Table of Contents
- a. The Survival Value of Increased Cranial Capacity
- b. The Importance of Meat
- a. The Dilemma
- b. The Solution: Premature Birth and An Elongated Childhood
- a. The Human Genetic Bottleneck
- b. Symbolic Thinking: Art, Language and Self-Awareness
i. The First Art
- a. Humans and Denisovans
- b. Humans and Homo Erectus
- c. Homo Floresiensis
It is a deep part of human nature to want to understand our origins. Indeed, creation stories are ubiquitous among the world’s cultures. Somewhat fittingly, the vast majority of these creation stories have the human race emerging quickly, if not instantaneously—a revolutionary moment befitting a revolutionary species. When it comes to the story from science, on the other hand, while it may be no less spectacular, it is far less abrupt, for it has our species emerging much slower. Indeed, the latest findings indicate that we began branching away from the species to which we are most closely related—the chimpanzee—some 7 million years ago, and that only a series of small modifications spread out over this time has led us to our current state.
However long the process may have taken, though, in the end it was nevertheless revolutionary, for it has changed us from head to toe. Or rather, from toe to head, for the evidence indicates the process began with a modification in our big toe (which made upright walking easier) and ended with self-awareness (which ultimately made us interested in the story of our origin). While the rough edges of this story have been known for decades, recent fossil finds and new techniques in DNA analysis in the past 5 years have allowed the story to come into much clearer focus. Armed with these new discoveries, science writer Chip Walter takes on the story of human origins and evolution in his new book Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived.
The story begins with our ancestors living in the rain forests of Africa roughly 7 million years ago (much like our closest living relatives, the chimpanzees, continue to do to this day). At the time, a changing climate was beginning to threaten these rain forests, and causing them to recede. As the rain forests receded, our ancestors living at the outer edges were increasingly pushed out onto the savanna—a new and hostile environment to which they were not well adapted. Adapt or die was the reality of the day, and fortunately, our ancestors began to do so. (Actually the line between our ancestors and ourselves is not so direct: as the author points out, it is now thought that at least 26 other proto-human species arose, but that ours is the only one that remains).
First things first, it is now thought that a mutation emerged that allowed our big toe to support more of our body weight, and this made it easier for our ancestors to walk upright—which held many advantages, including efficiency in locomotion, and enhanced sight lines. From here, other mutations followed that further facilitated our ability to walk bipedally—including a complete pelvic restructuring.
At the same time as our bodies were being restructured for the purpose of walking upright, our brains were also beginning to grow. This was highly adaptive, it is thought, for it allowed our ancestors to better cooperate for the purposes of securing new sources of food, as well as fending off new predators. It was the increased sources of protein out on the savanna (and the energy that it provided) that allowed our brains to evolve larger in the first place, and once our brains began to evolve larger it allowed for increased cooperation and even more sources of protein—thus putting into effect a positive feedback loop that was leading to very large brains indeed.
Unfortunately, our two latest adaptations were coming into conflict, as bigger brains became harder and harder to birth out of narrowing hips (which were choiceworthy for upright walking). Rather than compromise, though, evolution had another trick up its sleeve: it simultaneously delayed our development, and also started forcing us out of the womb sooner, before our brains had grown so large that they would not be able to fit. The solution was ingenious but extremely dangerous, for it left us far more helpless for far longer after birth, which made us that much more susceptible to being taken down by predators. Nevertheless, the slowed development also had its advantages, for it afforded us a much wider window within which to learn about our environment, which helped us adapt to and overcome it.
In the final piece of the puzzle, the ability to think symbolically arose, and this ability not only contributed to our being able to communicate with sophisticated language, but also with our being able to represent ourselves symbolically, which ultimately allowed for self-awareness. Both of these capacities allowed for the rise and flourishing of culture, which represents our greatest advantage as a species.
The author closes with a look at where evolution (both natural and man-made) may take us in the future (or not—as our success may yet spell our demise).
To check out this book at Amazon.com, or purchase it, please click here: Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived
The following is a full executive summary of Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived by Chip Walter
Our story begins in the rain forests of Africa some 6-7 million years ago (loc. 171). At this time, our species had not yet branched away from our closest living relative, the chimpanzee. However, this was soon to change. Indeed, a period of significant global warming was just over the horizon, and this climate change would ultimately begin to threaten the habitat that we had adapted to over millions of years (loc. 175). As Walter explains, “as the planet generally warmed, some parts of the world became wetter, and more tropical, while others grew drier. Among these were northeast and north-central Africa, where grasslands were gradually transforming themselves into desert, and rain forests were breaking up into semiwooded savannas” (loc. 184).
Those ancestors of ours living deep within the rain forests may not have been affected, but those living on the fringes witnessed their old home disappear. The only viable option for them was to venture out onto the expanding savanna. Even this was not a terribly inviting option, though; for our ancestors—accustomed to plucking fruit, nuts and foliage from trees, and having to contend with few top-predators—were now thrust into a world where their traditional sources of food were gone, and where they were exposed to all manner of predators. Our ancestors’ only prospect was to evolve or die, and fortunately, at least some did do the former.
The first lucky evolutionary break that our ancestors caught, it seems, is that a fortuitous mutation led to a straightened-out big toe that was able to support much more of our body weight, thus greatly facilitating upright walking. It has been noted that the big toe of our chimp relatives starts out straight, and then curls-up in development (loc. 277). The curled toe is useful to chimps for facilitating the grasping of tree limbs (loc. 277). However, the attribute would have been useless to those ancestors of ours who had transitioned to the savanna.
A straightened-out big toe that facilitated upright walking, by contrast, would have been much more useful. As Walter explains, “in a partially wooded savanna, where the grasslands were expansive and the forest broken and less dense, an ape with a straight big toe would be lucky indeed. That deformity would enable him to stand and walk upright. Without a straight big toe our current brand of walking would be impossible. With every step we take, our big toes support 30 percent of our weight, and they make the upright running, jumping, and rapid shifts in direction we excel at possible” (loc. 291). In connection with this, upright walking has been shown to be a far more efficient way to travel over flat ground than knuckle-walking (which is what our ape relatives do), and also confers an advantage in that it allows the erect individual to see far further over the horizon (thus making it easier to spot potential predators as well as prey) (loc. 268-71).
Once the value of bipedal locomotion had been proven, the way was cleared for a more radical restructuring of our bodies to facilitate upright walking even more. This radical restructuring included a modified neck, as well as a full reworking of our pelvic area (loc. 297). This latter modification would eventually prove to have very important consequences indeed (as we shall soon see).
a. The Survival Value of Increased Cranial Capacity
As our bodies were evolving to adapt to our new environment, so were our brains; and here it was size that mattered. Fortunately, our ancestors had a head start. Indeed, apes already had the biggest brains in the animal kingdom (a legacy that has been passed down to this day). Interestingly, one of the main reasons why apes (and even monkeys) are thought to have evolved bigger brains in the first place is because this helped them negotiate more and increasingly complex social relationships. In support of this theory, it has been noted that there is “a correlation between the size of an ape’s brain and the size of the troop in which he lived” (loc. 1126). The psychologist who discovered this little curiosity, Robert Dunbar, explains the rationale thus: “bigger troops drove the evolution of larger brains because every new addition to the group ratcheted up the number of direct and indirect relationships each member had to keep track of. Juggling more relationships required a corresponding boost in intelligence. Evolution would have favored smarter, larger-brained members of the troop because they would have been better equipped to track the growing social relationships between fellow primates” (loc. 1130).
So our savanna-bound ancestors had already begun to evolve larger brains and increased sociality, and this certainly would have helped them adapt to their new environment. For one thing, big brains are good for learning new and innovative ways to survive (which would have been invaluable in an unfamiliar environment). But also, and perhaps more importantly, big brains allow for individuals to work together to reach their goals; in other words, big brains allow for cooperation.
Even our chimpanzee relatives show some rudimentary ability to cooperate (loc. 407), and so we have reason to believe that our ancestors new to the savanna would have employed cooperation as well. However, the survival value of cooperation would have been that much more acute out on the open plain. As Walter explains, “on the savanna there were more predators, but fewer places to hide, less food, less water, than the jungle provided, even more competition from other troops given the dearth of resources in their new home… You find yourself awakening every day bound to your fellow creatures working to survive, raising children, forging relationships and alliances, scrounging for food, and communicating as much as your brain and body will allow. You have no other choice because if you don’t you will die” (loc. 1105).
Given the increased value of cooperation out on the open plain, and given that bigger brains allow for increased cooperation, the selection pressure was there for our brains to evolve even larger. Throw in the fact that bigger brains are also good for finding increasingly sophisticated tricks for surviving in a foreign environment (including using and making tools, which was to come later), and you have yourself a perfect prescription for expanding cerebral capacity; and the evidence is that this is exactly what occurred. As Walter explains, “while a chimp’s brain is about 350 cc, these grassland primates’ brains ran from 450 cc to 500 cc, a 25 to 40 percent increase” (loc. 304).
b. The Importance of Meat
Still, the brain is no small consumer of energy, and the bigger the brain, the more calories it burns through. So just where were we getting the added energy that we would have needed to feed our bigger brains? Simple: meat. Though our new flatland environment was bereft of an abundance of fruit, nuts and foliage, it did contain an important source of food that the jungle lacked, and that was carrion (loc. 410). And, as Walter points out, carrion is especially loaded with calories (loc. 419). As the author explains, “fruit and foliage became increasingly rare, and these humans had to cover more distance to gather it, which required still more energy. Ultimately that was not a sustainable survival strategy. But if you could get your hands on some meat! Then you were instantly rewarded with much more nutritional bang for your hunting-and-gathering buck. That is precisely what the robust lines of savanna humans did” (loc. 419).
Nor, it seems, was this dietary shift of our ancestors all that much of a leap. Indeed, today’s chimpanzees are known to eat insects and even small animals out in the rain forest; and therefore, there is reason to believe that our ancestors would already have had the capacity to stomach protein as they headed out onto the savanna. Nevertheless, our jaws, teeth and guts did eventually do some evolving to permit an ever increasing percentage of our diet to come from meat (loc. 407-10, 424).
The more we came to rely on meat in our diet, the more energy we were able to attain, the more our brains were able to grow, the better we were able to cooperate (and the more sophisticated tools we were able to create) to secure even more meat (loc. 432). This positive feedback loop eventually yielded us very large brains indeed (more on this below).
The importance of meat in the survival and evolution of our species cannot be overstated, for it appears as though other early upright hominids (known as australopithecines) were directed away from this path, and instead continued to rely on foliage in their diet (loc. 427). The brains of these hominids did not grow as ours did, and eventually they went extinct (some 1.2 million years ago) (loc. 427).
So meat saved the day and allowed for a growing brain (thank you, meat); but this isn’t the end of the story. For we have good reason to believe that our brains were not only growing, but also changing in design and orientation. The evidence tells us that our species not only has the brain power to cooperate, but that at least a part of us is naturally inclined to do so. In other words, moral sentiments (which facilitate cooperation) are innately built in. This is evident from the fact that while the cultures of the world are known to have somewhat differing conceptions of right and wrong, there are nevertheless some deep similarities across cultures when it comes to questions of fairness and morality (loc. 1017-32). What’s more, these deep similarities are evident from a very early age (loc. 1010-17), as the following video exhibits.
Given that cooperation would have been especially adaptive in our new and hostile environment, it stands to reason that our natural moral sentiments would have begun evolving around this time. Of course, none of this is to say that our new moral sentiments came to completely override our more self-serving instincts. The fact is that while cooperation may have been adaptive, it would never serve an individual to sacrifice themselves entirely for the group. What we were left with was a kind of divided psyche: the individual torn in opposite directions. As Walter explains, “living in such a tight community also means competing with the selfsame creatures you rely upon for mates and status and resources. Tricky situation, because it requires balancing what you want for yourself with everyone else’s needs. It means simultaneously taking care of number one and watching out for the good of those around you. This is the central paradox of the human condition—balancing, constantly, two seemingly opposite needs. We see the evidence of this continuing dilemma every day from sibling rivalries to office politics, from international trade to military balances of power” (loc. 1109).
PART II: EVOLUTIONARY GROWING PAINS, AND BREAKTHROUGHS: PREMATURE BIRTH AND THE BIRTH OF CHILDHOOD, ADVANCED LEARNING, AND CULTURE (AND THE FIRST FORAY OUT OF AFRICA)
a. The Dilemma
Now, this added moral dimension of ours was not the only way that our brains were redesigned and reoriented following our split from our ancient ape ancestors. Indeed, the remainder of our evolutionary story largely has to do with additional facets of this cerebral redesign. However, before delving further into this topic, we must first return to the issue of our increasing brain size; for this holds the key to the next step in our story.
It was mentioned above that our move towards bipedal walking included a complete pelvic restructuring. Part of this restructuring involved narrower hips, for narrowing hips facilitated our bipedal gait (loc. 452). This was all well and good, but for the fact that our growing brains did not agree at all with this little arrangement. For the bigger the brain, the more room it needs to exit the womb (loc. 456). The two adaptations were coming into direct conflict with one another. One would have to give. Or would it?
b. The Solution: Premature Birth and An Elongated Childhood
As it happens, nature found another way out of the dilemma. The solution included 2 aspects. First, the birth process itself was pushed forward. In other words, we started being born prematurely, before our brains had grown so large that they would not be able to fit through the womb. And the change here was dramatic, as, all-told, our pregnancies are roughly a year shorter than the pregnancies of other apes. As Walter explains, “if you, for example, were to be born as physically mature and as ready to take on the world as a gorilla newborn, you would have to spend not nine months in the womb, but twenty, and that would clearly be unacceptable to your mother. Or, looked at from a gorilla’s point of view, we humans are born eleven months ‘premature.’ We do not reach full term, which makes us fetal apes” (loc. 462). That we are indeed ‘fetal apes’ for the first year of our life is reflected in the fact that we are almost completely helpless during this first year (loc. 654).
Now, not only are we born prematurely, but it also takes us far longer to develop outside of the womb than it does for other apes (and this is the second part of the solution to our dilemma). As Walter explains, “You and I, we already know, take eighteen to twenty years to reach physical adulthood, whereas chimpanzees and gorillas reach adulthood by age eleven or twelve, in nearly half the time” (loc. 2220).
And this discrepancy in development is even more accentuated when it comes to our heads and what’s inside them. Indeed, while your average chimp brain is finished developing within a year after birth, our own continues developing for neigh on two full decades. As the author explains, “a chimpanzee completes all of its brain growth within twelve months of birth. You and I, however, came into the world with a brain that weighed a mere 23 percent of what it would become in adulthood. Over the first three years of your life it tripled in size, continued to grow for three more years until age six, underwent massive rewiring again in adolescence, and finally completed most, but not all, of its development by the time you reached your second decade” (loc. 547).
Stretching out our physical development, and allowing more of it to occur outside of the womb, allowed our heads (and brains) to grow even larger, and ensured that they would not grow so large so fast that we would not be able to fit through the womb. Thus both our premature birth and our elongated development contributed to allowing us to keep our big brains without sacrificing our slender hips. These modifications of ours are thought to have begun some 2 million years ago (loc. 564), and they quickly led to a massive increase in our brain size (as can be seen in the chart below).
In addition to allowing our brains to grow larger, it appears that our elongated development also had another benefit: and that was that it increased the window during which our brains remained especially plastic. This increased the degree to which we were able to learn from our environment for the purposes of adjusting to it (loc. 540). In other words, our elongated development allowed us to shift our behavior from mindless instinct towards more mindful learning. As Walter explains, “it’s… our long childhoods, that makes our epigenome so inclined to the influences of our personal experience during the first seven years of life. Because we are born early and since we have extended our brain development well beyond the womb, neuronal networks that in other animals would never have been susceptible to change remain open and flexible, like the branches of a sapling. Although other primates enjoy these ‘sensitive periods,’ too, they pass rapidly, and their circuits become ‘hardwired’ by age one, leaving them far less touched by the experiences of their youth. This epigenetic difference helps explain how chimpanzees, remarkable as they are, can have 99 percent of our DNA, but nothing like the same level of intellect, creativity, or complexity” (loc. 906).
This enhanced intellect, creativity and complexity of ours would eventually allow us to fashion the first truly sophisticated stone tools (as well as many other cultural innovations)—and also to pass down these innovations to future generations for further enhancement. In other words, our increased brain size eventually allowed for culture itself. Here is how Walter breaks down this process: “there is no way to overestimate how important this was to our evolution. This was the birth of human childhood itself, and the beginning of wild and complicated processes that explain how you or I can be born in Fargo, North Dakota, learn to speak fluent French in Paris, develop wit like Woody Allen’s, or become as reclusive as Howard Hughes, all while still plumbing the intricacies of subjects as wildly different as calculus, Mozart, and baseball. This began the trend that has, in many ways, made children of all of us the entire course of our lives, neurologically nimble enough that we can keep learning, changing, and overriding the primal commands of our DNA” (loc. 979).
It didn’t take long for our increasing brain size and our increasing ability to learn to demonstrate its worth. Indeed, by 1.9 million years ago many early hominins were already beginning to leave Africa, and spread to other parts of the world.
By the time the first hominins left Africa around 1.9 million years ago (loc. 1497), they had already fashioned the first stone tools (Oldowan stone choppers—a technology that would soon be replaced by the much more advanced Acheulean hand axes [loc. 1508], both pictured below), and they would soon master fire (loc. 1509). This first wave out of Africa, made by a species known as Homo erectus, spread out through much of the old world, including the Middle East, Asia and Indonesia. As Walter explains, “before long, wave after wave of Homo erectus were settling parts of Arabia, China, even Indonesia, though they apparently never made it as far as Australia” (loc. 1508). By 1.3 million years ago, erectus, or, rather, one of its descendants (Homo antecessor [loc. 1528]), had reached Europe (loc. 1524).
Oldowan choppers (2.6-1.7 million years ago):
Acheulean hand axes (1.7-0.3 million years ago):
Homo erectus migration:
The fact that Homo erectus had managed to migrate so far—and adapt to such a wide range of environments—is a testament to the degree of adaptability that had been achieved by these hominins. As Walter explains, “something more than simply human wandering was afoot here. The lands where these creatures were settling not only stretched from Indonesia to North Africa, but represented a widening variety of environments. They ran the gamut from marshes and streams to seacoasts and wooded mountainsides. The creatures were not only putting more distance between themselves and their home continent, but between themselves and the dictates of their genes. They were using their brains and creativity to adapt. While the other great apes had for millions of years been retreating to increasingly smaller forests, sticking to familiar environments where they were comfortable and for which they were genetically suited, these ancient humans, armed with their tools, clothing, and that magical thing called fire, were adapting their new environments to them, not the other way around” (loc. 1524).
As impressive as all of this migration and adaptation was, though, Homo erectus was not the species that would eventually evolve into Homo sapiens. Rather, our stock would come from a species that continued to live exclusively in Africa at this time (and that would later evolve into a species known as Homo heidelbergensis [loc. 1528]). Indeed, it is thought that our species would not make its way out of Africa until about 50,000 years ago (loc. 1463, 1590, 2020) (though there is evidence that some upstarts left as early as 100,000 years ago [loc. 1660]).
Before our ancestors embarked out of Africa, though, another species would branch off from this group of ancestors of ours, and head off to Europe: Neanderthals. Indeed, as Walter explains, “the creatures, the people, who later evolved into Homo sapiens and Neanderthals began to part ways, genetically speaking, from heidelbergensis almost as soon as heidelbergensis itself emerged. Some members of the species remained on Africa’s horn… but others, with a more extreme case of wanderlust, moved northwest across a new green Sahara to Gibraltar and then into Europe, following in the footsteps of Homo antecessor” (loc. 1542). As you may have guessed, the members of heidelbergensis that remained in Africa would later evolve into us, while the wanderlusting, Europe-bound members of this species would later evolve into Neanderthals (loc. 1574). The Neanderthals would eventually spread all over Europe, “as far west as the Iberian Peninsula and as far east as the Altai Mountains in southern Siberia” (loc. 1853).
The two branches of heidelbergensis (us and Neanderthals) are thought to have split some 200,000 to 250,000 years ago (loc. 1375). That makes Neanderthals by far our closest evolutionary ancestors (surviving or not). This in itself makes Neanderthals very interesting. However, there is another reason why Neanderthals are of particular interest. And this is because we would eventually live side by side with them in Europe for thousands of years before they finally went extinct. This being the case, it is expected that piecing together the story of just how this co-existence played out, and how and why Neanderthals went extinct, will tell us much not only about Neanderthals, but ourselves.
However, before turning our attention to this human/Neanderthal co-existence (and eventual extinction of the latter), let us first take a look at Neanderthals on their own—beginning with their forebears, Homo heidelbergensis.
When it comes to heidelbergensis’ physiology, the evidence indicates that it differed in a few important respects from that of Homo erectus. As Walter explains, “the original heidelbergensis was, it seems, thick boned, huskier and stronger than erectus, who was taller and slimmer. Not that at six feet he was short, but with a frame that easily supported two hundred or more pounds, he was built like a bouncer, or college fullback” (loc. 1551).
The members of heidelbergensis who eventually moved into Europe kept this husky physiology, and even added to it as they evolved into Neanderthals (loc. 1557). As Walter explains, “the colder climate favored thicker, stockier creatures that exposed less of their bodies to the air… The strength and endurance these bodies were apparently blessed with were certainly assets as they dealt with a punishing climate” (loc. 1557). (Those heidelbergenses who remained in Africa, on the other hand [our direct ancestors], would eventually begin doffing this robust build, in favor of a more gracile form [this is more significant than we might think, as we shall soon see]).
In any event, returning to Homo heidelbergensis for a moment, it is difficult to tell just how much this species had evolved intellectually before splitting off into its separate branches (though there is much speculation about this [loc. 2601]). Nevertheless, much more is known about the intellectual life of Neanderthals.
To begin with, the evidence indicates that Neanderthal brains eventually grew to a size of 1100 cc to 1400 cc (which is as large as ours), and even as big as 1700 cc. (loc. 1545, 1850, 1857). This big brain allowed Neanderthals to make several impressive innovations. For example, as Walter explains, “the archaeological evidence suggests that these nomads became the first humans to build shelters, probably of rock and wood, and hunted big game, like Irish elk, mammoths, and European lions, with long wooden spears” (loc. 1545). These hunts apparently reached stunning sophistication. As Walter explains, “one site that dates back 125,000 years reveals that a group of Neanderthals living in a cave at La Cotte de Saint Brelade drove mammoths and rhinoceroses over a nearby cliff, butchered the dead or writhing animals on the spot, and then hauled in the choicest cuts into their nearby caves before any hungry predators could get to them” (loc. 1882). As the author points out, “efforts like that took brains and cooperation and sophisticated communication. Their culture was advanced and their social structure tight and fair, otherwise they would never have survived as long as they did” (loc. 1882).
Over and above this, there is also evidence that Neanderthals had a softer and more contemplative side, as they both cared for their sick, and buried their dead in a ritualistic way (loc. 1882-92). As Walter explains, “behaviors like these tell us that Neanderthals probably felt the loss of death, mourned those close to them who had met their end, and, by extension, understood there was something more to life than the day-to-day problems it presented. They, like our ancestors, must have wondered what follows death” (loc. 1895).
It was mentioned above that the sophistication of Neanderthal hunts suggests that they had developed fairly complex communication. However, there is some debate over just how complex this communication was. On the one hand, there is evidence that Neanderthals had lateralized brains (which is an indicator of language capabilities [loc. 1551]), as well as a refined sense of hearing, and also the FOXP2 gene (both of which are connected to speech in our species [loc. 1548]). On the other hand, there is evidence that the range of sounds that Neanderthals could both utter and hear were far more limited than in our species (loc. 1955-71), which would suggest that their language was not as sophisticated as our own (loc. 1971).
While Neanderthal brains were just as big as ours (and even a little bigger), and while the jury may still be out on just how complex their language was, it does seem clear that they simply did not develop the same mental sophistication that we did. One of the main reasons for thinking this is that by the time humans and Neanderthals met in Europe some 50,000 years ago, human tools were far more advanced than those of Neanderthals; and, in fact, Neanderthal tools improved very little (if any) in their entire 200,000 year history (loc. 1995). As Walter explains, “the Mousterian tools and cultural artifacts they crafted and left behind show remarkably little innovation considering how long they were around” (loc. 1998). To take just one example, though the Neanderthals did make spears, they were fit only for thrusting at a target from close range, and they never did manage to innovate spears that were capable of being thrown or launched with a sling (as we did) (loc. 1559, 1779, 1899, 2027).
As it turns out, there may be a very good reason why Neanderthals never developed the mental sophistication of early humans. To begin with, it was mentioned above how our increasingly elongated development was allowing for more learning and mental flexibility. While this process continued to ratchet up in our ancestors in Africa, it seems to have slowed down and even reversed in Neanderthals. As Walter explains, “a Harvard researcher named Tanya Smith and her colleagues, after the careful inspection of many teeth, concluded that not only did Neanderthals not lengthen their lives or their childhoods… they had actually shortened them… Smith says Neanderthals reached full maturity by age fifteen, three to five years earlier than us and not terribly different from the pace that Nariokotome Boy was on, nearly a million and a half years earlier” (loc. 2239).
But if the benefits of an elongated development were clear, why would the process have been halted, and even reversed, in Neanderthals? Simple: environmental stress. As Walter explains, “Neanderthals… had a rough time of it fighting cold climates and hunting enormous animals at close quarters, among other challenges. Their population… never took off, which meant from the first moment they emerged, they were, essentially, an endangered species… Because they were so quickly snuffed out, and because they congregated in small groups, evolution apparently began to favor Neanderthal children who grew up faster, could bear children sooner, and reached adult size and strength as rapidly as possible to replace the older members of the troop who passed on so quickly” (loc. 2249).
A shortened youth may have helped Neanderthals survive the harsh conditions they faced; however, a further effect was that their brains were not given the same window of plasticity and flexibility as ours were, and this led to less opportunity for adaptation via learning (loc. 2249, 2709). Ultimately, the difference may go a long way in explaining why Neanderthals did not reach the same cognitive sophistication as we did, and also why we survived whereas Neanderthals did not (loc. 2252, 2706) (more on this below).
This, then, brings us back to us humans. While Neanderthals were busy evolving up in Europe, our direct ancestors were busy doing so back in Africa. As mentioned above, the process of elongating our development continued, leading to more adaptation via learning. However, environmental conditions in Africa were soon about to test this adaptability of ours to the extreme.
About 70,000 years ago, the earth had descended into the grips of a devastating ice age (loc. 1387, 1394). But that’s not all; as Walter explains, “this climatic shift sabotaged life everywhere, as we will see, and may have been further boosted by the largest known volcanic eruption in the history of earth on Sumatra, Indonesia, which blasted ash into the stratosphere, causing a ‘volcanic winter’ that rapidly accelerated the cooling of earth” (loc. 1389).
The combined effect of the ice age and the volcanic eruption were particularly hard on the species of Africa (including our own), as much of the ash from the volcano drifted over from Indonesia and settled on the African continent (loc. 1438-44). At this time, it is thought, our species dwindled down to very few—as few as 10,000—members. We were on the verge of extinction, and hanging on by a mere thread.
Fortunately, the forces that were threatening our species eventually began to dissipate and relent. As Walter explains, “finally, fifty thousand years ago, this particular climatic pendulum began to swing in the opposite direction, and just as the ice had once relentlessly crept from the polar caps to endanger the species at lower latitudes, it now casually reversed itself, and Africa grew warmer and wetter. The sparse pockets of the human family… again found themselves blossoming and fanning out” (loc. 1419).
b. Symbolic Thinking: Art, Language and Self-Awareness
Actually, the extreme environmental pressure we faced may have been a blessing in disguise, for it appears as though it triggered some evolutionary changes in us that helped us survive, and that also turned us into the creatures we are today. To begin with, most paleoanthropologists agree that our species emerged roughly 200,000 years ago—in that, as Walter explains, ancestors of ours that lived after this time may be considered “anatomically modern—they look like us” (loc. 2541).
i. The First Art
However, there is evidence that something in us changed dramatically around 70,000 years ago (right around the time that the world was in the depths of the ice-age mentioned above). Specifically, it is at this time that we get the first evidence of human art. As Walter explains, “around seventy-two thousand years ago… we begin to see evidence of a change in what might have been a hotbed of rapid human, intellectual development—those coastal cave communities of South Africa where… small Homo sapiens communities found themselves within a gnat’s eyelash of total annihilation. At Blombos Cave the evidence tells us that a small handful of Homo sapiens were decorating tiny nodules of hematite, a kind of iron rock, with geometric designs, cross-hatchings that may have represented some kind of symbol, still indecipherable to us. In the same cave, but later in time scientists have also unearthed perforated ornamental shell beads, arguably the first evidence of human-made jewelry” (loc. 2557). And that’s not all, “in 2010 a team of paleoanthropologists reported finding nearly three hundred fragments of decorated ostrich eggs in the Diepkloof Rock Shelter, another South African cave complex. Each shell is sixty thousand years old” (loc. 2560).
Here are some examples of the earliest art pieces from Blombos Cave:
No evidence of human art has been found prior to this point in time; and therefore, the conclusion to draw is that this is when art first arose. Now, however you may feel about art, the fact is that the endeavor requires a peculiar and very advanced set of mental attributes. As Walter explains, “it’s true tools and other technologies had been around millions of years, and they require creativity, but they are not examples of self-expression or symbolic thinking the way a piece of sculpture, or a painting… or a song are” (loc. 2538).
It is the ability to think symbolically that it is of particular importance here. Our ability to think in terms of symbols is unique in the animal kingdom, and it is arguably the single most important mental attribute that we have. For not only does it make art possible, it also allows for our enormously complex language. As Walter explains, “that is what symbols do, they translate thoughts and ideas into tight, little packages of meaning for delivery from one mind to another” (loc. 2719).
And once you are able to transmit complex ideas from one mind to another in an easy and efficient way, you open the door for an enormous explosion of culture: “with language we can express an infinite variety of thoughts, feelings, ideas, and insights… imagine how modern language must have supercharged creativity and the culture that was assembled out of it?” (loc. 2279).
But that’s not the end of it. Walter argues that the arrival of full symbolic thinking allowed for yet one more major mental capacity which also improved creativity and culture: self-awareness.
As you may have noticed, when you think to yourself, it comes off as though you are having a conversation with yourself (loc. 2750-57). There is one person doing the talking (you 1), and one person doing the listening (you 2). As Walter has it, what you are actually doing here is creating a symbol of yourself, setting it aside, and then speaking to the ‘mirror’ you. As the author explains, “when you are thinking, and talking, to yourself, the you that you are speaking to is a symbol. Like a reflection in a mirror, it is a representation made possible because your brain can generate symbols” (loc. 2882).
The ability to make a symbol of ourselves may not seem like such an incredible thing, but, as Walter points out, it does have deep practical implications: “when we could fully symbolize ourselves, it meant that we could also begin to embed our symbolic selves among all the other symbols around us. We could begin, entirely inside our minds, to imagine what we would do before we did it. We could guide our behaviors, or at least conceive of guiding our behaviors, the way a chess player moves the pieces on a chessboard. By creating a symbol of ourselves, we became conscious and self-aware, capable of purposefully planning our behavior. We could imagine. That, in itself, represents a remarkable leap” (loc. 2918).
Whatever the precise nature of the changes that were occurring in our heads at this time, it seems clear that they were serving our species well; for by 50,000 years ago our population in Africa was exploding, and our ancestors were also beginning to leave Africa and spread to every corner of the world.
In fact, our migration was so quick and so successful that by 10,000 years ago humans could be found virtually everywhere on the planet (loc. 1461). As Walter explains, “inside of ten thousand years, wandering Homo sapiens doggedly walked from the eastern Sahara to the plateaus and mountains of Western Australia. Meanwhile, other branches of our kind that had radiated into Mesopotamia and moved west spent the next fifteen thousand years settling much of Europe, as far away as Spain and well north of the Alps. Still others expanded north and east into Asia, across the highlands of Tibet and the steppes of Russia until they had nearly reached the top of the world to cross the land bridge between Russia and Alaska. From there they made for Canada, into north America and then southeast to the Meadowcroft settlement just outside Pittsburgh, Pennsylvania, sixteen thousand years ago, and finally into Central and South America to become, someday, the Incans, Mayans, Aztecs, Hopis, and scores of others. The settlers of Meadowcroft predated European explorers by a mere 155 centuries” (loc. 1477).
While our species was experiencing enormous success, the same cannot be said for other hominin species. Everywhere we went, it seems, the hominins that had come before had recently been wiped out. And those that remained would not last long. In at least a few of these cases there is evidence that humans encountered these hominins. Thus the question naturally arises: did we play a hand in their extinction? The encounters themselves are of particular interest; and therefore, we will take a look at each one by one.
Let us begin with our most well-known hominin ancestor, the Neanderthal. As mentioned above, Homo sapiens had moved into Europe by about 50,000 years ago. We know this not only from fossil finds, but also from the artifacts that these early humans left behind. As Walter explains, “their weaponry was advanced and included the invention of bone spear throwers that held their spears as they launched them at prey (and likely one another on occasion) with a force and accuracy that made them the most lethal hunters on earth. They also excelled in fashioning extremely sharp flint knife blades and spearheads. They even developed techniques for straightening their spears to make their flight more true. They liked to decorate their weapons too” (loc. 2030).
In addition to decorated weapons, these early humans also left behind their famous cave paintings. Interestingly, the earliest cave art in Europe—which is in the range of 35,000 years old—is far more advanced than the art found in South Africa from 20,000 years earlier. Gone are the simple etchings of our earlier ancestors. Here we find art of the most advanced kind. As Walter explains, “the artwork is nothing short of jaw-dropping, as beautiful and haunting as anything a modern artist could possibly conjure, and an indication that in these people, modern human behavior had irrevocably touched the world” (loc. 2034).
Here is a video of some of these cave paintings:
Given that Neanderthals were still roaming Europe when humans first arrived (and for thousands of years thereafter), it is certain that the two species must have encountered one another; and indeed, the evidence indicates that they did. As to the nature of these encounters, it appears as though it did involve at least some hostility. Specifically, a handful of cave finds suggest that the two species were killing (and eating!) one another (loc. 2072-77). Still, though, evidence of mass warfare has yet to be found (loc. 2081).
On the other hand, there is evidence that at least some of the encounters between humans and Neanderthals was of the more amorous variety. To begin with, scientists have found fossils of specimens that exhibit a mix of human and Neanderthal characteristics (loc. 2138, 2147). These fossils are suggestive enough, but the more telling evidence comes from the DNA. Scientists have been able to collect Neanderthal DNA from the fossils that they have found, and when they analyzed this DNA and compared it with that of a variety of modern humans (using “the genomes of five people from different lineages from around the world—French, Han Chinese, Papuans from New Guinea, and the Yoruba and San people of Africa” [loc. 2157]), they found something altogether shocking. As Walter explains, “what dumbfounded the project’s investigators, and the rest of the scientific world, was that all the genetic samples taken, except for the Yoruba and San people of Africa, contained 1 to 4 percent Neanderthal DNA. In other words, most of the human race from Europe to the islands of Southeast Asia (and probably farther) is part Neanderthal!” (loc. 2160).
So, humans apparently bred with some Neanderthals, and killed others off, but the evidence suggests that the majority of Neanderthals were neither killed directly by us, nor bred out of existence by our horny ancestors. Rather, it is likely that Neanderthals ultimately met their end because they were simply outcompeted by our species. After all, it is clear that our species had far more sophisticated tools and technology than the Neanderthals by the time they met. What’s more, the Neanderthal population never grew very large to begin with (loc. 2094). Outdone both in terms of mental and cultural sophistication, as well as numbers, the Neanderthals would have stood little chance of standing their ground against our invasion. As Walter explains, “the thinking is that we didn’t kill them hand to hand, but we exterminated them in a war of attrition, by taking over the best habitats and hunting grounds, killing game faster than they could, and in larger numbers. Slowly, over thousands of years, the already sparse Neanderthal population retreated to pockets where it became increasingly difficult for them to survive… This might have crippled Neanderthals’ ability to band together, weakening them still more, until in the end each of the dwindling clans died away” (loc. 2087).
Whatever the exact story may be, the Neanderthals appear to have been closing in on extinction by about 30,000 years ago, and were entirely extinguished by about 24,000 years ago (loc. 2190, 2200).
a. Humans and Denisovans
Interestingly, it appears that Neanderthals were not the only species of hominin that humans encountered in this neck of the woods. Just recently, in 2010, scientists found a tooth and a finger bone fragment in a cave in the Altai Mountains of Siberia (loc. 1640). When the scientists analyzed the DNA of the remnants, they found that it belonged to a new and as yet undiscovered ancestor of ours. This new species has now been dubbed the Denisovans (loc. 1640). Judging from the DNA, the Denisovans shared a common ancestor with both ourselves and Neanderthals some one million years ago (loc. 1648).
When scientists compared the DNA with modern humans they found another shocker. As Walter explains, scientists “were electrified when they found that between 4 and 6 percent of the genomes of the people of Papua New Guinea and Bougainville Island contain Denisovan DNA” (loc. 1651). Apparently, humans mated not only with Neanderthals, but with Denisovans as well, and the hybrid descendants that they spawned eventually made their way down to Southeast Asia (loc. 1653). Horny humans indeed!
b. Humans and Homo Erectus
Speaking of Asia, it was mentioned earlier that the hominin species known as Homo erectus had migrated there some 1.9 million years ago. Well, it seems that when modern humans moved into Asia in this latest wave, they met them too. The evidence this time around comes not from bones or teeth, but from a somewhat less heralded source: head lice.
You see, we humans are known to host two varieties of head lice, which indicates that we must have picked up each at a different time in our history (loc. 1693). We also know that “despite nearly always being in one another’s company… each initially evolved separately while dining on two different species of early humans. One of those species led to us. The other is extinct. For those two species of lice to coexist today, both had to have come into close contact sometime in the past” (loc. 1694).
Now, by studying the DNA of our head lice, scientists have concluded that we appear to have picked up one of them in Asia about 25,000 to 30,000 years ago (loc. 1697). Thus we must have encountered a group of our ancient ancestors at this time and place. Given that Asia was Homo erectus’ territory, and given that they are known to have been there near-upon this time frame, we must conclude that we did in fact meet Homo erectus on our journey, and that it was them who gave us our second species of head lice (loc. 1697-1704).
Now, the spreading of head lice requires very close contact indeed; and therefore, it seems as though our encounter with erectus must have been of the face-to-face variety. Just how friendly, or unfriendly this contact was, though, we simply cannot say, as there is no evidence either way. Whatever the case may be, it seems that Homo erectus was on the verge of extinction regardless (loc. 1696).
c. Homo Floresiensis
There is one last species of proto-human that is of interest in this part of our story, and this is a species known as Homo floresiensis. Floresiensis fossils are confined to the island of Flores, some 400 miles east of Java in Indonesia (loc. 1720). The evidence indicates that floresiensis lived there “between ninety-five thousand and seventeen thousand years ago” (loc. 1726). The species itself was fairly advanced, as the remains tell us that “these creatures could control fire, make sophisticated tools, and hunt game” (loc. 1726). None of this is all that surprising; however, what is surprising is the physical size of these creatures. As Walter explains, “the press and even astounded scientists took to calling them ‘hobbits.’ One three-foot-three-inch-tall adult-woman skeleton that was discovered turned out to be even shorter than Lucy” (loc. 1723).
Together with their tiny frames, floresiensis also had very small heads and brains: “their brain size at 420 cc was also not much larger than Lucy’s, a hominin that had walked the earth more than 3 million years earlier” (loc. 1723). But this brings up a question: just how could a creature with such a small brain have come to be so culturally sophisticated? Here is Walter to explain: “our best evidence indicates that the Flores hobbits… [were] the descendants of earlier Homo erectus settlers who were eventually reduced in size by an odd evolutionary phenomenon scientists call island dwarfing. Island dwarfing happens when natural forces cause species to shrink in size over time in isolated locations, presumably because resources are severely limited. The theory is that in a kind of ecological bargain, animals grow smaller rather than starve” (loc. 1730). Since floresienis brains had already grown quite sophisticated and complex by the time they started shrinking in size, much of their brain power was preserved despite being reduced in bulk (loc. 1742).
As to whether our ancestors encountered this species on their way to colonizing Australia, it is difficult to say. There is simply no evidence either way. Interestingly, while our best evidence indicates that the Flores hobbits had gone extinct by 17,000 years ago, not everyone is convinced. As Walter explains, “Anthropologist Gregory Forth has hypothesized that Flores hobbits might be the source of stories among local tribes about the Ebu Gogo, small, hairy cave dwellers who supposedly spoke a strange language and were reportedly seen by Portuguese explorers who came to the islands in the early 1600s. Henry Gee, a senior editor at Nature magazine, has even opined that species like Homo floresiensis might still exist in the unexplored tropical forests of Indonesia” (loc. 1749).
So are we the last ape standing? Probably, but maybe not…
By the time our species had spread to every corner of the planet, some 10,000 years ago, our newfound technological and cultural capacities were about to inaugurate another revolution: the agricultural revolution. This marked the time that we moved away from our traditional, hunter-gatherer lifestyle, and adopted agriculture instead. From here our cultural evolution exploded, and we would soon find ourselves inventing civilization.
Now, 5,000 years into our experiment with civilization, we have discovered the underlying stuff that is responsible for our biological evolution: DNA. We have even figured out how to manipulate and modify this DNA. In other words, in our species, biological evolution gave way to cultural evolution, and through cultural evolution we have now figured out how to direct our biological evolution. Just how we choose to direct our biological evolution will be the next major evolutionary phase for our species. Walter speculates that our new found power to manipulate our environment and ourselves may yet spell our demise. Considering how far we have come, and how much we have adapted to our environment, and how much we have adapted our environment to ourselves, I find this hard to believe.
The following is the best documentary that I have yet come across on the topic of our evolution from chimp to human:
To purchase this book at Amazon.com, please click here: Last Ape Standing: The Seven-Million-Year Story of How and Why We Survived
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