Recursion, which is a crucial aspect of human thinking and communication, certainly would have arisen early on in human cognition. This is the ability to think thoughts about thoughts, such as, ‘Mary is thinking that I am thinking that the baby is going to cry,’ or, ‘Bill is going to get upset when he finds out that John believes that his wife is being unfaithful to him.’ Recursion is also seen in the ability to break tasks down into other tasks, such as, ‘First build the spring. Then place the small spring inside a lock. Then place the lock inside another lock and a spring within the larger lock.’ And it is visible in complex syntax in sentences: ‘John said that Bill said that Peter said that Mary said that Irving said …’ It is not clear whether any non-human species is able to use recursive thought, nor whether erectus or neanderthalensis spoke recursively. But it would not have been necessary for them to have recursion to have language, at least according to the simple idea of language evolution as a sign progression and supported by some modern languages.
It is not difficult to imagine a scenario in which complex or recursive thinking might arise. Suppose that someone is born with the ability to think recursively. This ability to think (not necessarily speak) recursively would provide a cognitive advantage over other members of their community, enabling them to think more strategically, more quickly and more effectively. They might become better hunters, better defenders of the community, or makers of complex tools. This indeed could help them to survive and would in all probability make them more attractive than the competition to the opposite sex, leading to more mating and more offspring. It could also lead to children with the ability to think recursively. And soon this ability would spread throughout the population. At that point only would it be possible to speak recursively and therefore for this new property to be incorporated into the grammar of the community. In other words, there could never be a gene for recursive syntax, because what is needed is a gene for recursive thinking across cognitive tasks. Recursion is a property of thought, not language per se.
Thinking through the implications of these various sources of change in a species, it becomes clear that a single mutation in a particular behaviour such as language would be unable to guarantee that all humans possess the same genetics that they had at the time the original change was introduced. The genotype could have been altered by the Baldwin effect, by genetic drift, or by a population bottleneck.
Still, there is another force in evolutionary theory that can exercise a role in the spread and modification of languages over time. This is ‘population genetics’.
Population genetics is concerned with the distribution and frequency of alleles within an entire population. How do groups adapt to their environment? How are new species formed? How are populations divided or structured? Population genetics is one of the most challenging areas of evolutionary theory because of the mathematical sophistication it requires for its application – controlling many variables in many individuals and many links between variables and individuals simultaneously.
One of the pioneers in this field was a postdoctoral associate of Morgan, Theodosius Dobzhansky. Dobzhansky built a bridge between micro- and macroevolution. Basing his studies of populations in their natural habitats, Dobzhansky showed that these populations, however similar they were phenotypically, manifested large degrees of genetic diversity below the surface. Though this genetic diversity is unseen, Dobzhansky demonstrated that is it is always there and is crucial as particular subpopulations differ in their genetic make-up. This diversity renders each subpopulation subject to distinct phenotypic adaptations and speciation, given the right pressures and constraints on gene flow (frequency of mating between the subpopulations).
Dobzhansky was but one of many researchers who examined cross-breeding and genetic drift in small populations and how these could push populations away from one ‘adaptive peak’ – a kind of local equilibrium in which the environment and the organism match well for a period of time. The basic ideas of population genetics turn out to be crucial to the understanding of change in individual languages and groups of languages over time.††
An overview of the various subfields of genetics and evolutionary change leads to the recognition that fossils are not the only pieces to the puzzle of human origins. The resources of molecular biology are also needed for a full picture. As the genomes of a variety of primates are sequenced, we can begin to estimate dates at which the different lineages of primates diverged evolutionarily. Therefore, because we know that humans and chimpanzees share 96 per cent or so of their DNA sequences, closer than any other two primates, it then follows that there was a common ancestor of humans and chimps unshared by other great apes. Further work leads to the conclusion that this common ancestor split off from other great apes about 7 million years ago. Humans are thus one of the newer apes. From this lineage it is clear that all humans originated, as Darwin predicted, from Africa.
So we know quite a bit about early humans and the story of how life came to be on our planet. But how do we know this? More than DNA evidence is necessary. The reconstruction of the evolution of our species requires the sweat of hard fieldwork, finding, studying and classifying fossils. Here evolutionary theory takes on characteristics of an adventure novel. Who were these fossil hunters? What did they do for our understanding of human evolution? And how did competition and cooperation among them advance the science behind the evolution of human language?
* I deviate slightly from Peirce here. For Peirce, indexes were more complex than icons, as used and elaborated by humans. But as used by non-humans and in evolution, I believe that indexes precede icons.
† This chart provides more detail than we will refer to elsewhere in this book. It should be seen as implicit in the primate chart of Figure 3.
‡ There are other hypotheses on the origins of life. One that is widely supported, though by no means universally accepted, is the so-called ‘RNA world hypothesis’. According to this hypothesis, since the essence of life is self-replication and since RNA has this property, the presence of RNA would have preceded both proteins and DNA. DNA would have come later to provide storage or memory capacity to the RNA and proteins would have eventually been synthesised, taking over some of RNA’s functions, though of course RNA continues to be essential to life as we know it.
§ Histones are the packaging around DNA that controls how genes are activated and deactivated.
¶ Genera is the plural of genus, which is a set of species sharing an immediate common ancestor.
# Unfortunately Darwin’s ideas about how traits are ‘passed along’ differ greatly from what we now know to be true about genetics, which is hardly surprising given that he died before modern genetics had been developed.
** We now know something that Mendel did not, namely that individual alleles are selected by the process of meiosis, in which a haploid cell (a cell with only half of the normal number of chromosomes for a particular species) is formed. Two haploid cells (ovum and sperm) are contributed, one by each of the two parents, before reproduction begins.
†† In addition to Dobzhansky’s work, that of many others was also important. This work led to what came to be known as the ‘new synthesis’ in biology and among its leading researchers were Ronald Fisher, especially in his 1930 book, The Genetic Theory of Natural Selection, and Sewall Wright, as in his 1932 concept of ‘adaptive landscape’.
2
The Fossil Hunters
What we do see depends mainly on what we look for … In the same field the farmer will notice the crop, the geologists the fossils, botanists the flowers, artists the coloring, sportsmen the cover for the game. Though we may all look at the same things, it does not all follow that we should see them.
John Lubbock
THOUGH DARWIN INITIALLY SEEMED WRONG in his Africa-first hypothesis, the first evidence that he might be right came from a German geologist, Hans Reck, shortly before the First World War. Not only was Reck the first European to behold the Olduvai Gorge in
Africa’s Great Rift Valley, his team was the first to recognise a hominin fossil there.
As confirmation of Darwin’s theory and for palaeontology more generally, the Great Rift Valley is vital and famous in the study of human evolution because of the fossil riches preserved by its unusual geological properties. The term originally described a 3,700-mile trench running from Lebanon to Mozambique, a fascinating geological formation that emerged from the splitting of the earth’s crust. However, most researchers today understand ‘Great Rift Valley’ to refer to something smaller, to the part of East Africa where new tectonic plates are forming and literally beginning to tear the African continent apart. To find such a place anywhere on earth is to find a time-machine. Descending through the geological layers in the Rift Valley is like travelling back through history to prehistory, a journey of several million years. Even though the interpretations of finds in the valley are often complicated by mixing and corruption of fossil sites by tectonic upheaval, flooding, volcanic activity and so on, the Great Rift Valley has been and continues to be of inestimable importance for evolutionary theory.
When he was there in 1913 to study the earth’s geological history and to excavate fossils, the twenty-seven-year-old Reck recognised this. And his work paid off. Near the end of three months of hard work, in the formidable East African equatorial heat, a crouching skeleton was discovered in one of the oldest layers of the gorge. Reck recognised that the remains he had discovered were of a Pleistocene Homo sapiens who probably had drowned there some 150,000 years ago.
The year was an ominous one, of course. Soon the ‘War to End All Wars’ began and palaeoanthropological research was suspended in order to carry out the sinister work of mass killing. For that reason, not much else was to come from Olduvai until the arrival of Louis Leakey more than twenty years later.
Leakey was a controversial researcher who energised palaeoanthropology in much the same way that Chomsky did linguistics and Einstein physics (though Leakey did not lead as a theoretician). He shook up his field by grandiose claims that attracted publicity both to the field and to Leakey himself. Along the way he and his family discovered some very important fossils in East Africa. Louis also fostered research on primates in their natural habitat, recruiting and encouraging researchers such as Jane Goodall (chimpanzees), Dian Fossey (gorillas) and Birutė Galdikas (orang-utans) to undertake their own field research.
After both advancing the earlier research of Hans Reck and eventually working alongside Reck himself, Leakey and his team discovered artefacts such as Olduwan and Acheulean tools, a skull of Paranthropus boisei, then called Zinjanthropus, and Homo habilis, among many others. Leakey and the headline-making publicity he received attracted many scientists to palaeoanthropology. Whatever his shortcomings, he earned his place as one of the innovators and founders of the field of palaeoanthropology.
More importantly, the findings of Leakey and other palaeoanthropologists have provided incredible insights into the evolution of our species. We now know that the human skeleton evolved over the last 7 million years or so, from the first likely hominins. Some of the features that distinguish us from other species include bipedalism, encephalisation, reduction of sexual dimorphism, hidden oestrus, greater vision and reduced sense of smell, smaller gut, loss of body hair, evolution of sweat glands, parabolic U-shaped dental arcade, development of a chin, styloid process (a slender piece of bone just behind the ear) and a descended larynx. These traits have become important to the classification and understanding of the place of different fossils in the hominin line.
One of the adaptations of human skeleta to the world around them came as evolution provided a novel form of locomotion. Humans are the only primates that walk upright. Other primates favour crawling or tree-swinging to get about. But to walk habitually (unlike a chimp, an orang-utan, or a bear that can walk upright only occasionally and for brief periods), our skeleta needed to change from the basic primate model to support this upright posture. One example of its many changes is found in the hole at the bottom of our skulls, called the foramen magnum. This is the aperture through which our spines connect with our brains. When this is found at the back of the underside of the cranium, we know that the creature did not walk upright regularly, because it would have been extremely uncomfortable. The spine would emerge nearly parallel to the ground for a creature on all fours, but awkwardly incline the head if the creature walked upright.
Another important milestone, the human head and brain, was achieved by a long process of encephalisation, the gradual process by which our brain cases got larger. Hominin brain case volume increased from about 450cm3 for australopithecines to sapiens’ 1,250cm3. The heads of hominins show larger and larger brain cases until the appearance at Homo sapiens (neanderthalensis had even bigger brains than sapiens, averaging about 1,400cm3 for males). Sapien skulls are large, rounded and delicate compared to the smaller brain cases and thicker skulls of our hominin ancestors. Gone are the special ridges at the top of hominin skulls to anchor muscles for chewing, along with the heavy brow ridges that perhaps shaded our eyes from the sun. In their place came a larger brain. And our heads developed accordingly, to give room and horsepower for thinking.1
Male and female bodies also grew more similar in size – that is, our sexual dimorphism was reduced. Although human males are roughly 15 per cent larger than human females on average, this size difference is smaller than that of any other primate species. The reduction of sexual dimorphism in the primate line has social implications. When males and females become more similar in size, this correlates, among primates, with pair-bonding, or monogamy. Male primates spend more time helping females feed and raise children. This is particularly important for human primates, since our children require a longer time to mature.
In some Western, industrialised cultures as much as one-third of a person’s overall life expectancy is ‘childhood’ – the length of time required to reach autonomous adulthood. If males and females bond for life or simply in order to raise children, then the male will no longer need to battle other males for mating access. This reduces the pressure for males to have larger physical size, longer canines and other features for fighting. Battle is no longer necessary in order to pass our genes along to the next generation.
Along with bipedalism and reduced sexual dimorphism came a greater reliance on vision. Humans can see further than other primates, and most other creatures, which enables them to run faster towards a visible goal. Moreover, beginning with the arrival of Homo erectus humans acquired the capability of ‘persistence hunting’, running down game until it tires and the hunter kills it with a stone axe or club, or until it dies of exhaustion and overheating. Persistence hunting is seen even today in societies such as the Gê communities (Mebengokre, Kĩsedje, Xerente, Xokleng and others) in the savannah regions of the Brazilian Xingu river basin.*
Evolution is also the ultimate economiser. With humans’ greater dependence on vision came a loss of acuity and range in their sense of smell. If one portion of the brain gets bigger or better, another part very often grows smaller in the course of evolution. Here, the ability to smell degenerated as the vision region of human brains grew. Today the portion of the brain available to vision is roughly 20 per cent. (Fortunately, if someone is born blind, the vision region can be enlisted for other functions – evolution is often an efficient, no-waste process.)
Other changes to human physiology, not all with an immediately obvious intellectual benefit, might also have enhanced our species’ intelligence. In the course of evolution, the length of the gut of hominins shrank. Intestines and digestive processes required fewer and fewer overall calories, enabling Homo bodies to shift more of their energy resources to their growing, ever-hungry brain with its expanding cranium. But natural selection does not receive all the credit for this change. Cultural innovation also played a role.2 Homo erectus learned to control fire as long as one million years ago. As pre-erectus hominins learned to eat cooked food, the fats and pro
teins that they then ingested were much easier for their digestive system to break down. Whereas until this time, hominins, like other primates, needed larger guts in order to break down the large amounts of cellulose in their diet, as hominins learned to cook they were able to eat more meat and consequently able to consume more energy-rich food and to reduce significantly their dependence on uncooked plants that were much harder to digest. This fire-enabled dietary change facilitated natural selection’s ability to produce larger brains in hominins, because their digestive organs required less energy and less space in the human body, while at the same making it possible to consume far more calories far more quickly (assuming the availability of meat). Cooking also altered our faces. It rendered the massive jaw muscles of pre-Homo hominins redundant and made our faces less prognathous. This in turn reduced the burden on the cranium to offer supporting structures, such as the mid-sagittal crest of the australopithecines, that arguably impeded the growth of the human brain case.
There are critics of this change-through-fire hypothesis. They hypothesise that Homo erectus was a scavenger and a hunter, finding rich sources of meat from carrion and fresh kills of its own long before controlled fire. Whatever the reasons, this reduction in gut size represents the movement to modern human anatomy. When encountered in the fossil record it is therefore a clue that the species represented by the particular fossil could be further along the evolutionary line to Homo sapiens.
Other important physiological changes needed for us to become modern humans included our upright posture and its by-products. As humans stood erect and walked habitually upright, their bodies became more efficient at thermal regulation. Moreover, since an upright body’s surface areas are less exposed to direct sunlight than a quadruped’s, hair became less necessary for humans. As a side benefit of shedding body hair, it became easier for humans to cool their bodies. They also evolved sweat glands in conjunction with the hair loss, making thermal regulation much more efficient. In hot, dry climates, the absence of hair and the production of perspiration allowed humans to cool off more quickly than many other animals. And sexual selection may have further sped up hair loss if people preferred less hirsute mates. This was all important to sustaining the human metabolic rate, so crucial for our intensely calorie-consuming brains.
How Language Began Page 5
