The Human Story, Robin Dunbar, 2004

 

dunbar

 

 

There are about 150 sites of prehistoric cave art in Europe concentrated in the southern france and spain.

Cave art is the final flowering in human evolutionary history – the upper Paleolithic revolution. It began 50,000 years ago with sophisticated stone, bone and wooden tools. From 30,000, explosion of art work (carved button, brooches, dolls, toy animals, the so called Venus). From 20,000 deliberate burial, music and “life in the mind”.

6 to 7 million years ago, separation from the African apes.

Laetoli in northern Tanzania: a 50m of track way preserved under layers of cold ash. Often interpreted as the ancestral family foot print (mum, dad and youngster), the reality is that they were certainly part of a larger group.

Darwin’s view: he argued that evolution was not linear and progressive but, rather, more like a branching tree.

Ape like family divided into 2 distinct lineages some 15-20 million years ago : Orang Utan on one side (Garilla, Human, Chimps, Bonobo) on the other.

Today’s African apes seem to appear out of nowhere: there are no species in the fossil record of the last 5-10 million years related to them.

The structure of genetic code change over time: because of imperfection in the way DNA copy themselves during the course of reproduction. Since the rate at which these hidden changes occurs is roughlty constant across time, the number of difference between 2 individuals represents a rough measure of the amount of time since they last shared a common ancestor.

Current estimate for the last human-ape ancestor: 5-7 million years.

So close was the relationship between humans and chimpanzees (we share 98.5% of our DNA) that it seems we were really just chimpanzees gone mad.

Bipedalism predate by several million years the very earliest beginnings of the dramatic increase in brain size and tool use that was to lead ultimately to modern human. Older theories tended to see our large brain, bipedalism, hunting and technological skills as all being part of the same adaptative complex. In fact these traits evolved over a period of several million of years.

Bonobos look more human as the have slightly longer legs than is typical of the other two African apes.

True striding bipedalism appeared only with the homo erectus around 2M year ago.

Once the human brain started its rapid increase some time from around half a million years ago, the problem of giving birth to baby with large heads became more acute.

Our ancestors opted for an alternative solution: they reduced the length of pregnancy. In all mamals (except humans) the length of pregnancy is determined by the size of the species brain. Birth is the point at which the brain reaches its adult size (if we were to do the same, pregnancy would last 21 months). In humans the brain growth continue after birth.

With the appearance of the first members of the family home around 2M years ago, we see the beginnings of a rapidly accelerating increase in brain size. Even so it is not until the appearance of our own species, home sapiens, around half a million years ago, that this acceleration really begins to take off. With Neanderthal that brain size achieves its greatest volume.

Homo erectus 2M years ago, spread from Africa to the rest of the world: improvement in the range and quality of tools (more deliberately shaped hand axes). But after that, stone tools remain all but changed for 2M years, despite the fact that the brain doubles in size over the same period. The big change occurs recently, 50,000 years ago, roughly 100,000 after the human brain reaches its modern size. The change is sudden – often described as a revolution.

We might be better advised to see the history of our species as one of increasing degrees of humanity. Around 500,000 year ago one of the African population of homo erectus began to undergo a rapid evolution towards larger brain size and lighter body build: homo sapiens. It spread into the Near East and Europe replacing the populations of H. erectus which is known as archaic humans (homo heidelbergensis). Around 200,000 years ago, a lighter more gracile variant evolved and spread with remarkable speed (the anatomically modern human AMH) and replaced older archaic human populations in Africa, entering the middle east 70,000 years ago, reaching Australia 60,000 years ago and backtracking to Europe 40,000 years ago and reaching North America 15,000 ago.

All the 5 billion humans alive today descend from a small group of 5,000 female ancestors who lived 150-200,000 years ago.

Neanderthal fossil record is one of the best we have with more than 270 individuals. Neanderthal’s DNA lies well outside the variation seen in modern human. They could not have been the ancestors of modern Europeans. Neanderthals represent the descendents of an early migration out of Africa into Europe by archaic Homo Sapiens.

Disease remains a distinct possibility as an explanation of the disappearance of the Neanderthals, especially given that the hot humid tropics of Africa from which the Cro-Magnons had originated are a veritable breeding ground for disease.

As the last Ice Age bit deeply into Europe, so Neanderthals living sites moved southwards. Global temperatures during this period fluctuated widely from one decade to another, so it is possible that Neanderthal found themselves caught out in the wrong place. The resulting attrition would have put any species under very considerable demographic pressure and made it difficult for it to recover.

This suggest perhaps a cultural difference of some sort, the most obvious being the use of clothing, since the use of both cave shelters and fire were well known to the Neanderthals.

Theory of mind: adult humans have an absolute upper limit on the levels of intentionality that they can cope with at about 5 or 6 orders (Shakespeare) : Peter believes -1- that Jane thinks -2- that Sally wants -3- Peter to suppose -4- that Jan intends -5- Sally to believe -6- that her ball is under the cushion. The limit for most people is about 4th to 5th order.

Chimpanzees in test do as well as 4 years old children, children who are just on the brink of acquiring theory of mind.  If chimpanzees have theory of mind it seems that at best they can only aspire to 2nd order of intentionality. Dolphins also failed to pass.  Perhaps it is not that they cannot do theory-of –mind tasks, but that they cannot figure out what the point of this particular game is, irrespective of whether it reauires theory o fmind to solve correctly.

Chimpanzee have the ability to take another’s perspective. This is not theory of mind but a major step in the right direction.

The ability to step back from the immediacy of the world may be crucial in allowing is to assess the consequences of alternative courses of action.

Social group size in primate correlates with the relative size of the neocortex of the species concerned. In mammals the sheet is typically 10 to 40% of the brain volume. In primates it starts at 50% and rises to as much as 80% in humans: this suggests it has been the need to manage complex social world that has driven the evolution of larger brains. The bit that has increase out of all proportion in modern human is the frontal lobe (responsible for the much greater intelligence of apes and humans, active when we are engage in thinking about social cognition tasks). The sensory processing areas of the neocortex seem to increase in size less fast than the non sensory components in the frontal lobe.

If we map the intentionality levels of monkeys (1st), apes (2nd, just) and modern human (5th) onto the relative size of the their lobes we get a straight line. This suggest Homo erectus brain size, 2M year ago,  would have reach 3rd order of intentionality and 4th order of intentionality is reached 500,000 with archaic homo sapiens. Neanderthal and cro-magnon had brains large enough to accommodate 5th order of intentionality. The 5th order came on the scene a mere 200,000 years ago.

1980s chimpanzees in the Gombe park deliberately set out on raiding expedition in to the territory of the neighbouring Kahama community and wreack a terrible punishment on their victim. It last months until every one of the 6 males of the Kahama community had suffered the same fate. They all died of the their wounds. Kahama males had all originally been members of the Kasekela community but had moved out to establish their own territory next door only a few years previously. They were all individually well known to their killers.

“the by now increasingly alarmed gorilla suddenly realizes that gravity and the steepness of the hill slope have conspired to deprive him of all capacity to stop”

It is unquestionably true that bonobos exploit the opportunities offered by sex to defuse tense social situations as well as to bond with friendships with each other.

Monogamy is a rare form of social arrangement among mammals.

A displaced male never gets the chance to breed again. But whether or not such an attack is successful depends entirely on the majority of females being willing to desert their former male for a new one.

The maternal instinct seems to be triggered as part of the hormonal restructructuring that is brought about by the birth process itself. A nice example of how hormonal and emotional processes interact with cognition to achieve essential biological objectives (responding to the baby need of care and attention).

Because male mammals who acquire a pregnant or lactating mate will be unable to reproduce for some time, infanticide has been widely documented in all the mammals, but especially primates.

Among the Ache hunter gatherers of Paraguay, adults average around a dozen partners over the course of a lifetime, with each partnership lasting from a few months to several years – a situation that may not be untypical of human hunter gatherer societies where formal marriage do not exits.

Hypoglossal canal, a hole at the bottom of the skull that the nerve to the tongue passes through. The larger it is, the bigger the nerve and the amount of work it has to do. All fossil hominids after the appearance of archaic humans (first homo sapiens, 500,000 ago) have hypoglossal canals that are similar in size to those modern humans (including Neanderthals and Cro-magnons): the transition happened between 2m and 300,000 years ago (all australopithecine skulls have ape-sized holes.  Modern humans – but not apes – have a dramatic enlargement of the vertebral canal in the region of the thoracic vertebrae in the upper chest – the nerves from this region control the chest muscles and are important to fine control breathing that is necessary to produce speech. Homo erectus has thoracic vertebral canals that are no larger than those of monkeys/apes. Neanderthals have the same as modern humans. They must have heritated this from the most recent ancestor Homo sapiens, around 500,000 years ago.

Experimental studies of monkeys have confirmed that grooming triggers a release of endomorphins.

So how do we create bonds of intimacy with those with whom we do not wish to have sex at the drop of hat? The answer, I am going to suggest, is that we make them laugh. Laughter seems to be a good releaser of endorphins. It seems that at some point during the course of human evolution, we borrowed the chimpanzee playface and its vocalisations and exaggerated them to provide the reinforce for grooming at a distance.

The deeply emotional stirrings generated by music suggest to me that music has very ancient origins, long predating the evolution of language (music centre is in the right hemisphere, language center in the left hemisphere).

One beautiful exemple carved flute from deer bone was found in a cro-magnon debris field in France, dating from 30-40,000 years ago.

The oldest recorded spear is a length of wood hardened in a fire founc in Clacton in southern England, dated to 400,000 years ago.

If we compare the chimpanzee’s tool kit of a dozen or so documented items against the toolkit of least technologically advanced human cultures, they do not come out quite so badly.

For earlies stone tools, 2m year ago, on shape and wear patterns alone, we might question whether we can be absolutely be sure that the ones in the fossil record were really created of used by hominids and not by apes.

It took two years for Japanese macaques to learn to potato wash: this slowness makes it seem unlikely that they were simply imitating what the other did. It makes more sense if what they were actually doing was figuring out the solution to the problem for themselves.

It is the speed and facility with which human children leanr to copy what they are shown that is so impressive. The process is more laborious for apes.

Young chimpanzees seem more proactive and clued in to finding things out for themselves. This contrast is a bit of a puzzle really…

Every human tribe has some form of belief in a spirit world most (but maybe not all) have some sense of an afterlife.

Persistent low level stress on the body is particularly effective at stimulating the production of endomorphins. Religious practices seem as though they are designed to give us that opioid kick that makes us feel so much better able to cope with the vagaries of the world and at peace with our neighbors.

Carefully orchestrated mental practice (develop by mystics in all religions) allow adepts to disengage a bundle of neurones (above and behind the left ear). These neurons release a series of impulses leading to a shut-down of the spatial awareness bundles, generating a burst of ecstatic liberation  in which we seem to be united with the “infinity of being” and a flash of blinding light. This bundle of neurones is called the “god spot”.

The experience of mystics seems similar to what happens during near death experiences. The later are thought to be the result of oxygen starvation to the brain. Mystics may have discovered ways to induce oxygen starvation to the brain, perhaps even selectively to particular key areas of the brain.

The role that religion may play in providing the sense of community and belongingness (similar to the role played by families) is surely obvious. A religious sense may have evolved to facilitate the psychological bonding of extended family groups in which we have spent most of our evolutionary history. Religion probably evolved because it was such a good mechanism for bonding social groups and making them work together.

Religion has a modestly ancient origin that has little to do with the cultural diversity that has emerged in the last 30,000 years. Eurasian and African branches of modern humans were united until 70,000 years ago.  So the common root of religion must lie between 70,000 and 200,000 the last common ancestor of all modern human.

Earliest uncontroversial burial comes from Cro-magnon, 25,000 years ago (Dolni Vestonice) with a sense of an afterlife with the need for the accoutrement of everyday life to ease their way.

Although the neanderthals graves are often in a fetal position, a more prosaic explanation for this might simply be the desire to dig the smallest possible hole for the disposal of the body.

Neanderthal may not have developed religion: much of the brain extra volume was in the visual areas at the back of the brain, with proportionally less in the frontal lobe. With smaller frontal lobe, their achievable levels of intentionality would have been lower. Perhaps low enough to preclude the development of full-blown communal religion.

Some tribes do not have the concept of an afterlife (San, Masai)

The trance like state (with associated images of a world beyond the world) originating from communal bonding, music and dance is a powerful personal experience. Being led by an adept create the sense of security needed to develop a strong bond between the adept and the newcomer. In terms of origins of religion, the story I have sketched out here suggests that the earliest stages may well have been personal and intimate. Only later the intellectual advantage of religion have become evident.