Climate changes influencing hominin diversity
What evolutionary pressures were most influencing in causing hominin diversity to come about? The current evidence is that climate changes may have played a large role in shaping human evolution, and also competition between hominins. By and large over the period we are considering, there is a trend towards cooler and drier conditions, but within that trend, the climate oscillates at predictable intervals, so at times it will be hotter and wetter and at other times cooler and drier. So diet and locomotion that works at one time may not be so successful in another.
Major shifts in African climate change coincide with two moments on that ancestral path roughly a million years apart, marking significant changes in our family tree. It is thought by some scientists that two episodes of climate change may have been responsible for these evolutionary milestones so clustered in time These two major ecological jolts, coming after long periods of gradual change, may have been responsible, moving the cradle of humanity towards increasingly dry and open grasslands.
Meanwhile, the climate alternated rapidly between wet and dry periods, so to thrive, our ancestors had to adapt to rapidly changing landscapes. The disappearance of a favourite food or the replacement of a long wet season with a longer dry one, create pressures that lead, eventually, to adaptation, extinction or evolution into different species. According to Darwinian theory, over time those creatures who emerge with advantageous traits such as large brains and the genes they carry will come to dominate because more of them will survive.
The first of these shifts occurred between 2.9 and 2.4 Mya, when the ancestral line of “Lucy” (A. afarensis) became extinct, and two other quite distinctive groups appeared. . One of them had hints of some modern looking traits, including larger brains. They were the very first members of our genus Homo. The first stone tools appeared near these fossils. The other group which appeared at this time looked different: the stoutly built and heavy-jawed Paranthropus. During this period, changes in carbon isotope ratios from land and ocean sediments show dry grasslands rapidly expanded and wetter woodlands shrank.
Then between 1.9 and 1.6 Mya, an even larger-brained and more carnivorous species, H. erectus, also known as H. ergaster by some scientists, appeared on the scene with a taller, more lithe skeleton, nearly indistinguishable from modern humans. This species was the first to leave Africa to populate Southeast Asia and Europe. They lived in the Middle East and Far East including Java. Stone Age technology also got a major upgrade: the first axes showed up, with large blades carefully shaped on two sides. During this period, the carbon evidence shows grasslands got another boost. Yet carbon in the teeth from H. erectus indicates the consumption of a mixed diet and an ability to find food from a variety of sources, even as grassland enlarged. Paranthropus teeth, however, showed the group (like an earlier extinct forbear, Kenyanthropus), was restricted to eating from grassy surroundings. As a result, it became extinct.
Dawkins familiarly refers to this species as ergasts rather than 'erects' - Homo ergaster stemming from the African line - partially because “I believe that” the majority of our genes trace back to the African form, and partially because the species were no more erect than their predecessors (H. habilis) or successors – us. They persisted in Eurasia and Africa from about 1.8 million to about a quarter of a million years ago.
"They walked on two legs like us, but had smaller brains (averaging perhaps 800cc in early specimens and over 1000cc in late ones), housed in lower, less domed, more ‘swept-back’ skulls than ours, and they had receding skills. Their jutting brow ridges made a pronounced horizontal ledge above the eyes, set in wide faces, with a pinching in of the skull behind the eyes”. [1]
[1] Richard Dawkins and Yan Wong, The Ancestor's Tale - A Pilgrimage to the Dawn of Life, Weidenfeld Nicolson, London, 2004, 2nd edition, 2016, 81.
What was the evidence for these climatic changes?
1. Silt from the ocean floor
Peter B. deMonocal describes the process of drilling cores for ocean sediments nearly half a mile into the sea bottom in a mile and a half of water in the Arabian Sea. By drilling into the seafloor off the African coasts, geologists have been able to penetrate a multimillion year time capsule, recovering long cores of sediments that preserve complete records of past African environments. Since the divergence of great ape and human lineages several million years ago, the ocean bottom in the Arabian Sea had accumulated nearly 1000 feet of deep-sea mud at a rate of about 1 ½ inches every 1000 years. The sediments here consist of mixtures of fin-white calcium carbonate fossil shells from ancient ocean plankton and darker, silty grains of dirt blown from areas of Africa and Arabia by windy monsoons. When the mix looks darker and gritty, it indicates drier, dustier times. When it looks lighter, that reflects wetter, more humid conditions. The research indicated that the alternating light and dark layers repeated about every three feet, which meant that they changed about every 23,000 years, in tune with the earth’s wobble, which changes the amount of sunlight hitting our planet in a given season, illustrating the fact that African climate change history had been one of continuous swings between wetter and drier times. For North Africa and South Asia, more or less heat during summer increased or decreased monsoon rainfall, making these regions either wetter or drier as our planet wobbled back and forth.
Research techniques:
2. Photosynthetic studies of grasslands
Superimposed on these orbital wet-dry cycles were larger steps toward dry and open grasslands, and just about this time, our evolutionary history received a jolt when, as we have seen, just under 3 Mya we lost Lucy (the species Australopithecus afarensis). Next the paranthropus group appeared, followed 2.6 Mya by the first signs of stone choppers and scrapers and then in a few hundred thousand years by the early Homo fossils. We know these changes in our family tree and in technological invention occurred because we have been able to trace the “fingerprints” left by some plants that flourished in wetter environments and others that thrived in drier times.
Savannah grasses do very well in hot, dry regions because to take up carbon from the atmosphere. They use a specific photosynthetic pathway called C4 – miserly with carbon and water, an adaptation to life in dry and low-CO2 environments. Woody vegetation such as trees finds homes in wetter ecosystems because it uses another photosynthetic pathway called C3 which requires much more water. C4 grasses have a greater abundance of the heavier but rarer carbon 13 isotope relative to the lighter, more abundant carbon 12 isotope. C3 shrubs and woody plants have a lower carbon 13/12 ratio, and scientists can take samples of soil or nodules of rock from a given landscape , analyse the catbon ratios and use them to accurately estimate the percentage of C4 grasses to C3 woody plants that were once in that area.
The East African landscapes from sites that had yielded fossil hominins revealed that before 8 Mya, they were predominantly C3 forests and shrublands. After that the proportion of C4 grasslands increased gradually. Then a relatively large and fast shift occurred between 3 and 2 Mya when grasslands expanded rapidly across present day Kenya, Ethiopia and Tanzania. This was accompanied by a rise in the proportion of grazing mammals, as revealed by their abundant fossils. The two largest of these events occurred between 2.8 and 1.8 Mya. Prehistoric diet changes seem to be part of this second evolutionary movement in our history nearly two Mya when Homo fossils that looked more modern first appeared. In the case of the Turkana Bay fossils, a dietary split occurred between member of our own Homo genus and members of the heavy jawed Parathropus group, at just under the 2 Mya mark. The carbon isotope tooth data from Parathropus boisei (“Nutctacker Man”) indicates that it ate a narrow mostly C4 based diet, though not by cracking nuts, but eating soft C4 grasses and sedges.
However, early Homo teeth indicated a strikingly mixed roughly 65-35 diet of C3 and C4 based foods, revealing that Homo sought diverse foods from a landscape that was increasingly uniform. “Early Homo had a varied, flexible diet and passed its genes to subsequent lineages, eventually leading to us. Paranthropus, in contrast, lived in a narrow C4 dietary niche and eventually became extinct”.
1. Silt from the ocean floor
Peter B. deMonocal describes the process of drilling cores for ocean sediments nearly half a mile into the sea bottom in a mile and a half of water in the Arabian Sea. By drilling into the seafloor off the African coasts, geologists have been able to penetrate a multimillion year time capsule, recovering long cores of sediments that preserve complete records of past African environments. Since the divergence of great ape and human lineages several million years ago, the ocean bottom in the Arabian Sea had accumulated nearly 1000 feet of deep-sea mud at a rate of about 1 ½ inches every 1000 years. The sediments here consist of mixtures of fin-white calcium carbonate fossil shells from ancient ocean plankton and darker, silty grains of dirt blown from areas of Africa and Arabia by windy monsoons. When the mix looks darker and gritty, it indicates drier, dustier times. When it looks lighter, that reflects wetter, more humid conditions. The research indicated that the alternating light and dark layers repeated about every three feet, which meant that they changed about every 23,000 years, in tune with the earth’s wobble, which changes the amount of sunlight hitting our planet in a given season, illustrating the fact that African climate change history had been one of continuous swings between wetter and drier times. For North Africa and South Asia, more or less heat during summer increased or decreased monsoon rainfall, making these regions either wetter or drier as our planet wobbled back and forth.
Research techniques:
2. Photosynthetic studies of grasslands
Superimposed on these orbital wet-dry cycles were larger steps toward dry and open grasslands, and just about this time, our evolutionary history received a jolt when, as we have seen, just under 3 Mya we lost Lucy (the species Australopithecus afarensis). Next the paranthropus group appeared, followed 2.6 Mya by the first signs of stone choppers and scrapers and then in a few hundred thousand years by the early Homo fossils. We know these changes in our family tree and in technological invention occurred because we have been able to trace the “fingerprints” left by some plants that flourished in wetter environments and others that thrived in drier times.
Savannah grasses do very well in hot, dry regions because to take up carbon from the atmosphere. They use a specific photosynthetic pathway called C4 – miserly with carbon and water, an adaptation to life in dry and low-CO2 environments. Woody vegetation such as trees finds homes in wetter ecosystems because it uses another photosynthetic pathway called C3 which requires much more water. C4 grasses have a greater abundance of the heavier but rarer carbon 13 isotope relative to the lighter, more abundant carbon 12 isotope. C3 shrubs and woody plants have a lower carbon 13/12 ratio, and scientists can take samples of soil or nodules of rock from a given landscape , analyse the catbon ratios and use them to accurately estimate the percentage of C4 grasses to C3 woody plants that were once in that area.
The East African landscapes from sites that had yielded fossil hominins revealed that before 8 Mya, they were predominantly C3 forests and shrublands. After that the proportion of C4 grasslands increased gradually. Then a relatively large and fast shift occurred between 3 and 2 Mya when grasslands expanded rapidly across present day Kenya, Ethiopia and Tanzania. This was accompanied by a rise in the proportion of grazing mammals, as revealed by their abundant fossils. The two largest of these events occurred between 2.8 and 1.8 Mya. Prehistoric diet changes seem to be part of this second evolutionary movement in our history nearly two Mya when Homo fossils that looked more modern first appeared. In the case of the Turkana Bay fossils, a dietary split occurred between member of our own Homo genus and members of the heavy jawed Parathropus group, at just under the 2 Mya mark. The carbon isotope tooth data from Parathropus boisei (“Nutctacker Man”) indicates that it ate a narrow mostly C4 based diet, though not by cracking nuts, but eating soft C4 grasses and sedges.
However, early Homo teeth indicated a strikingly mixed roughly 65-35 diet of C3 and C4 based foods, revealing that Homo sought diverse foods from a landscape that was increasingly uniform. “Early Homo had a varied, flexible diet and passed its genes to subsequent lineages, eventually leading to us. Paranthropus, in contrast, lived in a narrow C4 dietary niche and eventually became extinct”.
On the subject of climate change and diversity, see the conclusion to Stephen Brusatte's, "What killed the dinosaurs", Scientific American, December 2015, 46 at 51, noted in The Cretaceous Paleogene boundary" at /the-cretaceous-paleogene-boundary.html
Summary
The research indicates a series of rapid climate cycles and two large shifts that established the African savannah we know today, and that some of our most successful forebears had the flexibility to adapt to these changes. Those that could not or did not adapt became extinct.
It should be noted that each of the “big five” mass extinctions over the fossil record of life on earth during the past 540 million years was accompanied by an environmental disruption. During each of these events, between 50 and 90% of all species perished, but this was followed by bursts of new, very different species. For example, after a Manhattan sized meteorite struck the Yucatan peninsula about 66 Mya, it killed off the dinosaurs and many other species, ushering in the rapid radiation and diversification of mammals, one group of which led eventually to us.
Another factor - competition between hominins
Another pressure favouring hominin diversity may have been competition between hominins. If two hominins shared a habitat, they would have tended to force each other into different survival strategies. This may explain how H.habilis and P boisei came to have such different teeth and jaws – with one group favouring tough, fibrous foods such as grasses and the other leaning towards a diet that included softer but harder to find fruits plus the occasional meal of meat or bone marrow.
Wood predicts that the increased hominin diversity that has been identified in the last four million years will be shown to extend back even further. So, the closer one gets to the split between the human and the chimpanzee–plus-bonobo lineages, the more difficult it will be to tell a direct human ancestor from a close relative. In other words, rather than looking like a tree, rather does “(o)ur early ancestry looks more like a bundle of twigs – one might even think .. a tangled bush”[1].
Another view – we have identified too many species
Another and more recent view suggests that all these so-called distinctions between erectus, habilis and rudolfensis may be exaggerated, and that they may all be part of the same species with different skull shapes, much the same as humans have[2]. In other words, the human family tree may have fewer branches than at first thought. Five skulls recently found at Dmanisi in Georgia from a period 1.8 million years ago all with different skull shapes suggest as much, according to Professor David Lordkipanidze, an anthropologist at the Georgian National Museum at Tbilisi. One of the skulls had a small brain case, a long face and large teeth, features never before seen together. Its location with other contemporary skulls allowed the researchers to compare them. The brain case of this specimen measured only 546 cc, whereas modern humans have an average brain volume of about 1250 cc. Given that the population of individuals showed no greater range of variation than that of five human or bonobos, the researchers proposed that early Homo individuals may not represent three species, but one.
Others in the field are sceptical of such claims. Whilst not disputing that the five skulls at Dmanisi may have come from the same species, they reject the wider generalisation, pointing out that the reason why Homo habilis and Homo erectus are viewed as distinct is not just the cranial shape, but also changes in the wrists and ankles, as well as in the leg bones which took place at about that time. So merging the classes does not make sense, even if they share cranial shapes. In other words, the finding is unlikely to change experts’ views on species diversity.
On the other hand, there may even be more species within the human family: dating methodology
Dating and the revision of the molecular clock method – the old method
Until relatively recently, the conventional view of human evolution, culminating in the emergence of our own species Homo sapiens, was a story of survival and extinction that took place over 6 million years. This was based on what is known as the molecular clock method in conjunction with the fossil record,
DNA analysis measured in terms of mutations
As two species diverge from a common ancestor, their DNA becomes increasingly different, largely due to the accumulation of random mutations. Geneticists use DNA to assist in tracing events in a species’ past including information about their common ancestry and speciation. The amount of genetic difference between two related species is therefore proportional to the length of time since they diverged. To estimate when the divide between humans and chimpanzees occurred, for example, geneticists simply count the differences in matching stretches of chimp and human DNA and divide it by the rate at which mutations accumulate. This “molecular clock method” came up with a baseline of 4 to 6 million years ago when the human-chimp split is said to have occurred, but paleontologists considered this date as unduly conservative – in other words, they said the split had to have been older than that.
So are there more species within the human family?
The crucial factor is the rate at which these genetic mutations have been occurring, and recent research has tended to suggest that the molecular clock ticks more slowly than had previously been thought, pushing the human-chimp split further back in time[3]. This new research tends to suggest that the human lineage went its separate way at least 7 and possibly as far as 13 Mya. The result is that the fossil discoveries of Ardipithecus ramidus (‘Ardi’), a 4.4 million year old fossil from Afar, Ethiopia, Sahelanthropus tchadensis (6 to 7 Mya) and Orrorin tugensis (c 6 Mya) - all found during a burst of palaeoanthropologist discovery during the late 1990s and early 2000s and referred to below - were once thought to be outside the pale of humankind, even though they all had distinctly human characteristics. Under the new regime, they now emerge as possible human ancestors:
The research indicates a series of rapid climate cycles and two large shifts that established the African savannah we know today, and that some of our most successful forebears had the flexibility to adapt to these changes. Those that could not or did not adapt became extinct.
It should be noted that each of the “big five” mass extinctions over the fossil record of life on earth during the past 540 million years was accompanied by an environmental disruption. During each of these events, between 50 and 90% of all species perished, but this was followed by bursts of new, very different species. For example, after a Manhattan sized meteorite struck the Yucatan peninsula about 66 Mya, it killed off the dinosaurs and many other species, ushering in the rapid radiation and diversification of mammals, one group of which led eventually to us.
Another factor - competition between hominins
Another pressure favouring hominin diversity may have been competition between hominins. If two hominins shared a habitat, they would have tended to force each other into different survival strategies. This may explain how H.habilis and P boisei came to have such different teeth and jaws – with one group favouring tough, fibrous foods such as grasses and the other leaning towards a diet that included softer but harder to find fruits plus the occasional meal of meat or bone marrow.
Wood predicts that the increased hominin diversity that has been identified in the last four million years will be shown to extend back even further. So, the closer one gets to the split between the human and the chimpanzee–plus-bonobo lineages, the more difficult it will be to tell a direct human ancestor from a close relative. In other words, rather than looking like a tree, rather does “(o)ur early ancestry looks more like a bundle of twigs – one might even think .. a tangled bush”[1].
Another view – we have identified too many species
Another and more recent view suggests that all these so-called distinctions between erectus, habilis and rudolfensis may be exaggerated, and that they may all be part of the same species with different skull shapes, much the same as humans have[2]. In other words, the human family tree may have fewer branches than at first thought. Five skulls recently found at Dmanisi in Georgia from a period 1.8 million years ago all with different skull shapes suggest as much, according to Professor David Lordkipanidze, an anthropologist at the Georgian National Museum at Tbilisi. One of the skulls had a small brain case, a long face and large teeth, features never before seen together. Its location with other contemporary skulls allowed the researchers to compare them. The brain case of this specimen measured only 546 cc, whereas modern humans have an average brain volume of about 1250 cc. Given that the population of individuals showed no greater range of variation than that of five human or bonobos, the researchers proposed that early Homo individuals may not represent three species, but one.
Others in the field are sceptical of such claims. Whilst not disputing that the five skulls at Dmanisi may have come from the same species, they reject the wider generalisation, pointing out that the reason why Homo habilis and Homo erectus are viewed as distinct is not just the cranial shape, but also changes in the wrists and ankles, as well as in the leg bones which took place at about that time. So merging the classes does not make sense, even if they share cranial shapes. In other words, the finding is unlikely to change experts’ views on species diversity.
On the other hand, there may even be more species within the human family: dating methodology
Dating and the revision of the molecular clock method – the old method
Until relatively recently, the conventional view of human evolution, culminating in the emergence of our own species Homo sapiens, was a story of survival and extinction that took place over 6 million years. This was based on what is known as the molecular clock method in conjunction with the fossil record,
DNA analysis measured in terms of mutations
As two species diverge from a common ancestor, their DNA becomes increasingly different, largely due to the accumulation of random mutations. Geneticists use DNA to assist in tracing events in a species’ past including information about their common ancestry and speciation. The amount of genetic difference between two related species is therefore proportional to the length of time since they diverged. To estimate when the divide between humans and chimpanzees occurred, for example, geneticists simply count the differences in matching stretches of chimp and human DNA and divide it by the rate at which mutations accumulate. This “molecular clock method” came up with a baseline of 4 to 6 million years ago when the human-chimp split is said to have occurred, but paleontologists considered this date as unduly conservative – in other words, they said the split had to have been older than that.
So are there more species within the human family?
The crucial factor is the rate at which these genetic mutations have been occurring, and recent research has tended to suggest that the molecular clock ticks more slowly than had previously been thought, pushing the human-chimp split further back in time[3]. This new research tends to suggest that the human lineage went its separate way at least 7 and possibly as far as 13 Mya. The result is that the fossil discoveries of Ardipithecus ramidus (‘Ardi’), a 4.4 million year old fossil from Afar, Ethiopia, Sahelanthropus tchadensis (6 to 7 Mya) and Orrorin tugensis (c 6 Mya) - all found during a burst of palaeoanthropologist discovery during the late 1990s and early 2000s and referred to below - were once thought to be outside the pale of humankind, even though they all had distinctly human characteristics. Under the new regime, they now emerge as possible human ancestors:
[1] Wood, op cit, 30-31.
[2] Article by Elizabeth Lopatto, “After 1.8m years, skulls prompt new look at humankind”, SMH, Oct 19-20, 2013, summarizing the findings of an article published in the journal Science.
[3] The process of calculation is set out in the article “Our true dawn”’ by Catherine Brahic in New Scientist, 24 November 2012, 34 at 36.
Other factors: expansion in brain size and improvement in tool making and hunting techniques
During the past million years, several new types of hominins appeared in different parts of Africa and Eurasia, and the brains of these species expanded rapidly – as large as 1300 cc, which puts them within the range of the modern human brain size. Beginning about 200,000 years ago, there also appeared a new type of stone technology leading to new and more refined tools.
The evolution of the human brain has been said to constitute one of the four great turning points in the history of life on earth. Rapid brain growth is also considered to have something to do with the evolution of more sophisticated forms of language. As with tool use, language skills probably correlated closely with brain power, giving those individuals with slightly bigger brains a significant Darwinian advantage, and toolmaking itself may have posed a formidable enough challenge to our ancestors that it spurred the development of human language.[1] In any event, hominin brains grew quickly from about 500,000 years ago, changes providing clear evidence of increased intellectual capacity, and perhaps of increased linguistic ability.
It has also been suggested that genes have something to do with it. A new gene called miR-941 appears to have played a crucial role in human brain development, and could shed light on how we learned to use tools and language, scientists say[2]. The research team believes that it emerged between six and one million years ago after humans evolved from apes. The gene is said to have emerged fully functional out of non-coding genetic material, previously described as “junk DNA” in a brief interval of evolutionary time. This is said to be the first time a new gene carried by humans and not by apes has been shown to have a special function in the human body. The gene is highly active in two areas of the brain, controlling decision-making and language abilities, with the study suggesting it could have a role in the advances functions that make us human.
Homo’s expansion in diet
There is also another aspect to this, explored by Kate Wong in an article in the Scientific American in April 2014[3]: well before the vegetation eating australopithecines became extinct around a million years ago, the species Homo expanded its diet to include increasing amounts of animal protein and fat and in the process became a hunter. Well before the time of Homo ergaster our human ancestors had developed a capability to run long distances, aided by the loss of body fur and the gain of sweat glands that enabled them to cool whilst in hot pursuit. They also developed other traits that greatly assisted in high speed hunting and throwing technique, which did not emerge in lockstep, but rather in mosaic fashion over a period. A longer waist and straighter upper arm bone appeared early on in the Australopithecines, and a shift in shoulder-socket orientation – sideways instead of upwards as in the case of the great apes – debuted some two million years ago in Homo erectus. Natural selection did not favour any particular trait for a particular purpose. Our tall waist, for example, seems to have arisen as part of a package of traits that facilitated upright walking. But later, in conjunction with other complementary features, it helped our ancestors’ increase their torque production so as to hurl an object at a target with greater force.
Stone tools and cut-marked bones reveal that early humans started butchering animals by 2.6 million years ago, but the earliest unequivocal evidence of hunting (wooden spears and animal remains at Schoningen) was just 400,000 years old. Archaeological evidence in the Olduvai Gorge in Tanzania suggests that some 1.8 million years ago, early humans were transporting carcasses of wildebeest and other animals there to carve up and eat.
In turn, Homo’s shift to a calorie rich meaty diet fuelled brain growth led to an increase in brain size facilitating the invention of technologies that permitted our ancestors to obtain even more meat and high-quality plant foods that in turn powered the further expansion of grey matter. As a result, between two million and 200,000 years ago, brain size swelled from roughly 600 cubic centimetres on average in the earliest representatives of Homo to around 1,300 cubic centimetres in Homo sapiens.
Similar themes are explored by Ian Tattersall, a paleoanthropologist at the American Museum of Natural History in New York City: the abandonment of the trees, its effect on our anatomy, the advent of stone tools dating back some 2.6 Mya, the consequent improvement in hunting technique, and the inclusion of animal proteins in diet fuelling a rapid expansion in brain size. In fact the rate of increase in size doubled between 2 and 1 Mya, and then by 200,000 years ago doubled again, this being also associated with our species ability to use symbols, another factor which made it possible for them to eliminate all hominin competition in a short space of time[4].
And, Kate Wong goes on to say, this is why humans have colonised every corner of the globe. For the first five million years of hominin evolution, our predecessors remained within the bounds of Africa, but sometime after two million years, Homo began to expand its reach into other parts of the Old World. Was hunting and its sequelae the root cause leading our ancestors to take those “first fateful steps out of Africa” and then in due course to eliminate all hominin competitors in such a small period of time?[5] Wong and Tattersall certainly appear to think so.
Stop press!
But there is a rider to all this, and Kate Wong is at the thick of things again[6]. This involves the discovery of tool remnants at a site called Lomekwi 3 near Lake Turkana in northern Kenya dating back some 3.3 million years, long before the genus Homo appeared on the scene. If substantiated, these remnants, the product of knapping – the striking of one rock one rock against another to produce a sharp-edged flake - would appear to debunk the theory that homo-kind’s techno-dependence began to form during a period of global climate change between 3 million and 2 million years ago, when Africa’s woodlands transformed into savannah grasslands; that the large-brained Homo responded to this by turning bipedal and inventing stone tools that gave it access to a wide variety of food sources including animals, and that by a feedback loop, the species’ brain size - and corresponding powers of innovation - fuelled by more calories, increased even further. The new discoveries predate the climate shift which was supposedly the genesis of all this chain of creativity.
Wong traces the history of previous discoveries along this line[7]:
And an even bigger question: why are the Lomekwi tools so isolated in point of time – predating the next oldest too discovery at Gona by nearly 700,000 years? “If stone tool manufacture was the game-changing development that experts have always thought it to be, why did it not catch on as soon as it first appeared and initiate the feedback loop that expanded the brain?”[8]
[1] Dietrich Stout, "Tales of a Stone Age Neuroscientist - How cognition evolved", Scientific American", April 2016, 20-27.
[2] “What makes us human: ‘unique’ evolution gene found”, SMH, 15 November 2012. The study is the work of a team led by Martin Taylor at the Institute of Genetics and Molecular Biology at the University of Edinburgh, and was published in the journal Nature Communications.
[3] Kate Wong, “Rise of the Human Predator”, Scientific American, April 2014, 32-27.
[4] Ian Tattersall, “If I had a hammer”, Scientific American, September 2014, 39-43.
[5] Wong, op cit, at 37; Tattersall, op cit at 41,43.
[6] Kate Wong, "The new origins of technology", Scientific American, May 2017, 22-29. What follows is an edited summary of this article.
[7] Ibid, 26.
[8] Wong's question, ibid, 28.
And, Kate Wong goes on to say, this is why humans have colonised every corner of the globe. For the first five million years of hominin evolution, our predecessors remained within the bounds of Africa, but sometime after two million years, Homo began to expand its reach into other parts of the Old World. Was hunting and its sequelae the root cause leading our ancestors to take those “first fateful steps out of Africa” and then in due course to eliminate all hominin competitors in such a small period of time?[5] Wong and Tattersall certainly appear to think so.
Stop press!
But there is a rider to all this, and Kate Wong is at the thick of things again[6]. This involves the discovery of tool remnants at a site called Lomekwi 3 near Lake Turkana in northern Kenya dating back some 3.3 million years, long before the genus Homo appeared on the scene. If substantiated, these remnants, the product of knapping – the striking of one rock one rock against another to produce a sharp-edged flake - would appear to debunk the theory that homo-kind’s techno-dependence began to form during a period of global climate change between 3 million and 2 million years ago, when Africa’s woodlands transformed into savannah grasslands; that the large-brained Homo responded to this by turning bipedal and inventing stone tools that gave it access to a wide variety of food sources including animals, and that by a feedback loop, the species’ brain size - and corresponding powers of innovation - fuelled by more calories, increased even further. The new discoveries predate the climate shift which was supposedly the genesis of all this chain of creativity.
Wong traces the history of previous discoveries along this line[7]:
- Louis Leakey’s 1964 discovery of Homo-like fossils and stone tools at Tanzania’s Olduvai Gorge dating back 1.8 million years and attributed to Homo habilis;
- Even older Olduwan stone tools located in the 1970s at a site called Gona in Ethiopia, dating back 2.6 million years ago (mya), providing the first hint that stone tools may have predated Homo. The oldest known Homo fossil at that stage was 2.4 million years old (myo);
- The discovery by archaeologist Hélène Roche of 2.3 myo Olduwan tools at a site in Northern Kenya dubbed Lokalei 2c;
- The 2010 discovery of animal bones bearing cut marks dating back 3.4 mya,at Dikika, Ethiopia, hundreds of thousands of years before the oldest known traces of Homo, , these being credited to Australopithecus afarensis.
And an even bigger question: why are the Lomekwi tools so isolated in point of time – predating the next oldest too discovery at Gona by nearly 700,000 years? “If stone tool manufacture was the game-changing development that experts have always thought it to be, why did it not catch on as soon as it first appeared and initiate the feedback loop that expanded the brain?”[8]
[1] Dietrich Stout, "Tales of a Stone Age Neuroscientist - How cognition evolved", Scientific American", April 2016, 20-27.
[2] “What makes us human: ‘unique’ evolution gene found”, SMH, 15 November 2012. The study is the work of a team led by Martin Taylor at the Institute of Genetics and Molecular Biology at the University of Edinburgh, and was published in the journal Nature Communications.
[3] Kate Wong, “Rise of the Human Predator”, Scientific American, April 2014, 32-27.
[4] Ian Tattersall, “If I had a hammer”, Scientific American, September 2014, 39-43.
[5] Wong, op cit, at 37; Tattersall, op cit at 41,43.
[6] Kate Wong, "The new origins of technology", Scientific American, May 2017, 22-29. What follows is an edited summary of this article.
[7] Ibid, 26.
[8] Wong's question, ibid, 28.