The Journey of Man: A Genetic Odyssey (14 page)

My Y-chromosome is defined by a marker known as M173. What this means is that at some point in the past, a man – one person – had a change from an A to a C at a particular position in the nucleotide sequence of his Y-chromosome. This man could, in fact, be called M173, after the marker. All of his sons also carried this marker, marking them uniquely as his male descendants. They in turn passed it on to their sons, and over time it increased in frequency. Today, M173 is very common in western Europe, where my male ancestors come from – over 70 per cent of men in southern England have it, showing that we all have the same recent ancestor. But this is not the only marker I have – if I trace my genetic lineage back in time, I also have additional polymorphisms with names such as M9 and M89 – each one a unique change at a different position in my Y-chromosome sequence. I also have the marker M168, which places my ancestors, like those of every other Eurasian, in Africa around 50,000 years ago. The order of these markers allows me to trace the journey taken by my ancestors to the British Isles over the past 50,000 years – and exposes some fascinating relationships among people around the world. Of course, this same exercise can be repeated for every man alive today. It is a bit like deconstructing the bouillabaisse recipe passed to me by my parents and tracing back through each of the ingredient changes made by preceding generations to the ultimate source of the recipe – the original African soup.

We saw in the preceding chapter that one marker, M130, defines he majority of men living in Australia. It traces back to Africa, sharing a common ancestor with my Y-chromosome when we reach M168 – our Eurasian Adam. The limited distribution of M130 in populations around the world reflects its coastal journey out of Africa, skirting along the south of the continent, leaving tantalizing traces of the trip along the way. But were they accompanied by men carrying M89, the next marker on my lineage? Did the journey into Eurasia begin 50,000 years ago on the south Asian coast?

Before we can answer this question, and begin to dissect the Eurasian soup recipes beginning with M89, the ancestor of most non-African Y-chromosome lineages, we need to ask a vitally important question: if – as all of the archaeological evidence suggests – modern humans were present in Africa by 150,000 years ago, why did they wait so long to leave?

The sun is going down on the east African savannah and it is starting to get noticeably colder. You shiver, relieved that you and the other members of the hunting band managed to kill a lame gazelle. The clan will eat well tonight. When you return to camp, everyone takes a simple stone cutting tool – sharp on one edge and blunt on the other – and butchers the animal. The tool, which anthropologists today would classify as Mousterian (Middle Stone Age), is simple but effective. You make quick work of the sinew and bone and soon you are relaxing around the fire, watching the meat cook over the flames. A hyena howls in the distance and you begin to think about other things for the first time in hours.

As you mull over the day’s hunt you are thankful that your luck has held out again – the animal herds do seem to be getting sparser. Of course you don’t know it, but the African climate has been getting drier, and the resources to support the herds are simply not as common as they used to be. After dinner your mate brings your son to you. Although he is a strong, healthy child, he worries you because he seems so unlike the other children. For one thing, he has already learned to speak – at age two – while the other children do not do this until they
are at least three. He also seems to be much better at making things than the other children in the clan, and enjoys playing games with the small pieces of stone that lie scattered around the camp. He seems much more emotional than the others, often erupting into violent temper tantrums that scare the other clan members. The strangest thing, though, is that he has begun to trace images in the dust that are similar to the animals that you bring back to camp. You find this especially frightening, and quickly rub them out when you see them. Others in the clan have noticed, though, and there have been some mutterings about his unusual behaviour.

Time passes. As your son grows up you teach him to hunt and make simple tools, hut his knowledge soon surpasses yours. He seems to have a magical ability to anticipate what the animals will do, which makes him a popular member of the clan, in spite of his odd behaviour. At an early age – around fifteen – he becomes the accepted leader of your small group. Under his guidance your clan eats well and prospers. He fathers many children, and they too seem to be much cleverer than others in the group. Within a few generations all of the members of the clan can trace their ancestry to him. He becomes the ‘totemic ancestor’ of the group – the founding father – and everyone descended from him is by definition a member of the group. Other clans, denied the mysterious knowledge of animal behaviour and superior tool-making ability that give his clan such an advantage on the hunt, either move away or are disbanded in raids organized by the clever ones. The women are taken by the raiders and are incorporated into the clan structure, but the men are usually killed or chased away. Soon there are too many clan members to live in one small territory, and in the ensuing arguments over access to food some of the young men take their mates and set off to find new territory. The process is repeated many, many times over the next few thousand years, until essentially every man in the region traces his ancestry to that first, clever child.

What I have just described is a process that could have occurred around 60–70,000 years ago in Africa, as a single fortuitous event changed the course of human evolution. As with many historical events, it depended on the right person being in the right place at the right time – a coincidental triptych that provided the spark for a revolution. But is this necessarily the way things happened?

The short answer is that we simply don’t know. The anthropological term ‘Great Leap Forward’, coined by Jared Diamond, was borrowed from Mao Tse-tung’s 1950s plan for the industrialization of China to describe the development of radical shifts in technology at the onset of the Upper Palaeolithic, around 50–70,000 years ago. These ‘killer applications’, as we called them in the last chapter, marked a radical departure from the way of life that had gone before, and they deserve an explanation. What caused human behaviour to change so significantly?

Richard Klein, one of the strongest supporters of the Great Leap Forward theory, cites three significant archaeological shifts that occurred around this time. First, the tools used by humans became far more diverse and made more efficient use of stone and other materials. Second, art makes its first appearance, with a presumed leap in conceptual thought. And finally, it is around this time that humans began to exploit food resources in a far more efficient way. All-in-all, the evidence points to a major change in human behaviour. And Klein points to our DNA as the reason.

The sorts of changes we see at the onset of the Upper Palaeolithic could only have come about, he argues, if we began to communicate with each other more effectively. He infers from this that the onset of the Upper Palaeolithic marks the origin of modern language, with its rich syntax and multitude of ways to express oneself. This flowering of language skills is thought by most anthropologists to be a critical prerequisite for further social development. The development of complex social networks is almost certainly the spark that brought about the changes in Upper Palaeolithic behaviour. And this, Klein believes, happened because of a change in the way our brains are wired, set in motion by a genetic event.

We can gain some insight into what these changes may have been by looking at modern children. Swiss psychologist Jean Piaget, working in the mid-twentieth century, developed a detailed scheme for normal child development. It involved a progression from object recognition to a gradually more complex understanding of the way in which objects relate to each other. Most of the earliest stages focus on organization of real-world objects (such as bottle, rattle, or Daddy’s face) into ever more complex systems through the adaptation of behaviours (when I
see Daddy’s face, I usually get a bottle, or sometimes a rattle). It sounds complicated, but it does seem to explain the trial-and-error way in which children learn to interact with their world. It also provides a framework for the acquisition of language skills, the most uniquely human behaviour.

Children begin to speak by ‘babbling’ – random sounds that roll off the tongue. This babbling phase gives way at around twelve months to actual words. Many psychologists and linguists think that children’s first words, such as ‘mama’ and ‘papa’, are the easiest to learn, genetically programmed into human vocal anatomy in some way. They are found almost universally in all languages, suggesting that there may be a grain of truth in this. The American linguist Merritt Ruhlen, however, argues that the universality of these words is the evolutionary remnant of a common origin for all human languages – a trace of the original language spoken tens of thousands of years ago – rather than a programmed anatomical by-product. It is likely that both attributes play a role, with the most basic sounds having been used in the first human language
because
they are the most basic sound combinations produced by our vocal machinery.

The babbling and single words continue for another year, with a massive expansion of the child’s vocabulary. The first two-word sentences begin to emerge during this process, as the child combines different words to form a clause with a new meaning. My older daughter’s name is Margot, and during this phase she began to say things such as ‘Margot kiss’ and ‘Mummy hold’. Then, around age two, a massive leap in spoken language occurs. It is at this age that most children begin to put together three words into complex sentences – ‘Margot kiss Daddy’, rather than simply ‘Margot kiss’ or ‘Kiss Daddy’ – with the subject-verb-object (SVO) structure, or syntax, that characterizes English and most other human languages. The structure SOV (‘Margot Daddy kiss’) is used by a few languages (Japanese, Korean and Tibetan among others), while VSO and VOS structures are used by around 15 per cent of languages (Welsh is an example of the former and Malagasy of the latter). The rarest structure of all is OSV, perhaps best known from the film
The Empire Strikes Back
as the language of Yoda the Jedi master: ‘Sick have I become’ and so on, used by only a handful of languages spoken in the Brazilian Amazon.
The important thing to glean from this syntactic diversity is that word order plays a crucial role in our understanding of a sentence. As the old saw goes, ‘dog bites man’ is mundane trivia, while ‘man bites dog’ is newsworthy.

So, the explosion of linguistic complexity in a two-year-old is a result of the mastery of syntax, and from then on it is a never-ending barrage of ever more complex sentences. The great leap forward in understanding, however, involves crossing the syntax barrier-without a mastery of this, the rest will never happen. This is what we see with chimpanzees taught to use American Sign Language, such as Kanzi the bonobo. Kanzi was able to create and understand a wide variety of two-word sentences, like an eighteen-month-old human infant, but he never mastered the complex syntax of a two-year-old’s speech. The significant difference in human vs. ape communication seems to have been the creation of brain structures that allowed an understanding of syntax, and thus the communication of complex meaning.

To see why this might be, let’s try another thought experiment. Imagine that you are cast away on a remote island into a tribe of people speaking a language unintelligible to you. Nothing in the language makes sense – there are no cognates with anything in your mother tongue. Your goal is to find out where you are and how to return home. How would you do it? Initially, it is likely that you would try to communicate using the skills that you developed as a young child – trial and error, focusing on nouns and verbs in isolation. Pointing to a tree, you raise your eyebrows questioningly, relying on the near universality of many human facial expressions (themselves perhaps an evolutionary remnant of a time before complex speech developed). Soon you learn enough words to develop basic sentences – ‘I drink’, or ‘Eat now’. The final leap will be to create complex sentences that convey much more information than single nouns and verbs alone. You congratulate yourself on the achievement of two-year-old speech when you can finally say ‘I go home now’. At this point, the locals seem to have a ‘eureka moment’, whereupon they take you to the other side of the island, to the local airstrip where you can catch a flight home.

This imaginary shipwreck scenario serves to demonstrate the utility of syntax for human communication, and gives us a good idea of why
it might have been such an enormous leap forward for our early human ancestors. What it fails to do, though, is to explain what may have caused it to happen. If the intellectual chasm between humans and apes is spanned by a syntactic bridge, we need to ask why it appeared in our ancestors but not those of chimps and gorillas. Here again we obtain some help from primate behavioural research. One of the things that prevents chimps from developing complex syntax, according to Sue Savage-Rumbaugh, is limited short-term memory. To understand the meaning of a complex sentence, you must remember the beginning when you reach the end in order to integrate them. Not difficult, perhaps, for ‘man bites dog’, but a little tougher for a complex past-tense construction in German, where the active verb in the sentence only shows up at the end! Limited short-term memory may be the root cause of chimpanzees’ minimal language skills.