makes food easier to digest and allows us to extract more nutrients from our food while expending less energy. While the earliest evidence for human control of fire dates back to at least 1 million years ago, the earliest evidence for cooking food was much more recent. In November, a team led by Irit Zohar from Tel Aviv University made new discoveries from the site of Gesher Benot Ya’aqov in Israel which push this date back to around 600,000 years ago with evidence for hominins cooking fish! Teeth of a species of carp were subjected to temperatures required to cook fish, but not as hot as temperatures directly inside a fire would be. This indicates the fish were placed above or next to the fire for cooking rather than being discarded in the fire or burned accidentally.
Of course, what good is BBQ without a tasty beverage to wash it down? Published in December 2021 (after last year’s post was written), a team led by Jiajing Wang from Dartmouth University uncovered the oldest known beer production in the world in Egypt. Made of fermented grains, the production of beer is closely linked to the emergence and spread of agricultural societies. Dating to 5,800 years ago, hundreds of years before Egypt’s first pharaoh, this beer was thick like a porridge rather than watery and probably used for both daily consumption and ritual purposes. Yum?
Animal friends…and animal food: origins of domestication and cooperation
Whether for work, companionship, or food, modern human existence would not be possible without domesticated animals. But do human impacts on animal communities in a broader sense date back far earlier than evidence for domestication? In July, a team led by Danielle Frasier from the Canadian Museum of Nature quantified species evenness in North America over the past 20,000 years, and found that there were two pulses of diversity decrease among animal communities: the first around 10,000 years ago associated with the North American megafauna extinction, and another around 2,000 years ago during a period in which agriculture spread rapidly and population sizes boomed. This study demonstrates that humans can affect, and have affected, animal communities in indirect ways in addition to hunting and domestication.
When it comes to domesticated animals, perhaps none captures the imagination and our emotions like “humankind’s best friend:” the dog. Dogs are also currently the earliest known domesticated animal on Earth. A June study led by Anders Bergström and Pontus Skoglund of The Francis Crick Institute looked at genomes of ancient wolves, from whom our species domesticated the modern dog, to try and determine where and when the connection between humans and dogs began. They found that ancient wolf populations in North America, Europe, and Siberia were interconnected with each other in the past rather than being separate populations like today, and that all dogs included in the study are most closely related to wolves from eastern Eurasia than western Eurasia. However, dogs originating from the Near East and Africa have significant contributions to their genomes from ancient wolves in Southwest Eurasia – either indicating a separate domestication process or, more likely, interbreeding with that additional wolf population early in the domestication process (just how early members of our own species interbred with Neanderthals when we first left Africa). While this study points strongly to eastern Eurasia as the geographic source of modern dogs, none of the ancient wolf populations studied were the direct ancestor of modern dogs, meaning that the true dog ancestor (or ancestors) remains to be found.
In addition to companionship, humans also domesticated animals for food and to assist with work. Another study in June led by Joris Peters from Ludwig Maximilian University Munich and Greger Larson from University of Oxford traced the origin of chicken domestication to around 1650 BCE in Thailand, corresponding to the spread of grains (specifically rice and millet). Chickens then appear to follow the grains as they spread around the world as a food source. Clearly, modern humans owe a lot to our animal friends and new finds continue to shed light on where, when, and how these interspecies interactions first emerged.
New fossils shed light on old ancestors: discoveries from our earliest and most recent evolutionary history
As in previous years, 2022 gave us more new fossil finds to tell us about our human lineage’s earliest history. One of the first possible hominins, Sahelanthropus tchadensis, dates to around 6-7 million years ago and was found in Chad in central Africa. Previously known only by cranial remains and a partial femur, in August a team led by Guillaume Daver and Franck Guy from Université de Poitiers reinterpreted the femur (upper leg bone) and described two ulnae (forearm bones) of this species. These ulnae share many affinities with our ape relatives and suggest that while Sahelanthropus may have been bipedal on the ground, its arms were still well adapted to climbing and clambering in trees.
On the more recent side of prehistory: new fossils of the enigmatic Denisovans, known mostly from their DNA, are starting to tell us more about where they lived and what they looked like. Following up on a Denisovan mandible found in Tibet in 2019, a Denisovan molar was recently discovered in Laos, southeast Asia. Dating to between 130,000 to 160,000 years old, this is the first Denisovan fossil found in a geographic area that scientists now know their DNA wound up. Many populations of modern southeast Asian, Papuan, and Filipino people have some Denisovan DNA in them – up to 5% in one indigenous Filipino group. We’re looking forward to more new finds of Denisovan fossils to tell us more about who they were, what they looked like, as well as when and how they interacted with our own species.
Speaking of species interactions, new finds in February from a cave in southeast France are complicating the story of human-Neanderthal co-occupation of Europe. A team led by Ludovic Slimak from Université de Toulouse unearthed evidence of hominin occupation at a site called Grotte Mandrin in France: first Neanderthals were there, then modern humans, then Neanderthals again before modern humans became the only hominin in Europe. From both lithic and fossil evidence, this modern human occupation dates to older than 50,000 years ago, almost 10,000 years older than the previous record for modern humans in this region. This evidence tells us that not only did Neanderthals and modern humans live in the same area for a long span of time (potentially implying that our presence in Europe did not drive Neanderthals to extinction), but also that these two species occupied the same site alternately. This extended time span of interaction could have implications for genetics as well, potentially adding another data point to the where and when of modern human-Neanderthal interbreeding.
Friends and family ties in modern apes and Neanderthals
While most studies of apes focus on groups of only one species at a time, some apes, like chimpanzees and gorillas, actually overlap in multiple locations – providing an opportunity to observe the interactions between them. Often when two closely related species overlap in range, their actions are predominantly antagonistic, or aggressive, to the other group. But in the Nouabalé-Ndoki National Park in the Republic of Congo, chimpanzees and gorillas have been observed being downright friendly with each other! From the two species foraging in the same tree, to their young playing with each other, to individuals forming lasting friendships, chimps and gorillas have generally gotten along over the 20-year period of study led by Crickette Sanz of Washington University and announced in October. This between-species cooperation may have a large advantage in deterring predators like leopards and in helping each other find valuable food sources.
While it is relatively straightforward to observe group dynamics in living apes, figuring out how now-extinct early human groups lived and interacted is much trickier, as population-level studies require multiple fossils from the same site at the same time period. Between two cave sites in southern Siberia (Chagyrskaya and Okladnikov Caves), in October a team led by Laurits Skov and Benjamin Peter from the Max Planck Institute for Evolutionary Anthropology sequenced nuclear, mitochondrial, and Y-chromosome DNA of 13 Neanderthal individuals. From these sequences, they determined that two of the Neanderthals represent a father-daughter pair and that another two are cousins. Additionally, evidence points to one third of the Neanderthals being part of the same tightly knit community living around 54,000 years ago. Such small-scale resolution is almost unheard of in paleoanthropology! Analysis of the Y-chromosome (passed on through males) and mitochondrial (passed on through females) DNA reveals that the individuals had significantly less diverse Y-chromosome DNA, indicating that Neanderthal females were the ones to relocate to different groups, diversifying the mitochondrial DNA gene pool – in much the same pattern as has been observed in living chimpanzees. These finds give us new insights into Neanderthal social structure, and potentially even to how interbreeding with our own species may have occurred.
How disease shapes us, and how we have evolved to treat it
“Modern medicine” is thought to have arisen at least by the time (and possibly as a result of) agriculture and large-scale population centers. More people means more disease, and humans would have looked for new ways to treat diseases. But something as medically complex as limb amputations were only known to occur as far back as 7,000 years ago and were not commonly known until a few hundred years ago, long after the rise of agricultural societies. However, a new find out of Borneo in Indonesia pushes this date back to 31,000 years ago! The team led by Tim Maloney from Griffith University that made this discovery suggests that this individual appears to have had their leg surgically amputated just above the ankle, and then proceeded to live for another 6-9 years based on bone remodeling around the amputation site. This evidence implies that modern humans had complex medical knowledge, such as how to locate and sever blood vessels, nerves, muscle tissue, and bone both safely and effectively, long before the advent of agriculture.
Yet, medicinal knowledge is not relegated to our own species! While animals like elephants, bears, and other apes have been known to ingest material for medicinal purposes, it was not until this year that a team led by Simone Pika from the University of Osnabrück observed apes using topical ointments for healing. After catching insects, the wild chimpanzees from the Rekambo community in Gabon, West Africa then squished them between their lips, rubbed the insect in the wound, and removed the insect afterwards. The truly groundbreaking part of the study announced in February is that the chimpanzees not only treated their own wounds, but wounds of each other as well. This sort of caring behavior was assumed to be reserved for our own species, but it seems like caring for others in one’s community could have deeper roots in our evolutionary history.
Another new study out in July led by Pascal Gagneux and Ajit Varki of the University of California San Diego looked at the intersection of medicine and genetics to explore why modern humans have developed such a long post-reproductive lifespan. The “grandmother hypothesis” posits that modern humans live well past sexual maturity in order to care for family members, specifically grandchildren. But when did this long lifespan evolve – and how? A specific gene that produces immune receptors (like specialized parts of immune system cells) called CD33 allows modern humans to prevent some side-effects of aging, specifically protecting the brain from inflammation and dementia. The gene for these CD33 receptors is not present in Neanderthals or Denisovans, meaning that it could be one advantage our species had over them, but it also means we had to have acquired it on our own rather than inheriting the gene from a common ancestor. One hypothesis this study explored comes from reproductive health: the idea that we evolved these receptors to fight gonorrhea bacteria. The bacterium coats itself in sugars to mimic the human body, and our version of the CD33 receptors can effectively fight it – sparing our reproductive health. This potentially indicates that this adaptation to reproductive health could have been co-opted by the human body to allow for longer lifespans. In other words, we evolved the CD33 receptors to fight gonorrhea, and as a result our bodies could fight against dementia and allow us to have grandparents!
Ancient DNA: A new Nobel Laureate
While there have been important strides made in genetics and human evolution in the past year, the most notable achievement must go to a new Nobel Laureate: Svante Pääbo! Born in Sweden in 1955, Pääbo has long been a leader in the field of aDNA, especially when it comes to humans and our closest relatives. In 2010, Pääbo’s team deciphered the Neanderthal genome, unlocking a whole new realm of anthropological insight. Pääbo has also been at the forefront of new discoveries in anthropology, including identifying the Denisovans and understanding the genetic relationships between Denisovans, Neanderthals, and our own species – as well as identifying the first early human Neanderthal-Denisovan hybrid. For these reasons and more, Pääbo was awarded the 2022 Nobel Prize in Physiology or Medicine rounding out 2022 with a fantastic close. Congratulations!
Edited by Jason Organ, PhD, Indiana University School of Medicine