Tuesday, February 8, 2011

Before The Dawn: Recovering the Lost History of Our Ancestors

Book Review: Before the Dawn: Recovering the Lost History of Our Ancestors by Nicholas Wade  (Penguin Books 2006)

This is a wonderful book and I think everyone would do well to read it. Basically it is about the history of our human species especially as indicated and informed by recent advances in the science of genetics. It is rather amazing that we can use genetics – not only of humans but also of humans’ animal companions and human parasites such as lice, to date (roughly) when things certain novel happenings such as when humans first made and wore clothing.

Scientists think humans evolved from an ape society in Africa that existed 5 million years ago. Also evolving from these primates are thought to be chimpanzees and their cousins bonobos. Much is discussed about this deep past and what factors may have led to divergence and development of our species. Homo habilis used stone tools 2.5 mya then with the development of homo ergaster around 1.7 mya the ape-like humans are thought to have lost their fur and presumably after this their skin darkened to protect from the African tropical sun especially as humans departed from strictly forest living of apes. Ergaster began to eat meat and herbs and tubers as well as the predominant fruit eaten by previous species. This sparked genetic changes in body size. Ergaster may have been the first human species to lose its mammalian hair – possibly as a need to sweat in order to cool itself and its larger brain. It is thought that skin was pale when there was still hair and when the hair was lost the skin mutated to a darker form in order to prevent loss of folic acid – an important nutrient. Geneticists pinpoint this happening around 1.2 mya based on silent mutations of the melanocortin receptor gene. Much later on as humanoids made it north out of Africa, the skin mutated back to a paler form possibly as a result of the need to absorb more Vitamin D in the colder environment with less sun. The ability of our head hair to grow very long (as opposed to apes and chimps who don’t grow long hair) is dated by genes to about 200, 000 years ago. There may be social reasons why this mutation occurred.

It is thought that groups from homo ergaster left Africa around 1.7 mya and developed into the archaic human forms of Neanderthal and Homo erectus while our ancestors, who would later become homo sapiens sapiens, remained in Africa until about 65,000 to 50,000 years ago. African Middle Stone Age peoples from 250,000 years ago to 50,000 years ago are thought to have had social networks, buried their dead, and collected pigment. They began to attain contemporary skull size and skeleton about 200,000 years ago and by 100,000 years ago everyone had this general size so this is when scientists postulate that there were anatomically modern humans. Behaviorally modern humans are thought to have come later around 50,000 years ago. This is the general time period when our homo sapien ancestors are thought to have left Africa, language began to develop in earnest, and with it stronger networking, the capacity for trade, religion, and advantage over other humans without these attributes.

There is some interesting discussion of the development of language. Some think that early language developed from sign language and grunt sounds to limited vocabulary (as in pidgin languages) with syntax coming later (as developed into creoles by children of those who spoke pidgins). Possible evolutionary pressures on language development are social bonding and/or sexual selection. Some think that dealing with new ecological niches away from Africa led to language development. The author states that Stephen Pinker of Oxford has suggested “that know-how, sociality, and language are three key features of the distinctively human lifestyle and that the three factors co-evolved, each acting as a selective pressure for the others.” Paleo-anthropologists seem to date language much early than archeologists. Archeologists suggest fully articulate modern language appears about 50,000 years ago. A language gene called FOXP2 was discovered and its latest upgrade which all humans have was dated to sometime after 200,000 yrs ago.

Next we have our ancestral human population emerging out of Africa, probably East Africa, at around 50,000 years ago. The group from which all humans except some in Sub-Saharan Africa are thought to descend from is a group of only about 5000 people or less. ‘... all men in the world carry a Y chromosome inherited from a single individual – the Adam of the Y chromosome – who lived in the ancestral human population. The same is true of mitochondrial DNA and the mitochondrial Eve.”

There is a mutation known as M168 that is present in all men who left Africa and some men in Africa. M168 can be dated genetically to have occurred between 40,000 and 90,000 years ago. 59,000 years ago is the estimate for when Y Chromosome Adam was alive. The dates for M168 coincide with when it is thought that the ancestral human population left Africa. In terms of mitochondrial DNA lineages:  “The mitochondrial genealogy of humankind has three main branches, known as L1, L2, and L3. L1 and L2 are confined to Africans who live south of the Sahara. The L3 branch gave rise to a lineage known as M, and it was the descendents of M who left Africa.”

On the earliest genetic branches of the human tree (L1 and L2) are two African peoples separated by half a continent of distance. The !Kung San in Southern Africa match to the L1 lineage and the Hadzabe of Tanzania match the L2 lineage. They must have split very far back in time. Interestingly, they both speak click languages (about 30 click languages are spoken in Africa). Language classifier Joseph Greenberg grouped the click languages as Khoisan. Click languages may be the earliest form of language. Linguists do not think that click languages can be learned fluently by those who begin with non-click languages – that they must be learned exclusively and from birth. DNA suggests that the San were once present in Ethiopia and DNA also locates people in North-East Africa who share ancestral paternity with the San. This reinforces that suggestion that the ancestral human population left Africa through the Gate of Grief near the Horn of Africa. This would have been about 2000 generations ago from now. Interestingly, many Khoisan speakers are said to possess a yellowish tint to their skin and eye features and others that suggest Asian features as well as Native American. Since they are thought to be an earlier DNA lineage it stands to reason that they would have the possibility of most all future peoples in their features. The !Kung San and a few others still live as hunter gatherers or foragers. They engage in small-scale warfare as well. It is thought by geneticists that when humans left Africa and entered different environments the evolutionary forces on them were greater than before and subsequent evolution continued at an accelerated rate and continues today. The whole notion that evolution stopped 50,000 years ago now seems very unlikely. Indeed, two new versions of genes that determine the size of the human brain emerged fairly recently, one about 37,000 years ago and the other about 6000 years ago. These gene versions (alleles) of microcephalin are thought to be related also to cognitive abilities. One wonders also why Upper Paleolithic Art was so well-developed in the caves of Southern France but not in other areas at the same time. Possibly there is a link to symbolical thinking advancement.

The exodus from Africa is thought to have brought the humans along the tropical coast lands of Arabia, India, Southeast Asia, and to Indonesia, and Australia – where aboriginal settlements have been dated to around 46,000 years ago. They were able to do this easier because of lower sea level due to water being locked up in ice sheets. A part of this journey would have required boats so based on this it is thought that man used them at that time, however primitive. For thousands of years people made their way towards Indonesia and Australia in a sort of wave of advance. Genetics indicates that these people lived in small groups that generally stayed in one area and did not mix with one another. There is genetic and archaeological evidence for this path of early migration. The Andaman islanders off the coast of India have features very similar to the pygmies in Central Africa, particularly short stature and protruding buttocks. This is likely due to an environmental factor of living in forests. Genetically they are in the M2 lineage that came from the early migration out of Africa. Though there is no direct evidence, it is likely that our ancestors who left Africa 50,000 years ago had black skin and features like native Australians. For the next 20,000 years it is thought that they were able to wipe out the earlier humanoid species: the lighter skinned Neanderthals and Homo erectus. 

Other topics covered are the pre-settlement period of the Upper Paleolithic from 50,000 to 15,000 years ago which includes the magnificent painted caves of Europe. Certain of the mitochondrial DNA lineages are thought to be better adapted to cold. These correspond to those that are thought to have crossed the Bering Straight into the Americans beginning around 14,000 years ago, although some geneticists and archaeologists think there could have been an earlier migration to the Americas, as early as 34,000 years ago. It is thought that there were two main later migrations, the last occuring about 10,000 years ago or later when the Eskimos and the Na-Dene speakers arrived in North America. According to linguist Greenberg the first group of three main language groups developed 583 of the 625 known Amer-Indian languages. Then came the Eskimos with their 10 languages and the Na-Dene speakers thought to have come from the Ket-speaking region of Siberia. There are 32 Na-Dene languages which include Apache, Comanche, and Navajo. South American tribes often show evidence of ‘genetic drift’ which suggests that their populations bred in isolation for thousands of years. Evidence of drift is a great indicator of this and an important shaper of genetics as is the more well known ‘natural selection.’

The origin of ‘mongoloid peoples’ is examined. This refers to the skull shape  and type of teeth possessed by many East Asians which first appears in the archaeological record about 10,000 years ago. Some have speculated this development to be a result of drift possibly in conjunction with natural selection as an adaptation to cold as groups may have been isolated by ice during the last glacial maximum. The epicanthic fold around the eyelids may be a similar adaptation. Humans may have developed black skin way way back as a way to retain folic acid and white skin as they migrated north in order to absorb Vitamin D. Wolves are thought to have been domesticated into dogs around 14,000 years ago in Siberia, coming to the Americas as well. Since dogs attach to masters they may have been an early possession of sorts for foraging humans who did not keep possessions until they began to settle. Dogs also likely helped the tribe by warning of attacks.

After the last glacial maximum the first human settlements appear around the eastern Mediterranean Levant around 15,000 years ago. These Natufians in Syria began to collect and process cereal grasses and later to collect seeds and initiate agriculture. It is fairly certain though, according to the author, that settlement preceded agriculture. “The Natufians also began a practice that became common in the ensuing Neolithic period, that of separating the skull from the body before burial. The corpses were buried but the skulls were covered with plaster, given new faces, and kept in the houses to serve as a close bond between living and dead.” Settled societies required a whole new set of cognitive skills involved with social status, ownership of property, surpluses and their result – trade, and specialized task development. Interestingly, a striking genetic change preceded settlement – the thinning, or gracilization of the human skull. Sheep and goats are thought to have been domesticated around 10,000 years ago in these settled areas. Lactose tolerance is thought to have developed due to cattle domestication, being particularly strong among northwestern European peoples.

The chapter on Sociality covers the dynamics of primate societies, warfare and cannibalism, the evolutionary basis of social behavior, the privatization of sex, and the evolution of religion. “Warfare is a bond that separates humans and chimps from all other species.” In some primitive hunter-gatherer societies skill and success in warfare confers reproductive advantage. Primitive societies were thought to be at war most of the time and nearly all would skirmish at least once a year. Often the objective was to ambush or do a dawn raid to get kills by surprise. Most evidence indicates that warfare was widespread everywhere among primitive societies and only began to lose potency in settled societies where economic benefits of trade began to outweigh the benefits of war. Thus was nurtured a more altruistic bonding between unrelated humans. The development of social behavior is a result of this tribal benefit. So we have a situation where reciprical altruism develops – ie. mutual back-scratching. The hormones of oxytosin (also used to induce childbirth) and vasopressin may be involved in the promotion of trusting behaviors among humans. Experiments have been done with oxytosin that suggests this is true. So a biologically likely genetic basis of trust is possible. Trust became more or less required in urbanized settlements and trade situations. It is thought that language and religion sort of co-evolved since language is generally needed to communicate religious ideals. These may have developed along with the reciprocal altruism discussed above. Some think that religion was a means to curb the misuse of language, a law or code per se. Religion set the stage for privilege and priesthood but also the needs of trade and economics set the stage for leadership and kingship and social stratification began to develop. “Religion, language, and reciprocity are three comparatively recent developments of the glue that holds human societies together. All seem to have emerged some 50,000 years ago.”  Pair bonding is thought to have significantly changed primate society. The privatization of sex among humans likely helped to reduce the unwanted consequences of male rivalry. The worldwide gracilization, or thinning of the human skull is thought to have begun about 40,000 years ago but occurred at different rates in different regions. Some geneticists have suggested that this is a genetic reversion to a juvenile form – where aggressive behaviors went out of favor so the preferred genetic form was one that became fixed before the aggressive behavior came – if I am explaining that right. The author suggests this is a secondary result of humans basically domesticating themselves. In many primitive human societies it is thought that up to 30% of males died through warfare. Now it is a mere 0.3% of all humans worldwide.  The next chapter discusses race as defined by genetic differences attributed to development in isolation to one another. Here race is classified by continental affiliation. By this method there are Africans, Caucasians, Asians, Pacific Islanders, and Native Americans. Genetic drift as well as natural selection has been very influential in making apparent the differences in race. Dominant racial characteristics can be generally identified through DNA analysis. The idea that race is really a social convention as put forth by some anthropologists (likely to correct attitudes of racism) is refuted by genetics, though it is very true that racial mixing is evident in many humans. It is true, though, that differences in appearance among the races are a result of a few selected genes rather than the many neutral ones we all share. The difference in genotype causes the difference in phenotype. But it is not just genetics but also environmental dispositions that cause differences in abilities so genes share the load of differentiation with geography. Genetic differences may account for differences in some abilities and in different dispositions in general.

The chapter on language attempts to classify all languages and show how they spread. Farming is thought to be a big factor. Sino-Tibetan languages are thought to have spread from the Rice Center in China and Afro-Asiatic, Indo-European, and Dravidian languages from the Wheat Center in the Fertile Crescent. Interestingly, of the 6000 known languages about 1200 of them, nearly a quarter, come from the Island nation of Papua New Guinea. Here people were still practicing forager lifestyles recently and were likely separated into this many groups. This observation suggests quite logically that a common language bonds people and increases trust and cooperation among them. The language models here tend to support Renfrew’s hypothesis of Indo-European languages spreading through farming but he does put forth the basic two hypotheses of whether IE languages spread by the plough or by the sword. Genetic studies indicate that a mere 15% of Western Europeans have a genetic relationship to Anatolians so the wave of advance model had to include more of the pre-existing European population than Renfrew thought. Genetics of 6000 year old skeletal remains in Britain were found to be very similar to those living in the same area today. As far as dating proto-languages, including PIE, the authors suggest much earlier dates than those usually given. These earlier dates are hinted at by genetic studies. Greenberg’s language families are covered. They are based on comparisons of 100 or so key words through all languages of the world with some interesting results. He classified languages into super-families that emerged in different times so in different time periods the super-families may have some different distributions. Apparently, Greenberg made some interesting discoveries of possible remnants of the earliest of human languages. One is an amazing similarity of words for number 1 and finger in languages throughout the world.

Finally, there a chapter on genome studies and tracing various ancestral heritages in historical periods and an overview chapter on evolution and the future of evolution. Disease prevention and treatment goes hand in hand with genetics as it is genetics that leads to predispositions to getting as well as getting rid of diseases. Perhaps the gracilization of the human skull and the increase in brain size will continue. Some argue for the benefits of directed evolution. On the other hand that may create speciation in which some have the genetic upgrade and others don’t which would create imbalances that many would consider unethical. Any initial directed evolution would likely be involved with disease prevention and mitigation one would think.

Anyway, this was a great book to read and ponder. My review is probably not very well written as I have presented lots of isolated facts, opinions, and observations. I just wanted to present some of the intriguing ideas.

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