Propelling Human Evolution
There is a universal human nature. This universality exists primarily at the level of evolved psychological mechanisms, not of expressed cultural behaviors. ~ American psychologist Leda Cosmides, American anthropologist John Tooby, & Canadian anthropologist Jerome Barkow
Volatile climate greatly affected human descent, notably African aridity and the consequent foraging demands it put upon the genus.
Homo evolved against a background of long periods of habitat unpredictability that were superimposed on the underlying aridity trend. Key factors to the success and expansion of the genus rested on dietary flexibility in unpredictable environments, which, along with cooperative breeding and flexibility in development, allowed range expansion and reduced mortality risks. ~ Susan Antón, Richard Potts, & Leslie Aiello
Major shifts in African climate coincide with 2 moments on the hominin ancestral path, roughly a million years apart, that mark significant changes in our family tree. The 1st evolutionary shake-up happened between 2.9 million and 2.4 million years ago. The 2nd shake-up occurred between 1.9 million and 1.6 million years ago. ~ American geographic environmentalist Peter deMenocal
As with other organisms, viruses propelled hominin evolution. ~30% of adaptive amino acid changes in human proteins came as viral contributions. The human inclination towards addiction via enhanced pleasure stimulation was a viral implant.
There were also other powerful forces at work, including adaptations driven by the mind: sociality and technology. Stone implements chronicle hominins as inveterate tinkerers. This exercise doubtlessly both reflected and impacted mental and social evolution.
Artifacts only hint at the evolution of hominid minds. Insights into hominin mental descent may be gleaned by comparing humans to apes, where there are slight but telling differences.
The working memory of chimps outperforms humans. Superior memory withstanding, humans are better at mental visualization, such as seeing in the mind how objects may align. Nonhuman primates rely more upon haptic contact for problem-solving related to object manipulation. The human skill of using sight rather than touch facilitates tool construction and use. Children develop this ability at 3 years of age.
Many nuanced accounts of human evolution implicitly assume that biological changes must precede cultural changes. This prevailing logic in the field may put the cart before the horse. Take care to distinguish cause from effect. Supposedly momentous changes in our genome may sometimes be a consequence of cultural innovation. ~ English geneticist Simon Fisher
Brains & Brawn
Hominid aerobic capacity for endurance running improved 2 MYA. Around the same time, brain size showed a notable increase: a trend that accelerated during the Middle Pleistocene, 800 TYA. Also ~800 TYA, Homo began having longer adolescence, as contrasted to the more rapid development of earlier hominids.
The single biggest change of hominin evolution was in metabolic allocation: brains demanded more calories while muscles became more parsimonious. Ravenous brains developed by their becoming more molecularly complex and more intricately integrated.
Contrary to common conjecture, nothing suggests that hominid brain evolution improved acumen. Hypotheses about hominids progressing in problem-solving or sociality via brain changes are unsubstantiated. A trove of evidence dispels the notion that brain size or organization is related to intelligence. For instance, technology is not evidence of astuteness. With their industrial technologies modern men engineered their own extinction within a few generations. How smart is that?!
Oddly, larger brain size led to smaller guts. This life-history trade-off – enlarging the brain leading to a smaller digestive system – is common among fish, birds, and mammals. Why is not understood.
Typical consequences of larger brains are fewer offspring and greater altriciality. Primates have fewer offspring than other mammals, and humans fewer still.
As their brains got bigger, human muscles atrophied. For their size, monkeys and chimps are far stronger than even the burliest men.
There is more to the story than trading brawn for brain. In losing strength, hominin muscles adapted for a different power: endurance. Tellingly, walking is excellent mental exercise, as it demands sensory awareness.
Endurance allowed foraging over greater distances. It also engendered the diaspora that led to the human infestation of the entire planet.
Culture
Culture is not causeless and disembodied. It is generated in rich and intricate ways by information-processing mechanisms situated in minds. These mechanisms are, in turn, the elaborately sculpted product of the evolutionary process. ~ Jerome Barkow, Leda Cosmides, & John Tooby
Culture represents shared symbolic expression: an exhibition of abstraction in a social context. The earliest hominids had culture; just as other social animals do.
Culture shaped hominids. Early on, hominids shed the sharp, pronounced canine teeth which apes use as a threat signal. Faces became more expressive.
Humans are the only primate with easily seen sclera (whites of the eyes). When this happened in hominin evolution is not known (as no fossil record exists of such soft tissue), but is indicative that subtle, nonverbal communication became significant in the cultural repertoire.
Spontaneous smiling – an expression of joy – is a universal human expression with cultural implications. Typically, too much smiling is interpreted as a sign of shallowness or dishonesty. As something of a mask, Japanese sometimes smile when angry or confused. Other Asians may smile when embarrassed or to cover emotional pain.
Another universal look is a face contorted by anger. Despite never having seen one, even blind children can make an angry face. Lowered brows, flared nostrils and a piercing gaze define the face of anger. 7 key muscles groups work in concert to produce the look.
Anger evolved to motivate effective bargaining behavior during conflicts of interest. Humans are exceptionally good at assessing fighting ability just by looking at someone’s face. The explanation for evolution of the human anger face is surprisingly simple – it is a threat display. ~ Australian criminologist Aaron Sell
The anger face evolved as a show of power. People with angry faces appear more formidable.
Stronger men anger more easily, fight more often, feel entitled to more unequal treatment, resolve conflicts more in their own favor and are even more in favor of military solutions than are physically weak men. ~ John Tooby
When push comes to shove, human sociality comes down to might makes right. It is the most archaic evolutionary rule of conspecific relations and shows how human culture has not strayed from it biological base.
People who are judged to be stronger tend to get their way more often, other things being equal. ~ Aaron Sell
The emotional stature of apes and humans is identical. Simians have an innate capacity for empathic kindness, as do many other animals. Conversely, when provoked, chimpanzees have a capacity for savagery that is positively manly.
A significant aspect of culture is self-control, and the degree to which its loss is tolerated by others. This facet of culture strongly influenced the sociality of hominids, especially regarding social cohesiveness and conflict.
Cooperation among apes is impeded by male social intolerance. This same lack of comity would haunt hominids, as is apparent in the pettiness of modern politics.
Language
Language is a system of symbols (syllables, words) with interrelated meanings (semantics). The structural rule set that establishes context is termed syntax.
Grammar is overarching and regards the proper use of language for a certain culture milieu. Grammar includes semantics, syntax, punctuation, and spelling.
Language facility is innate and communication universal among all life. All life forms have their own languages to communicate with conspecifics. We understand little of the syntactic subtleties of other life.
Human language syntax arose from preexisting systems in other species. ~ Japanese linguist Shigeru Miyagawa et al
The genetic basis for song production in birds, vocalizations in mice, and human speech are the same. Birds learn to sing the same way that babies learn to talk.
Gibbons sing by the same process that humans use to produce speech. Singing gibbons naturally croon with a virtuosity attained only by women opera sopranos.
Humans musicality is closely related to language facility. Both involve melody and measure. Pitch and rhythm are crucial cues to language comprehension.
Tilda
What we have to do is discard this old idea that apes are simply incapable of doing anything remotely similar to human speech production. ~ American zoologist Rob Shumaker
Tilda is an orangutan born in Borneo in 1965. She was captured young and has spent most of her life among humans. Tilda’s early years were as a circus animal, before finding a home in a zoo.
At some point Tilda began imitating people. She waves her arms and shakes her head the way humans do; and she whistles – something wild orangutans don’t do.
Researchers took an especial interest in Tilda because of her whistling. Then she surprised them with faux speech: gibberish words, though following the patterns and pitches used by humans.
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Chimpanzee bonding involves much contact: the time-consuming task of grooming. In 1997, English anthropologist Robin Dunbar proposed that hominin vocal language arose as a “cheap” means of social grooming. Alas, Dunbar knew too little zoology. Many animals stay in touch with friends at a distance by chatting with them.
Animals respond to each other’s vocalizations to maintain their social bonds. ~ American zoologist Ipek Kulahci
That other animals fulsomely communicate does not counter Dunbar’s conjecture of human chat as cheap grooming. It instead places the evolution of vocalization as an adaptive continuum in human descent.
Amphibians, reptiles, and mammals all have larynges which function to preclude food aspiration and facilitate sound production. Vocalization did become increasingly important in Homo: the modern human larynx adapted as recently as 40,000 years ago to allow faster talking.
The basic syntactical knowledge upon which all human languages are based is inborn. By 3–4 months, infant vocalizations express a full range of emotions. Language learning is a process of vocal attunement and attachment of symbolic meaning to sounds.
People expeditiously bond via vocalization, develop conditional relations, and express hostility. Gossip has long been the lingua franca of sociality.
Language is very much a social tool. Not only does it allow us to exchange information relevant to our ability to survive in a complex, constantly changing social world, but it also allows us to mark other individuals as friend or foe. ~ Robin Dunbar
The relative position of the larynx tends to be lower in men than women. This gives males deeper voices at the expense of the larger range of discrete vowel sounds that females can produce.
People size each other up by the quality of their voices. As with other animals, deep voice exaggerates size.
Like stags, men evolved deeper voices to deter sexual competitors. A confident man expresses his sense of dominance by speaking at a lower pitch. Conversely, submission squeaks.
Low-pitched male voices signal masculinity. Women more easily remember information when told by a man with a deep voice.
The languages developed depended partly on climate. Whereas languages with tonal floridity developed in humid areas, those with simpler tone pitches emerged in drier regions.
Tonal languages, such as Chinese, are only possible with adequate humidity, which keeps the mucous membranes moist, allowing more elasticity. Humidity also improves the ion balance within the mucous membranes of the vocal folds, affording greater precision in pitch oscillation.
Compared to chimps, humans weave language into a more complex social fabric. This is an alloyed advantage. For one, liars have to keep their stories straight. In contrast, chimp deception is simpler and less frequent.
Monogamy
The emergence of pair-bonding in humans was a major evolutionary transition, which dramatically altered the trajectory of our species. ~Russian evolutionary biologist Sergey Gavrilets
Although common in birds, social monogamy is rare among mammals. 90% of birds live in pairs, whereas less than 3% of mammals do. The demands of mammalian motherhood – internal gestation and lactation – make it advantageous for males to seek other mating opportunities.
In mammals, social monogamy evolved when females were largely solitary, and the ranges of roaming male overlapped those of several females. Female solitude partly descended from diet.
Pair-bonding arises in species that diet on high-quality foodstuffs which are not abundant. Fruit is the main part of the diet in 91% of socially monogamous primates, whereas only 28% of solitary primate species rely upon fruit. Foods with low nutritional content are a much larger part of solitary species’ diets than monogamous primates.
When breeding females are intolerant of each other and female density is low, males cannot guard more than one breeding female. This logistical pickle produces monogamy.
Where females are widely dispersed, the best strategy for a male is to stick with one female, defend her, and make sure that he sires all her offspring. In short, a male’s best strategy is to be monogamous. ~ English zoologist Tim Clutton-Brock
Primates are unusual among mammals in that monogamy evolved independently in all major clades. In primates, larger brains produced a more prolonged infancy. This meant that mothers were infertile for longer durations.
Killing a female’s babies brings her back into fertility. There are only few ways to evolve a prevention to this reproductively self-defeating dilemma.
Female chimps mate with many of the males in their group to confuse paternity. This spares them from infanticide.
The descent of hominins – with their enlarging brains, cunning, and often violent nature – rendered infanticide an evolutionary dilemma, especially with the lessening of tightly-knit social bonds. The adaptive solution was pair-bonding.
You do not get monogamy unless you already have infanticide, and you do not get a switch to paternal care if you don’t already have monogamy. ~ English anthropologist Christopher Opie
There is no biological imperative to monogamy in humans, even as men with small testes are more inclined to parenting. Instead, mate bonding is a cultural norm.
Only 17% of human cultures are strictly monogamous. The others involve a mix, with most people practicing monogamy, either heterosexual or homosexual, while a minority practice polygamy or otherwise. Even in those cultures with monogamy, extra-pair copulation is common.
The human mating system is extremely flexible. ~ Canadian anthropologist Bernard Chapais
Over 90% of bird species breed as monogamous pairs. In 90% of those birds, extra-pair paternity is common. Though the numbers are likely lower, similar dynamics applied to hominins.
From social insects as well as birds, cooperation is unlikely to evolve within extended families unless there is also genetic monogamy. A different form of cooperation – between unrelated individuals – may actually be promoted by promiscuity. ~ English zoologist Ben Sheldon & American zoologist Marc Mangel
Mothers are devoted to their offspring. A father’s commitment to paternal care depends upon paternity. Extra-pair mating by females creates an incentive for males to cooperate with neighbors. Infidelity likely was instrumental in extending male hominin sociality.
Where maternity certainty makes females care for offspring at home, paternity uncertainty and a potential for offspring in several broods make males invest in communal benefits and public goods. ~ Norwegian zoologists Sigrunn Eliassen & Christian Jørgensen
Longevity
As a life-history variable longevity has served humans especially well. Extended childhoods not only encourage brain development, it also knits families and communities closer together, as altricial youngsters need resources and protection for greater durations.
Living longer garnered the greatest advantage that a social species given to technological innovation could have: the benefit of experience.
Groups of gregarious mammals are commonly led by elders. Elephants and cetaceans are exemplary. Their knowledge of foraging techniques and prime feeding locations can be the difference between group survival and demise.
The experience edge can be particularly telling in territorial concerns, whether defending or taking new lands. Wolves are predators whose prowl is determined by dominion. Taking territory from another pack is largely a numbers game, but experience tips the balance beyond numbers. Packs with grizzled veterans battle better for territory.
Being physically past their prime, brawn is not the contribution that old wolves give to a brawl. It is instead imparting improved combat tactics to their packmates.
Social Cunning
According to the social intelligence hypothesis, social context represents an important force driving the selection of animal cognitive abilities such as the capacity to estimate the nature of the social relationships between other individuals. ~ French zoologist Clémentine Vignal et al
In an ersatz interpretation of the social intelligence hypothesis, that human cognitive abilities evolved via intense social competition has been suggested. According to this notion, effective strategies of achieving social success – alliance formation, manipulation, exploitation, and deception – translated into reproductive success.
The social brain hypothesis implies that constraints on group size arise from the information-processing capacity of the primate brain. ~ Robin Dunbar
In 1992, Dunbar figured that hominins evolved bigger brains because they lived in larger social groups than other tailless primates. (The premise of the social brain hypothesis is ridiculous because Dunbar’s assumption that brain size relates to intelligence is false.) He calculated that 150 people – Dunbar’s number – has long been the mean size of cohesive human social groups.
In 2000, American anthropologist Russell Bernard and English social network researcher Peter Killworth nearly doubled Dunbar’s number, to a mean 290 (median = 231, owing to a distribution skew), based upon numerous field studies. Dunbar’s number remains better known.
Dunbar’s social brain hypothesis was premised on ignorance of other species, beginning with apes. Further, such group statistics miss a major facet of human social complexity.
The difference between ape and human societies comes by way of cultural elaboration and economics, not just numbers. Hominin propensity to problem-solving as a rewarding exercise in of itself, coupled to cultural transmission, rendered technology cumulative. This, combined with the will to dominate, drove the economics and polities politely termed civilization.
Humans, chimpanzees, dolphins, and elephants live in fission-fusion social groups: communities of up to a few hundred individuals, with dynamic subgroups that include families, friends, and coalitions. Everyone in a community recognizes one another. Each member has a relationship with most every other in the group; hence matrices of bonds exist. Though similar in essentials, the societies of monkeys, chimps, elephants, and dolphins are generally more close-knit than that of people. This statement has become truer since industrialization and burgeoning human populations.
Mammals are not the only animals that live in communities where individuals know each other, with social hierarchies, or where there is an audience effect to an animal’s behavior. The pressures of society press upon microbes, plants, insects, fish, and birds much as they do mammals.
The particulars and levels of sophistication vary, but the thrust of the social intelligence hypothesis applies throughout the realm of life. What little we know of bacterial sociality indicates a variety of interactions, both competitive and cooperative.
As with other animals, social demands on a variety of fronts, both direct and indirect, affected hominid evolution. Being able to remember more relationships would not have advanced culture or technology, which was key to humans coming to take their fates into their own hands. Machiavellian maneuvers would have proven sorely inadequate.
Man in many respects may be compared with those animals which have long been domesticated. ~ Charles Darwin
Domestication has historically emphasised special behavioural qualities that we share with domesticated animals, such as social tolerance and low emotional reactivity to provocation. Anatomical changes found in H. sapiens compared with earlier hominins show a strong similarity to those that occur in domestication. “Domesticates” mostly have smaller bodies than their wild ancestors. Their faces tend to be shorter, projecting relatively less forward. Differences between males and females are less developed. And domesticates usually have smaller brains. The differences between modern humans and our earlier ancestors look like the differences between a dog and a wolf. ~ English primatologist Richard Wrangham
Cooperation
Complex social organization builds on the emergence and maintenance of cooperation. ~ German cognitive ethologist Julia Fischer
Although avarice and lust for power by men propelled exploitation on a grand scale, it was cooperation, not competition, which permitted human civilization to blossom. An ample measure of collaboration was essential in building the empires of early civilizations. Without cooperation, humans would have never emerged from the Stone Age. They may not have even got that far.
Spontaneous, altruistic behavior is exclusively found among species where the young are not only cared for by the mother, but also other group members such as siblings, fathers, grandmothers, aunts and uncles. ~ Swiss anthropologist Judith Maria Burkart
The family of New World monkeys known as callitrichids – marmosets and tamarins – cooperatively care for their young. Alloparenting is by no means confined to primates. Meerkats cooperate to rear their young. As seen in the tropical rainforest, even some spiders practice protective alloparenting.
The adoption of cooperative breeding by our hominin ancestors provides the most parsimonious explanation for the origin of human hyper-cooperation. ~ Judith Burkart et al
For hominids, cooperation as a social norm required comity among adult males.
Our ability to effectively collaborate with others is largely responsible for what our species came to be. ~ Sergey Gavrilets
Hominids were not the first instance of male-male cooperation in simians that afforded development of complex multilevel societies. Guinea baboons are the only species of baboon where males are tolerant and cooperative toward same-sex conspecifics, even those that are not related. Physical traits associated with sexual competition, including the size of canine teeth and testicles, are smaller in male Guinea baboons than in other baboons. Male Guinea baboons have less rivalry and are less aggressive toward females. Males actively contribute to the cohesion of their multilevel society, as contrasted to the energetic efforts by males in other baboon species in maintaining dominance hierarchies.
If prehistoric people began living closer together and passing down new technologies, they’d have to be tolerant of each other. The key to our success is the ability to cooperate and get along and learn from one another. ~ American biologist Robert Cieri
Modern humans appear in the fossil record ~300 TYA but it was only 50 TYA that saw an upsurge in art production, technological innovation, and cultural exchange. Contemporaneous with the upswing in culture human testosterone levels declined. Facial structure reflected the change. A heavy brow and larger upper face were replaced by a less prominent browline and rounder face.
A similar transition happened with aggressive chimpanzees and their peaceable descendants: bonobos. These 2 apes have distinct developmental paths, and they respond to social stress differently. Male chimpanzees experience a strong rise in testosterone during puberty. Bonobos do not.
When stressed, the bonobos do not produce more testosterone as chimps do. Instead, bonobos produce more cortisol, the stress hormone. Chimpanzee and bonobo faces differ.
It’s very hard to find a brow-ridge in a bonobo. ~ American evolutionary anthropologist Brian Hare
Though bonobos are humankind’s closest ape relative (not chimpanzees, as long thought), men are no peaceful bonobos; quite the contrary. Advances in hominin cooperative sociality doubtlessly owe to the leavening influence of females, with their superior social skills and relative sense of harmony.
It was women, not men, that were key to human social advance. The shift from male-dominated, female-dispersal groups to pair-bonding and greater sexual egalitarianism provided the context for expanded social networks and alliances among unrelated individuals. The transformative context was female interaction that fostered social stability, collaboration, and cumulative culture. Men went along with what their women persuaded them was advantageous: teamwork.
There is a dissonant irony in hominin sociality that remains on display to this day. Men somewhat reluctantly cooperate, doing so only when self-interests coincide or within the context of a dominance hierarchy. All social coalitions involving men have a pecking order. Male-dominated inter-group tension is a norm, tempered only by power assessment and fear of material or social status loss.
Lethal raids by competing groups were part of life for hunter-gatherer communities. ~ Argentinian paleoanthropologist Marta Mirazón Lahr
The self-conflicting gyre of conflict/cooperation reflects the evolution of human sociality. The social bonds of tribes and dominance regimes of early humans were forged by war: one group pitting itself another for spoils, including fertile females.
Effective defense against marauders demanded collaborative efforts, so they emerged. The strongest bonding experience for men is facing combat together.
Collaborative ability is more likely to evolve first by between-group conflicts and then later be used against Nature. ~ Sergey Gavrilets
Social Structure
Most primate societies are independent, single-group structures. In contrast, human sociality involves multilevel, nested alliances.
Close-knit mixed-sex nonhuman primate groups last only until sexual maturity. To avoid interbreeding either males or females emigrate to another group.
In contrast, humans remain familial into adulthood. Pair-bonding between families created affines (in-laws) that extend group cohesion. This created kin-based interlocking bonds between groups, forming the basis for tribalism that still comprises the core building block of human social structure. Upon this larger societies were built. Further social glue was applied with shared culture and aligned economic interests.
Domestication & Violence
While warfare has been a constant in human affairs, a countercurrent has been the domestication of humans. (In modern bureaucratic parlance, domestication is called institutionalization.) Much as domesticated animals are bred for passivity, the innate aggressiveness of male human stock has been tempered by killing off some of the most violently inclined. Wars helped somewhat in that regard.
More generally, sustained violence is frowned upon in most cultures, and in modern times has been claimed as a monopoly of the state. Suppression and sublimation of aggression are typically encouraged by ruling elites, who fear that violence unchecked may come to be turned against them.
Thus, strong cultural norms subdue innate male propensity to violence. Nonetheless, as a glance at the daily news on any day reveals, civility remains a limited commodity. Violence, whether physical or economic, is a fact of everyday human experience.
Technology
Tools weren’t just a product of human evolution, but actually drove it as well. ~ American paleoanthropologist Thomas Morgan
The evolution of hominin symbolic thinking had its practical turn with engineering, which welded observation and theorization to application. The initial impetuses for hominid engineering were getting enough to eat and surviving inclemency. Engineering impulses broadened to create art.
Cultural evolution strongly depends on population size. ~ French paleontologist Maxime Derex et al
Thanks to societal stability, engineering became a self-perpetuating gyre, succored (or stymied) by culture. Technology engendered cooperation and materialist culture, both essential to further technological development. Symbolism, technology, culture, economics, and social value systems became entangled in constructing civilization.
