How did the emergence of Homo sapiens affect ideas around death? What legacies have been passed down from ancient times? And can these give us insights into the origins of our current rituals around dying?
Possible answers to these questions could be derived from a new study in Nature, led by María Martinón-Torres of the National Research Center on Human Evolution in Burgos, Spain. It focuses on a two- to three-year-old child found buried in a Kenyan cave roughly 78,000 years ago. While this isn't the oldest burial grounds for Homo sapiens — to date, that is in Israel — this new discovery of a seemingly intentional burial offers insights into the evolution of how humans treated death.
The dearth of excavation sites in Africa has made studying ancient funerary practices difficult. The remains of this young child were discovered in a pit in the Panga ya Saidi cave site located in a tropical region of coastal Kenya. Taphonomic evidence, which examines the process of fossilization, suggested that the child was intentionally placed in a flexed position (sort of curled up like a ball) in the burial pit.
The burial of Mtoto
The original excavation of this pit took place in 2013. By 2017, archaeologists dug into Middle Stone Age (MSA) layers, uncovering the partial skeleton of the child. The poorly preserved bone fragments were plastered and transported for laboratory analysis, first to the National Museums of Kenya and then onto Burgos, where Martinón-Torres and her team began their work.
Besides the seemingly deliberate position of the body, the team noticed a few clues that suggested the child was swaddled in cloth, possibly with the intention of preserving the corpse. They also speculate the body was placed in a cave fissure — known as funerary caching — before being covered with sediment.
Plan view of the 2017 excavation next to a superimposed image of Mtoto to better depict the position of the child.Courtesy of Nature.
The child, who they named Mtoto, appears to have been intentionally buried. The authors reached this conclusion based on: the identification of a clearly dug pit; evidence that discriminates the burial fill from the surrounding layers; the completeness and integrity of the skeleton; the body's tightly flexed position; and the notable differences between the child's remains and the remains of animals in the same layer.
Other burial sites
Two earlier excavations in Taramsa, Egypt and Border Cave, South Africa were similar to the one in this Kenyan cave. However, the Panga ya Saidi remains appear to predate the Egyptian ones by 10,000 years and the South African ones by 4,000 years. Taken together, the team writes that these three digs reveal important insights in the funerary practices of our ancestors.
"The [Panga ya Saidi] child, in combination with the infant burial from Border Cave and the funerary caching of a juvenile at Taramsa, suggests that H. sapiens populations were intentionally preserving the corpses of young members of their groups between about 78 and 69 [thousand years]. Before 78 [thousand years], we know of no unambiguous burials of modern humans in Africa, despite the fact that earlier [Middle Stone Age] populations demonstrate sophisticated forms of symbolic expression."
The researchers are excited to have made headway on the cradle of civilization — a continent that rarely gives up its secrets. While researchers have discovered symbolic representations in Africa dating back at least 320,000 years, these new insights into death rituals are important for understanding the evolution of human consciousness, as well as how we view mortality.
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Stay in touch with Derek on Twitter and Facebook. His most recent book is "Hero's Dose: The Case For Psychedelics in Ritual and Therapy."
One of the oldest activities carried out by humans has been identified in a cave in South Africa. A team of geologists and archaeologists found evidence that our ancestors were making fire and tools in the Wonderwerk Cave in the country's Kalahari Desert some 1.8 million years ago.
A new study published in the journal Quaternary Science Reviews from researchers at the Hebrew University of Jerusalem and the University of Toronto proposes that Wonderwerk — which means "miracle" in Afrikaans — contains the oldest evidence of human activity discovered.
"We can now say with confidence that our human ancestors were making simple Oldowan stone tools inside the Wonderwerk Cave 1.8 million years ago," shared the study's lead author Professor Ron Shaar from Hebrew University.
Oldowan stone tools are the earliest type of tools that date as far back as 2.6 million years ago. An Oldowan tool, which was useful for chopping, was made by chipping flakes off of one stone by hitting it with another stone.
An Oldowan stone toolCredit: Wikimedia / Public domain
Professor Shaar explained that Wonderwerk is different from other ancient sites where tool shards have been found because it is a cave and not in the open air, where sample origins are harder to pinpoint and contamination is possible.
Studying the cave, the researchers were able to pinpoint the time over one million years ago when a shift from Oldowan tools to the earliest handaxes could be observed. Investigating deeper in the cave, the scientists also established that a purposeful use of fire could be dated to one million years back.
This is significant because examples of early fire use usually come from sites in the open air, where there is the possibility that they resulted from wildfires. The remnants of ancient fires in a cave — including burned bones, ash, and tools — contain clear clues as to their purpose.
To precisely date their discovery, the researchers relied on paleomagnetism and burial dating to measure magnetic signals from the remains hidden within a sedimentary rock layer that was 2.5 meters thick. Prehistoric clay particles that settled on the cave floor exhibit magnetization and can show the direction of the ancient earth's magnetic field. Knowing the dates of magnetic field reversals allowed the scientists to narrow down the date range of the cave layers.
The Kalahari desert Wonderwerk CaveCredit: Michael Chazan / Hebrew University of Jerusalem
Professor Ari Matmon of Hebrew University used another dating method to solidify their conclusions, focusing on isotopes within quartz particles in the sand that "have a built-in geological clock that starts ticking when they enter a cave." He elaborated that in their lab, the scientists were "able to measure the concentrations of specific isotopes in those particles and deduce how much time had passed since those grains of sand entered the cave."
Finding the exact dates of human activity in the Wonderwerk Cave could lead to a better understanding of human evolution in Africa as well as the way of life of our early ancestors.
For every great evolutionary innovation, there is a new way for things to go wrong.
Multicellularity allowed for more complex organisms, but those organisms became susceptible to cancer. The evolution of asymmetric cell division was a boon that prevented damaged cells from proliferating but also created the mechanisms which cause us to age. Blood cell traits that help prevent malaria can also cause sickle cell anemia. Improvements in our brain power can lead to mental illnesses that no other animal can get. In short, it seems that our own genetics can be both a blessing and a curse.
While this is interesting in and of itself, a team of researchers led by Dr. Mary Benton of Baylor University recently published an essay in Nature Reviews Genetics on the influence of evolutionary history on human health and disease and possible new approaches to treating ailments caused by our own genetics. Their essay considers how evolution accidentally made us susceptible to certain diseases and how genomics might be used to improve health outcomes.
No good idea goes unpunished
Credit: Benton et al.
As the above chart shows, evolutionary advances that impact our health occurred at various points in history. As the environment, both natural and social, changes, traits and adaptations that worked really well in the past can become a source of problems. Consider, for example, the tendency of humans to want sweet foods that were once rare. This was likely a useful trait to have when it evolved, but the surplus of sweets we have these days has resulted in an obesity epidemic. Outside of its original context, a once adaptive trait can become maladaptive.
Understanding the context within which certain traits entered the human genome can shed light on why they are now causing problems. This can yield further insights on population genetics and even personalized medicine. As the authors put it:
"Much like a family's medical history over generations, the genome is fundamentally a historical record. Decoding the evolution of the human genome provides valuable context for interpreting and modeling disease."
"While most of the variations that impact disease risk evolved recently, they are part of more complex systems that go much further back. With our improving understanding of how these variations interact with our modern environment, society, and cultures, doctors can potentially begin to use a patient's genetic history to help craft personal care plans."
An evolutionary understanding of disease
While evolutionary takes on disease are not currently used for most conditions, the capacity for medical professionals to do so is increasing. The authors mention the potential of polygenic risk scores, a recently developed technology that estimates the effect of a subject's genetics on their health, as a possible application of evolutionary history on individual health.
While not everyone can get a full genome record at this moment, the possibilities of using our evolutionary history in medicine are tremendous. Dr. Benton spoke to these possibilities with the Baylor University News Service:
"If we can better understand our genomes, then we can better understand risk for disease broadly, but also for specific people. Understanding how genetic variants relate to disease can help us tailor treatments, preventative measures, or drugs. Evolution plays into what variants we have, which variants have stuck around, which people they are present in, and why. I think evolution gives us context for what we want to use in the clinic moving forward."
Human childbirth is a relatively painful and complicated process in the animal kingdom.
Unlike other primates that are able to give birth unassisted, human mothers usually need help from their family or community to deliver a baby. Even with help, mothers and infants face a small chance of death during childbirth, especially in regions with limited access to healthcare, like Sub-Saharan Africa.
One reason human childbirth is dangerous is the "obstetrical dilemma." This dilemma describes what seems to be an anatomical contradiction: Human infants have large heads, but their mothers have small birth canals.
To pass through the birth canal, human infants have to perform a series of twists and turns, a process called rotational birth. (Human infants also have fontanels, commonly referred to as soft spots, which help them better squeeze through the birth canal.)
It begs the question: Why hasn't evolution made childbirth easier on humans?
Evolutionary trade-offs
A study recently published in Proceedings of the National Academy of Sciences proposes that human childbirth is difficult because of evolutionary trade-offs that ultimately help protect organs in the body.
The main trade-off for women centers on the pelvic floor, which is a group of muscles that stretches from the pubic bone to the tailbone. These muscles help stabilize the spine, support the womb, and control bladder and bowel functions. The pelvic floor also stretches during childbirth, allowing the baby to pass more easily through the birth canal.
A medical illustration depicting the female pelvic muscles.
A medical illustration depicting the female pelvic muscles.Credit: BruceBlaus via Wikipedia and licensed under CC BY-SA 4.0
Some researchers have proposed that a larger pelvic floor would make childbirth easier for women. But others have countered that a larger pelvic floor would actually be more vulnerable to deformation and could lead to disorders, including incontinence and organs dropping from their normal positions (known as prolapse).
Known as the "pelvic floor hypothesis," this idea has been difficult to test. In the current study, a team of researchers from the University of Texas and University of Vienna used computer models to test how increasing the size and thickness of the pelvic floor might affect women, both in general and during childbirth.
To test the models, the team used finite element analysis. This method, more commonly used in engineering projects, uses mathematics to test how structures would likely react to real-world forces, such as vibration, heat, fluid flow, and pressure. After testing a wide range of pelvic floor sizes and thicknesses, the results suggested that the pelvic floor hypothesis is correct.
"We found that thicker pelvic floors would require quite a bit higher intra-abdominal pressures than humans are capable of generating to stretch during childbirth," Nicole Grunstra, an affiliated researcher at the University of Vienna's Unit for Theoretical Biology in the Department of Evolutionary Biology, told UT News.
"Being unable to push the baby through a resistant pelvic floor would equally complicate childbirth, despite the extra space available in the birth canal, and so pelvic floor thickness appears to be another evolutionary 'compromise,' in addition to the size of the birth canal."
The results highlight how evolution has helped us achieve remarkable anatomical balance.
"Although this dimension has made childbirth more difficult, we have evolved to a point where the pelvic floor and canal can balance supporting internal organs while also facilitating childbirth and making it as easy as possible," lead study author Krishna Kumar told UT News.
Rabbits are, of course, adorable. We kvell over awww-inducing pictures of the little cuties who look like they couldn't hurt a fly. (Fun fact: Male rabbits are incredibly fierce when they fight each other and will actually fight to the death.)
Rabbits have been around for a long time, and they don't exhibit the same variations in size as for example, rodents. Even a big rabbit is not as big as, say, a capybara that can weigh from 60 to 200 pounds. Likewise, there is no rabbit anywhere near as tiny as a pigmy mouse of sub-Saharan Africa, which can weigh as little as 3 grams or as much as a zaftig 12 grams.
Researchers at Kyoto University's Primate Research Institute wondered why there are no horse-sized — or for that matter, tiny — lagomorphs. The lagomorph order includes rabbits, pikas, and hares.
The curious scientists recently published a paper titled "Why aren't rabbits and hares larger?" in the journal Evolution. It suggests the answer to this question may say something about the factors that most profoundly influence a species' evolution.
Size limited by competition
Credit: Victor Larracuente/Unsplash
First author Susumu Tomiya says, "The largest living wild lagomorphs weigh only about 5 kg on average, a tenth of the largest living rodent, the capybara."
There are breeds of domestic rabbits that can be somewhat large. Tomiya notes "some breeds of domestic rabbits and other extinct species can weigh up to 8 kg [about 17.63 pounds]. We were surprised by this, and so began to investigate what sort of external forces keep wild lagomorphs across the world from evolving larger body sizes."
After analyzing the available fossil record to explore how lagomorphs have fared through time, the team came to suspect that their size tended to be constrained by competition for food with larger herbivores.
Blame the sheep
As the researchers investigated the ecosystems in which lagomorphs lived, creatures of a different order, ungulates, came to their attention. Ungulates are an order of hoofed mammals including horses, rhinoceroses, and pigs. It also includes cloven-hoofed animals like cows and sheep.
It seems that ungulates were more than mere neighbors of rabbits, hares, and pikas. Similarly sized ungulates probably were their competitors.
The researchers calculated that large lagomorphs would require an excessive amount of energy — food, water and so on — to thrive, considerably more than smaller rabbits and hares. As a result, Tomiya says that when they compared "how much energy is used by populations of lagomorphs and ungulates relative to their body sizes," they found "that lagomorphs weighing more than six kilograms are energetically at a competitive disadvantage to ungulates of the same size."
To confirm their theory, the researchers next looked at the fossil record of North America. They found that the smallest hoofed animals predicted the size of the largest bunnies.
It remains true to this day, he says. "We see this pattern today across numerous eco-regions, suggesting that there is an evolutionary 'ceiling' placed on lagomorphs by their ungulate competitors."
The red queen versus the court jester
Tomiya says the study may help resolve biologists' ongoing "red queen" vs. "court jester" debate over the type of forces that most affect a species' evolution.
The red queen represents biotic forces and the court jester abiotic factors. ("Biotic" refers to other organisms that live in the same ecosystem as a species being studied, while "abiotic" refers to non-living factors such as climate, light, the quality of water, and so on.)
"For some time," says Tomiya, "the court jester model — ascribing diversity to abiotic forces such as the climate — has been dominant, due to the difficulty of studying biological interactions in the fossil record." He says the study's findings show that the red queen shouldn't be counted out when it comes to influencing evolution.
