Time Domains of Anthropogeny Seen Through the Field

James Yu

2023 Anthropogeny Field Course reflection written by James Yu, Anthropogeny Specialization Track Graduate Student (UC San Diego Department of Biomedical Sciences). Excerpted by CARTA staff.

For an anthropogenist, time is the enemy. We try and piece together the evidence of human origins and evolution that has occurred over millions of years, yet we’re physically constrained to the present. Our saving grace is that evolution leaves behind evidence – whether it be through bones, related species, DNA, human behavior, or current landscapes. For the CARTA fieldwork course, we sought to catch glimpses of human evolution in an immersive, interdisciplinary exposure that took us from the caves of Spain to the Rift Valley of East Africa. For this reflection, I will walk through the different time domains of anthropogeny that we explored throughout the course – not through the chronological timeline that we experienced, but rather through the timeline of human evolution that researchers have pieced together over the last several decades. Inevitably, many of these time domains overlap and are subject to change as more evidence emerges.

We begin in Mahale Mountains National Park. Humans and chimpanzees likely diverged on their evolutionary paths somewhere between [7-8] million years ago. Chimpanzees represent one of two closest living relatives to Homo sapiens, the other being bonobos. Due to our relatively recent evolutionary divergence, chimpanzees (through both their similarities and differences to humans) provide unique physiological, behavioral, and molecular insights into what makes humans human. At Mahale Mountains National Park, we had the opportunity to observe chimpanzees closely, in the wild, where they had presumably occupied the space for thousands of years.

We explored the park as tourists, with probably a little more collective primatology knowledge than the average group. The park sits on the eastern shore of Lake Tanganyika, the second largest freshwater lake in the world that remains a freshwater lake due to influx of rainwater from the surrounding rivers and streams. Mahale Mountains National Park has a long and rich history of chimpanzee research, with notable Japanese researchers from Kyoto such as Toshisada Nishida, who helped establish the chimpanzee research site in Mahale. MMNP is almost 50 times larger than Gombe Stream National Park, where Jane Goodall and colleagues have studied chimpanzees for just a little bit longer than the work at MMNP. It’s easy to see why the area was created into a national park in addition to its creation as a research site. The park is extremely lush and brimming with life. Despite the lack of motor vehicles, sound is constant from the abundant wildlife that is often hidden from view but ever-present.

…Observing…chimpanzees in their natural landscape begs the question of why humans would ever become bipedal on their independent evolutionary journey (there are several attempts at explaining bipedality, ranging for constraints imposed by vegetation such as tall grass, to energetics and metabolism, but we still lack a clear explanation for bipedality and it has also become increasingly clear that this type of locomotion might have evolved more than once!). These non-human primates moved much more efficiently than us humans in this thick, lush landscape, moving much quicker but also making much less noise. While there were clear differences between the chimpanzee group that were naturally foraging for food and our group with smartphones and cameras in hand, being this close to our primate cousins made it impossible not to anthropomorphize them – from a group of females with their babies “gossiping” and finally enjoying a peaceful moment with no aggressive males nearby, to peering into a youngling’s curious eyes and wondering what he thought of us naked apes. Yes, 5-7 million years is a long time for evolution to act, but in those moments of close interaction, I instantly felt the allure and promise of scientific answers that primate researchers must have seen when they first laid eyes on wild chimpanzees.

This allure first struck me when we were at Issa Valley, where we stayed at a chimpanzee research site run by Alexander Piel (UC San Diego PhD in biological anthropology) and Fiona Stewart (Cambridge PhD in primatology). Unlike the lush rainforests of Mahale, Issa Valley is a wooded, savannah called miombo woodland, at relatively high elevation 1550 m /~5000 feet habitat located in the Tongwe East Forest Reserve in western Tanzania. Although we spent time at Issa before Mahale, I place Issa after Mahale on this journey through evolutionary time because the mosaic savannah habitat of Issa is thought to be more representative of the landscape that hominins evolved in and therefore more likely to be similar to the environments where humans diverged from our most recent common ancestor with chimpanzees.

In Issa, we encountered chimpanzees for the first time on the trip. The landscape of Issa was very different than Mahale, with tall fields of grass abutting valleys of thick riparian, evergreen forests. Despite these differences and the openness of the landscape, it was once again incredible to see how efficiently the chimpanzees moved, especially in comparison to us humans that tried to follow them. Due to the nature of the mosaic landscape mixed between plateaus with grasslands and miombo woodlands, Issa contains steep valleys that go down to the network of rivers that flow in between hills and mountains. The chimpanzees cross up and down these valleys with ease, gracefully moving through the grasslands, steep embankments, and thick forests on all four limbs. Similar to Mahale, it was difficult to imagine why hominins may have become bipedal in this environment in the first place, due to how much more nimbly our primate cousins moved than us. This observation is supported by researchers at Issa Valley that witnessed bipedality of chimpanzees within the trees, hinting that bipedality may have actually evolved in an arboreal context rather than a terrestrial one. Importantly, bipedal posture in trees is a far cry from striding bipedalism with the many adaptations in feet, ankles, knees, pelvis and the entire spine.

Of even starker contrast between the Issa and Mahale landscapes was the abundant evidence of regular fires in Issa Valley. Mosaic savannah environments rely on regular fires to maintain its landscape structure; this is reflected in the local vegetation that is fire-adapted along with the animal species that have evolved to occupy these environments. This was made very obvious when we walked through different areas of Issa that were in various stages of recovery from fires of both natural and human made origin. Unlike the deeply forested sections of Issa, freshly burnt areas were extremely easy to move through and allowed one to see much farther throughout the environment – of obvious impact to predation for species that rely highly on visual stimuli. Areas that have had some time since burning were full of new life poking through the burnt ground, allowing for rich variability in plant life and thus creating novel niches within the ecological system. Natural fires have likely affected this region and many others like it within Africa long before humans ever “domesticated” fire, which begs the question, if hominins did indeed evolve in a mosaic savannah landscape, did they also learn to opportunistically use fire in these landscapes as well?

…Next in our journey through evolutionary time, we encountered the East African Rift Valley and the shores of Lake Manyara, where we moved on from our ancestral cousins and world of comparative research to focus on the environments that hominins evolved in. The rift was created and has been continually shaped by tectonic plate movements for millions of years, and is still changing today due to these movements, resulting in diverse sets of landscapes, climates, and geological features. This includes alkaline lakes, which are rare throughout the world but more abundant in the rift valley due to unique geological characteristics such as volcanic activity and limited influx of freshwater from rivers and streams. Many portions of the rift valley are also ecotones, which are transition areas between two distinct ecosystems, including the shores of Lake Manyara, which we drove by on our way from Arusha to Ngorongoro Crater. Such ecotones are known to be hotspots of biological diversity which also makes them unusually rich in exploitable resources for a newly bipedal hominin.

This drive was punctuated with stops that pointed out certain geological features and commentary about how these variable environments most likely provided strong evolutionary pressures on hominins. The vast majority of species become extinct; humans almost became extinct on multiple occasions, but now occupy every continent and have the widest range of habitation of any species in the world. One of the ways in which humans have been able to accomplish this was hinted at throughout our drive – humans, and most likely our hominin ancestors, are highly adaptable. Therefore, the hominins that occupied these environments and ecotones within the Rift Valley, such as the famous Lucy, most likely benefited from the diverse set of landscapes that offered different nutritional resources throughout changing seasons and climates. Humans may be much weaker and less able to climb trees than our ancestral cousins such as the chimpanzees, but there is a reason why humans can travel from one continent to any other within a day and create vaccines that target specific viruses, a feat unaccomplished by any other species on the planet.

Our next stop on this drive through northern Tanzania, and conveniently the next time domain of our journey through human evolution, was Ngorongoro Crater and Conservation Area. Ngorongoro Crater is believed to have formed approximately 2.5 million years ago when a massive volcanic eruption created a caldera after collapsing in on itself. It is the largest unbroken caldera in the world and contains an extremely diverse and abundant group of wildlife, making it extremely unique with no counterpart to it outside Africa. This uniqueness and abundance of life also makes it a critical location for conservation and ecological research, earning the designation of a UNESCO World Heritage Site and protection against hunting.

This protection and conservation status is crucial for many researchers encompassing different areas and also for hunter-gatherers (discussed later), but it is also beneficial for anthropogenists because Ngorongoro Crater provides a snapshot of an environment that hominins may have evolved in, providing remarkable insights into human evolution. It was staggering to see just how rich in life this area was as we drove through in a Safari vehicle. I expected that we would have to “hunt” to see these animals from afar, but they were abundant throughout the area and at times in high density, clearly habituated to the large, noisy vehicles that would drive up close to them. An additional surprise was how often “friends and foes” (predators and prey) were in proximity to one another, simply resting. This observation reinforced the notion that for most species on earth, and for most of their evolutionary time history, life is a matter of energy balance – living beings obtain energy in order to pass on genetic information to offspring while pursuing behavior that optimizes energy usage. Oftentimes, the chase isn’t worth it, and it’s only worth it when you need to consume food for energy.

2023 Anthropogeny Field Course Group at Ngorogoro Crater

2023 Anthropogeny Field Course Group at Ngorogoro Crater

Our experience in Ngorongoro Crater also sparked thoughts on implications of hominins hunting and being hunted. Humans most likely began eating meat regularly around 2 million years ago, as evidenced by archaeological remains of tool use and butchery. Humans evolved in this clear abundance of potential meat, but seeing some of these larger herbivores such as zebras, wildebeests, and buffalo made me question whether hominins were the prolific hunters portrayed by some researchers, or rather if they primarily started off and became scavengers of meat. In addition, seeing large predators such as lions, spotted hyenas, leopards and servals (not to forget the large crocodiles in any body of water, and the very aggressive hippos) emphasized that hominins also evolved in this environment as potential prey and a source of meat themselves. Knowing that hominins may not have developed controlled use of fire before one million years ago, they may have very well been at the mercy of some of these predators, perhaps finding protection in larger numbers of bands or tribes and seemingly larger vertical size due to their upright posture (though this does not deter lions from killing giraffes, which we were viscerally reminded of during our day in Ngorongoro crater when we chanced upon a family of lions gorging themselves).

Leaving the lush life of Ngorongoro, we next find ourselves in Olduvai Gorge. Although Olduvai is dusty and dry in our current times, the landscape at Olduvai was most likely lush and ever-changing with powerful river systems that created the gorge over millions of years. As we looked down into the massive gorge from an elevated viewpoint, a guide provided some historical knowledge about the gorge. The name of Olduvai Gorge was actually created due to a misunderstanding of the scientist Wilhelm Kattwinkel when he asked the Maasai people the name of the gorge and they believed he was asking for the name of the East African wild sisal, otherwise known as oldupai; he misheard and called the gorge Olduvai Gorge, a name that has been a staple in the world of human evolution.

I place Olduvai Gorge next in our evolutionary journey after the Ngorongoro Crater because four different hominin remains were found here and their timespans range from approximately 2 million years ago to much more recently at approximately 17,000 years ago. These include Paranthropus boisei, whose remains were found by Mary Leakey while she was out for a walk while Louis Leakey was sick in bed with a fever; Homo habilis, potentially an early tool-user; Homo erectus, potentially the longest-surviving hominin, and Homo sapiens, the hominin that has undoubtedly changed the world the most. Evidence of meat-eating and mammal butchery overlaps with some of the timespans that these hominins occupied, raising the same questions that arose while we were in Ngorongoro Crater as to whether humans primarily hunted or scavenged to attain meat in their earliest days. Although we didn’t have the opportunity to walk into the gorge, it was incredible to see it from above, knowing that many of the crucial archaeological findings and clues to our evolutionary past were discovered right there, within that dry and dusty gorge.

We leave the dust behind to next encounter the Serengeti and Ndutu Lake. The Serengeti contains multiple different ecosystems that provide a home to an incredible biomass of herbivores. One of the primary ecosystems are the volcanic grasslands, formed over millions of years of eruptions (resulting in a vast flat area, where the volcanic dust created a hard pan preventing most trees to form roots, but allowing a large number of grass species to thrive seasonally driven by two yearly wet seasons), but most notably by a more recent eruption by the volcano Kerimasi approximately 150,000 years ago, thereby placing it after the Olduvai Gorge on our evolutionary journey. These eruptions created a hardened layer below shallow soil that trees are unable to break through with their roots, hence the domination of tall grasslands throughout these environments. In turn, these grasslands support the largest group of mammals in the world, including the great migration of the wildebeests, which occurs every year between January and March and contains approximately 500,000 wildebeest babies.

During our visit to this rich network of ecosystems, we encountered a diverse set of wildlife which sparked ideas of which animals our hominin ancestors must have relied on for survival. This inevitably included the large herbivores that must have provided a consistent and abundant source of nutrient-rich food. But these encounters also sparked insights into other key animals that may not be so obvious, such as ostriches – their eggs may have provided a rich source of nutrients for early hominins but may have also served as a portable container once emptied out, allowing early humans to transport liquids. Another insight were the predators; these lions, leopards, spotted hyenas, and others most likely dined on hominins in our early ancestral days. This predatory pressure may have pushed humans to develop defensive strategies such as moving and living in a group, thus creating the first tribes. If this pattern of behavior resulted in more offspring, group cooperation may have been a strong evolutionary pressure.

As we explored the Serengeti, our intrepid and insightful guide, Douglas Simbeye, had us get out of the vehicles and stand in a circle, facing outwards. On his mark, we ran for a bit, each in our own direction, until he instructed us to stop. From here, we either sat or stood in silence, observing the world around us in our own solitary bubble. Standing there and peering out into the vast grasslands in front of me, I envisioned what it must have been like for our early human ancestors – how they must have been able to look out for miles to search for prey and predator alike, standing above the tall grass on their two legs instead of on all fours like many of the other animals; how it must have been brutally oppressive in the peaks of heat throughout the day, and chillingly cold during the night; how uneventful it must have been to see some of the animals that we were amazed by. Having just run for a bit to get to my current position, I also thought about how modern humans are the best long-distance runners on the planet, beating out horses, dogs, and cheetahs. This incredible feat potentially allowed earlier humans to be persistence hunters, where they would chase down an animal repeatedly until it is run to exhaustion, a physically demanding but potentially effective method of hunting an animal that is otherwise a faster runner than humans.

For our next time domain of human evolution seen throughout the fieldwork course, we leave the continent of Africa just like our human ancestors and enter Europe, where we encounter the Atapuerca Mountains of northern Spain. Atapuerca is one of the most prolific archaeological and paleontological sites in the world; it encompasses multiple cave and sinkhole sites and has been crucial for shedding light onto human evolutionary history as hominins expanded out of Africa and occupied the rest of the world. Ancient remains require very specific ambient conditions in order to stay preserved enough for analysis, and most geographical portions of Europe are not conducive to these particular set of conditions. Atapuerca is unique in its geological systems that have provided ideal environmental conditions for remains to stay preserved and accumulate over time, providing a robust set of evidence for human (and other animal) occupation.

We were luckily able to get a behind-the-scenes glimpse into Atapuerca, interacting with researchers that were currently there digging, cataloguing, and analyzing precious finds in some of the famous sites such as the Sima del Elefante, Gran Dolina (where Homo antecessor was first found), and Galería. We were exposed to both the archaeological and paleontological purpose behind Atapuerca’s hum of research (archaeology focuses primarily on human history and culture while paleontology focuses on all prehistoric life) and saw firsthand how these sites were explored in an extremely methodological manner to ensure proper logging and analysis of findings. First, the researchers would date the layers by getting a “core” of dirt; the dating method varies by timespan and environment, but they include magnetic dating, which relies on changes in the Earth’s magnetic field over time, radiation dating, which relies on accumulated radiation exposure to estimate an age, and many others. Then, the researchers mark the various layers and label them throughout the site. They then go through each layer – the less interesting layers get tossed into a dumpster while the more interesting layers are placed into buckets that are methodically dated and labeled with where the dirt came from. If they encounter an interesting, larger find during this time (such as the hippopotamus foot we witnessed less than 2 feet away from a rhinoceros mandible that was being stabilized prior to extraction from the sediment bed), they will very meticulously excavate the finding with chisels and brushes. The buckets are then sifted and washed using the nearby river, where other researchers pore through the fragments that remain. Once washed, they are transported to the laboratory where they are further cleaned and examined. All findings are then methodically labeled and catalogued using an integrated digital system.

The work is physical, grueling, and extremely tedious. The whole process requires a massive operation with hundreds of researchers. These researchers congregate every summer to carry out this operation within an intense period of focused effort, hailing from different parts of Europe. We were fortunate enough to be there during this time and witnessed old friends from different universities work early in the morning to late in the evening, with communal work broken up by breaks of tapas, beer, and conversation. I was touched to learn that many of the findings of the current day would not be analyzed by those researchers, but likely down the road by someone else – a form of “paying it forward” in this multi-country, multi-institute network of archaeologists and paleontologists.

…Our last stop is Hadzaland, home of the Hadza hunter-gatherers between Lake Eyasi and Yaeda Valley. Here, many of the facets related to human evolution that we’ve seen so far converge. Hadzaland lies in east Africa in the northern part of Tanzania and is in proximity to many of the locations discussed earlier (Olduvai Gorge is only 50 kilometers to the northwest), inferring that Hadza live in land where many of our human ancestors once lived. The Eyasi hominin fossils dated at over 80ky were found in a cave very near Maji Moto, where we stopped for a picnic and explored boulders where the desert rose plant grows that provide the cardiac glycoside arrow poison used to great effect by the Hadza. Although it is hard to date how long they have lived in this land due to their history being documented via oral traditions, the Hadza have most likely lived in the general vicinity of where they are now for their whole history, which is most likely thousands of years. Genetic studies indicate that the Hadza have maintained a distinct lineage from other click-speaking populations in Africa for at least 15,000 years and comparisons with other African groups yielded the greatest divergence between two populations ever tested, which provide some of the most robust evidence for the out-of-Africa model of modern human dispersal. The Hadza provide an amazing opportunity to peer into human evolution because they have maintained a similar way of life for the duration of their history, providing a unique perspective into what makes humans human…

…There were many more health implications that were evident when observing how different modern societal lifestyle is from the Hadza lifestyle and all of these can be summarized as examples of evolutionary mismatch, where there is a mismatch between the environments we evolved in and the ones we live in today, resulting in health impacts. My time with the Hadza certainly accentuated my awareness of evolutionary mismatch and throughout our time together, I constantly thought about how differences in our lifestyle may contribute to diseases that are at a much higher frequency within modern societies. These ranged from non-communicable diseases, the number one killer in “modernized” countries, to less severe mismatches, such as visual acuity and foot morphology and general lack of flexibility and motility in adults from western countries. None of the Hadza wore glasses and it seemed none of them needed glasses. In the bush, visual acuity is paramount and required for hunting, foraging, and identifying potential threats. The Hadza do not read, stare at screens from a close distance regularly, or stay within buildings with small rooms all day, perhaps contributing to their lack of visual issues. If they do wear shoes, they’re often sandals that do not inhibit the natural splay of the toes, in direct contrast to most modern shoes that have a constricted toe-box that fundamentally change the morphology of our feet (although we did see some Hadza individuals sporting fashionable modern sneakers, undoubtedly prized possessions). All of these factors potentially contribute to the divergent health we see between the Hadza and modern societies, and interacting with the Hadza certainly now pushes me to live my life more in line with our evolutionary history.

After spending time with the Hadza, it is impossible not to admire them. Here are humans, our brothers and sisters, that have held onto their traditional way of life for thousands of years, passing on knowledge orally throughout the generations. … On our last full day with the Hadza, they asked us why we had traveled from the other end of the world to sit with them and observe them. They were touched that we’d simply just be curious about their way of life. When we asked if there was anything they wanted us to relay to the world on their behalf, they replied, “We are Hadza, this is how we live. Tell the world about us.” And that is part of the purpose of what I have written here.

At the end of this whirlwind of a trip, the question remains: what makes us human? As we’ve seen here and learned from previous CARTA interactions, the answer can be infinitely complex, ranging from bipedalism, bigger brains, blushing, language, and controlled use of fire to our incredibly frightening ability to permanently change the face of the world in a short period of time. But after experiencing this amazingly immersive fieldwork course, the answer can also be just as infinitely simple – being human is sitting around a campfire, chatting about the day, dreaming of the future, gossiping about other groups, and occasionally looking up at the stars to wonder who or what must have created all this. Time may be the enemy of the anthropogenist, but a fieldwork course such as this remains timeless, as these experiences have fundamentally shaped how I view human evolution and will continue to do so for the rest of my life.