The most ubiquitous mammalian resource of the future: the human body.

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EIGHT

THE FUTURE
EVOLUTION OF
HUMANS

What about the future evolution of our species? How will the future world and its new environments affect our own evolutionary outcome � or will we be affected at all? Will we become larger or smaller, or gain or lose intelligence, be it intellectual or emotional? Might we become more, or less, tolerant of oncoming environmental problems, such as a dearth of fresh water, an abundance of ultraviolet radiation, and a rise in global temperature? Will we produce a new species, or are we now evolutionary sterile? Might the future evolution of humanity lie not within our genes, but in the augmentation of our brains through neural connections with inorganic machines? Are we but the builders of the next dominant intelligence on Earth � the machines?
Fossils tell us that evolutionary change is not a continuous thing; rather, it occurs in fits and starts, and it is certainly not �progressive� or directional. Organisms get smaller as well as larger, simpler as well as more complex. And while most

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lineages evolve through time in some manner, the most dramatic evolutionary changes often take place when a new species first appears. If this is the case, then future morphological evolution in Homo sapiens may be minimal. On the other hand, we may show radical change in our behavior and perhaps our physiology. Perhaps � and this is the biggest perhaps � a new species of human will evolve in the not so distant (or distant) future. But such an evolutionary change would almost surely require some sort of geographic isolation of a population of humans, and as long as humans are restricted to the surface of the Earth, such an event seems unlikely.
Since the time of Darwin, it has been accepted that the forces that produce new species are usually brought to bear when small populations of an already existing species get separated from the larger population and can no longer interbreed with it. Gene flow, the interchange of genetic material that maintains the integrity and identity of any species, thus gets cut off. Of course, genetic isolation generally means geographic separation, which means new environmental conditions, different from those experienced before. When you add this into the mix, you have a recipe for making a new species � given enough time, and continued isolation.
New species have formed many times in the course of human evolution. Although there are many gaps in the record (and disagreements among the specialists, with much work left to do), we can sketch a rough outline of human evolution. The human family, called the Hominidae, seems to begin about 4 million years ago with the appearance of a small proto-human called Australopithecus afarensis. Since then, our family has had as many as nine species, although there is ongoing debate about this number. About 3 million years ago two new species, A. africanus and A. aethiopithecus, appeared, while another, A. boisei, first appeared about 2.5 million years ago. (These three species are sometimes identified as Paranthropus instead of Australopithecus.) But the most important descendant of A. afarensis is the first member of our genus, Homo, a species named Homo habilis (�handy man�) for its use of tools, an ability that is about 2.5 million years old. This creature gave rise to Homo erectus about 1.5 million years ago, and H. erectus gave rise to our species, Homo sapiens, either directly about 200,000 to 100,000 years ago, or through an evolutionary intermediate known as Homo heidelburgensis. Our species has been further subdivided into a number of separate varieties, one of which is the so-called Neanderthal. (Some researchers consider the Neanderthals to be a separate species, Homo neanderthalis, but this is still highly disputed.)

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Each formation of a new human species occurred when a small group of hominids somehow became separated from a larger population for many generations. Then, following rapid morphological transformations, Homo sapiens, once evolved, showed little or no further evolutionary change.
Although major structural changes in H. sapiens may now be over, many smaller evolutionary changes will undoubtedly take place. Prominent among these might be a homogenization of the current human races. The same forces resulting in the homogenization of the Earth�s biota are at work on us: our former geographic isolation has been broached by the ease of transportation and the dismantling of social barriers that once kept the very minor genetic differences of the various human racial groups intact. The most obvious change that may come about would occur in skin color. Because rapid transportation and global communication have destroyed most barriers to human movement and even isolationist human culture, we move about more. As we do so, we tend to interbreed, and thus the barriers that once selected for various types of skin pigment are no longer present. Skin pigment is one of the most heritable of human genetic features, and it may be that humanity is heading for a universal brown-skinned future, as the darkest of the black-skinned races get lighter and the melanin-free skins become darker. The humanity of ten thousand years from now might be but a single shade of color, a pleasing chocolate brown.
In stature, each race of our species seems to be getting larger, yet this is surely not a genetic feature: with improved nutrition we are simply maximizing the height potentials carried by our genes.
But in many ways, natural selection as we know it may not operate on our species at all. It is being thwarted on many fronts by our technology, our medicines, and our rapidly changing behavior and moral values. Babies no longer die in large numbers in most parts of the globe, and babies with the gravest types of genetic damage, which were once certainly fatal in pre-reproductive stages, are now kept alive. Predators, too, no longer affect the rules of survival. Tools, clothes, technology, medicine: all have increased our fitness for survival, but at the same time have thwarted the very mechanisms that brought about our creation through natural selection.
As an example of new human speciation, let�s look for a moment at what it would take to create a new species with a much larger brain � say, a brain size of about 2,000 cubic centimeters, compared with the average value of about 1,100 to

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1,500 cubic centimeters in Homo sapiens. What conditions of natural selection on Earth today would engender such a change, and would such a new creature even belong to our species?

Intelligence and the Bell Curve

If Homo sapiens sapiens (the modern form of our species) were grouped together with an australopithecine, a Homo habilis, a Homo erectus, and an archaic Homo sapiens, what would the significant intellectual differences be? Would the other species use language, sing songs and create music, dream of flying, or even draw pictures? Before tackling these questions, we must first ask ourselves, what is intelligence?
There are several definitions of intelligence: what you use when you don�t know what to do; guessing well about what fits together; finding an appropriate level of organization; finding an appropriate pattern from the available information. Although these statements certainly typify aspects of brain function that we recognize as intelligence, such definitions remain highly unsatisfactory. It is clear that intelligence is composed of an enormous array of components. Some of us have great math skills; most do not. Franklin D. Roosevelt, the longest-serving American president and certainly one of our best leaders, was an indifferent student. (Oliver Wendell Holmes once remarked of him, �A second-class intellect, but a first-class temperament!�) His English contemporary and Second World War stablemate, Winston Churchill, was so indifferent a student that he never completed college and was packed off to the military by his despairing parents. Yet both rose to lead great countries in crisis through their political skills � clearly reflecting keen intelligence. Surely an ability to master politics is as much a type of intelligence as the ability to solve partial differential equations � but it is just as surely a very different type of intelligence. As any practitioner of �intelligence testing� can readily assert, the commonly used tests, such as the long-reigning IQ tests, measure some small portion of a great system of brain organization and function loosely termed �intelligence�.
In the end, the definition of intelligence is probably irrelevant. For in spite of periodic hand-wringing by those who argue that our species is doomed to an ever-decreasing average intelligence because less intelligent people are having more children, there is very little chance of IQ (or any other measure of average intelligence)

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changing any time soon. The reason for this is that intelligence, by almost any definition, is produced by hundreds or even thousands of individual genes, and is thus very difficult to change. It is estimated that the correlation between an individual parent�s intelligence and that of his or her child is 0.2%. Since both parents contribute, this effect is multiplied: thus the correlation between the parents� intelligence and that of their offspring is 0.04%. What this means is that two parents with IQs of 140 will probably conceive a child with an IQ of 100 � as will two parents with IQs of 80.
Nevertheless, we remain fascinated by the concept of quantified intelligence, its history in our species, and the possibility of its long-term heritability. Those interested in the evolution of our species have probed the minutest anatomical differences among our various fossil predecessors in an effort to determine how and when our lineage began to �get smart�. Yet this information is maddening in its incompleteness, and applying a present-day understanding of learning to the study of early humans is impossible. It has long been clear, for example, that the brain of a newborn human and the same brain only two to three short years later are vastly different, and the by-products of those differences are the marvelous characters of humanity. The toddler can speak in sentences, reason, remember, and move about independently; the infant can do none of these things. During the developmental period, and for years afterward, neurons are connecting and changing their morphology in ways still largely unknown to science. And no information about such changes is available to the paleoanthropologist when it comes to early humans. The most we can know of the brain of Homo erectus is its size and a bit about its shape, gleaned from the interiors of fossilized skulls. The real bits of information behind intelligence � the morphology of human brain cells and the pattern of their connections � is the area where the great secrets lie.
Two persons who have met with some success in this area are Terry Deacon of Boston University and William Calvin at the University of Washington. Deacon is a neuroanatomist who has studied the various attributes making up human intelligence. He has concluded that the emergence of human intelligence came about not through some mysterious new neurological or morphological invention within the brains of the earliest modern human species, but through the development of already-present circuits and cells. In other words, our species used �off-the-shelf equipment� that was then wired in novel ways through the processes of evolution.

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Calvin, a neurobiologist, has put forward similar arguments about how intelligence came about through evolution. Calvin sees intelligence as the evolution of structural thought processes, such as syntax, the nested embedding of ideas; agendas, the ability to make novel plans for the future; logical chains of argument; and the ability to play games with arbitrary rules. And, last of all, Calvin sees a beautiful leap in the evolution of human intelligence: at some point, humans, alone among the animal world, began to perform and eventually write music. Calvin has presented a most interesting hypothesis about how all of this came about: he thinks that intelligence may be a by-product of a brain that evolved to throw better. So many new �connections� and novel pathways were necessary to create the neuroanatomy required for throwing weapons at prey that unforeseen consequences resulted from this newly evolved brain. In particular, it became intelligent.

Unnatural Selection

In his book Children of the Ice Age, paleontologist Steven Stanley has made the observation that the advent of medicine has disrupted natural selection as it acts on humans. Humans, according to Stanley, have created unnatural selection, for our species now routinely heals or saves many individuals who would never survive in the �wild�. Furthermore, not only do we save individuals with physical or mental defects, we also allow them to breed. Now, with the increasing power of genetic engineering, we are poised to take unnatural selection to new levels, not only for a host of nonhuman species, but for ourselves as well.
One of the most provocative assertions about how our species is evolving at the present time comes from Dr. David Comings, a physician and geneticist specializing in human genetic disorders. In 1996 Comings published The Gene Bomb, a book as controversial (if far more overlooked) as The Bell Curve. Comings spent two decades studying Tourette�s syndrome and attention deficit hyperactivity disorder (ADHD) among children, and came to the startling conclusion that the incidence of such genetically inherited disorders is increasing in the human population faster than population growth alone should dictate. His conclusion is that our species is evolving ever greater numbers of behavioral disorders.
Comings first came to this realization when treating his patients diagnosed with Tourette�s syndrome and ADHD: he noticed that the frequencies of these disorders were high in the children of his patients. Instead of these behaviors being the

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result of an increasingly complex society, he surmised that society was selecting for the genes that caused these behaviors � a case of unnatural selection.
Further work now suggests than many of humanity�s so-called �behavioral disorders� � such as ADHD, depression, addiction, and impulsive, compulsive, oppositional, and cognitive disorders � have a significant genetic component, and unlike intelligence, may be coded on only a few genes. If this hypothesis is correct (and no authoritative study has yet been able to falsify it), it means that the heritability (the rate at which such a trait is passed on to the next generation) of such disorders is very high. If selection acts to favor the transmittal of highly heritable traits, they very quickly increase in the overall gene pool of a species. Comings has summarized this stark view as follows:

Of course, these inherited behavioral traits are certainly affected by the individual�s environment: many people carry the genes making them susceptible to addictive disease, but under many or even most circumstances do not succumb to alcoholism or drug addiction. Yet many others do. Comings took his findings even further, and postulates that many victims of ADHD reproduce at an earlier age than those without the syndrome, since very few of these sufferers attend college, and many women carriers become pregnant at an earlier age than women either attending college or entering skilled positions. The result is that women attending college, and then entering careers, ultimately have fewer children. These women are usually of higher intelligence than the population mean, and have lower frequencies of behavioral disorders. Women bearing children earlier � and having more children as a consequence � will be passing on their genes with more efficiency. While this difference will have little or no effect on intelligence, Comings believes that it may be highly significant in increasing levels of behavioral problems in the population.

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Comings�s theory is controversial for two reasons: the data and their interpretation. First, the increasing frequency of reported cases of depression, ADHD, and the like may simply be due to an increased awareness that these disorders can be treated, which encourages people to report them with greater frequency than they did in the past. Second, even if these disorders are indeed on the rise, they may have only a small genetic component, and may be due to any number of environmental causes, including increasing levels of environmental pollutants such as lead and other heavy metals, as well as organic macromolecules, in drinking water. Given these two issues, it is hard to say whether there is merit to Comings�s assertions � but they provide an interesting example of the potential for further evolution in our species, involving genes that we usually do not think of as being capable of evolution.

Human Behavior and Directed Evolution

We tend to think of evolution as something involving structural modification, yet it can and does affect things invisible to the morphologist � such as behavior. In fact, it may be that much of humanity�s future evolution will involve new sets of behaviors, allowing us to deal with the changing set of environmental conditions facing our species: life in cities, life among crowds, life in a world where certain behaviors affect survival.
Because we have directed the evolution of so many animal and plant species, we might ask ourselves, why not direct our own? Why wait for natural selection to do the job when we can do it faster and in ways beneficial to ourselves? This is precisely the tack taken by many behavioral geneticists who are searching for ways to manipulate human genes. Behavioral genetics is a new branch of science that asks what in our genes makes us different from one another (vs. what makes us different from other species or what makes us human). Scientists working in this field are trying to track down the genetic components of behavior � not just of problems and disorders, such as those profiled in the previous section, but of everyday behaviors that may well be heritable traits: overall disposition, the predilection for addiction or criminality, many aspects of sexuality, aggressiveness, and competitiveness. These are traits that we know intuitively to be at least partially heritable.
The implications for the future of our species are incalculable. It seems unlikely that our society will not eventually accede to the idea that DNA samples should be given to genetic specialists. When this happens, elaborate screenings of an indi-

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vidual�s genetic makeup will become commonplace, and specific genes for depression and other behavioral abnormalities will be detected. The second step will be the application of behavioral drugs using newly discovered chemical pathways. But the third step will be actual changes in people�s genes. This can be done in two ways: somatically, by changing the genes in a relevant organ only; or by changing the entire genome � what is known as germ line therapy. Since germ line therapy involves changes in the genetic code of a person�s eggs or sperm, it will not help the individual in question, but it will help his or her children.
The major obstacle to the genetic engineering of humans is a property known as pleiotropy: most genes perform more than one function, and many functions are coded on far more than one gene. All genes involved in behavior are probably pleiotropic. This is surely the case, for example, with the many genes involved in human intelligence (in fact, neuroanatomists and behavioral geneticists believe that the genes involved in IQ are probably involved in many basic brain functions as well). Therefore, far more will have to be known about the human genome before wholesale tinkering can begin, since very slight changes in gene frequency could lead to drastic changes in the species-level genome. As has often been quoted, a mere 1% difference in the genome is all that produces the vast gulf between chimpanzees and humans.
Why change genes at all, then? In all probability, the pressure will come from parents wanting to �improve� their children: to guarantee that their child will be a boy (or a girl), tall, beautiful, intelligent, musically gifted, sweet-natured, or wise, or to ensure that their children won�t become addicts, thieves, mean-spirited, depressed, or hyperactive. The motives are there, and they are very strong. The Human Genome Project, now completed, had for much of its motivation (whatever it supporters argue) the desire to find �bad� genes. Once they are found, new Herculean efforts will be required to weed them out. Assuming that it does become practical to change the nature of our genes, how will that affect the future evolution of humanity? Probably a great deal, if the practice continues over millennia.
If natural selection is unlikely to produce a new human species � the event foreseen by H. G. Wells in his novel The Time Machine � the same end result could certainly be achieved by directed human effort. As easily as we breed new varieties of domesticated animals, we have it in our power to bring a new human race, variety, or species into this world. Whether we choose to follow such a path is for our descendants to decide.

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Just as the push by parents to enhance their children genetically will be societally irresistible, the assault on human aging will be a force of unnatural selection in the future. Much recent research shows that aging is not so much a simple wearing down of body parts as it is a system of programmed decay, much of it genetically controlled. It is highly probable that the next century of genetic research will unlock numerous genes controlling many aspects of aging, and that these genes will be manipulated. An individual human lasting between one and two centuries is an obtainable goal. Whether or not it should be pursued, in light of human population growth, is another question.
Here is a scenario already posited by several scientists (and science fiction writers) that could potentially lead to a new human species, or at least a new variety. Some parents allow their unborn children to be genetically altered to enhance their intelligence, looks, and longevity. Let�s assume that these children are as smart as they are long-lived � they have IQs of 150, and a maximum age of 150 as well. Unlike us, these new humans can breed for eighty years or more. Thus they have more children � and because they are both smart and live a long time, they accumulate wealth in ways different from us. Very quickly there will be pressure on these new humans to breed with others of their kind. Just as quickly, they will become behavioral outcasts. With some sort of presumably self-imposed geographic or social segregation, genetic drift might occur and, given enough time, might allow the differentiation of these forms into a new human species.

Dyson among the Machines

Humans are no longer simply tool makers. Now we are machine makers as well, and not all of the machines we make can be considered tools. In ways perhaps even less predictable than our use of genetic manipulation, it may be our manipulation of machines � or they of us � that creates the most profound evolutionary change in our species. Not simple morphological change, or even behavioral change (although that might happen too) � but a change as consequential as the first enveloping of one bacterium by another to produce the symbiotic by-product now known as the eukaryotic cell � the key to animal life. Is the ultimate evolution of our species one of symbiosis with machines? Numerous writers have discussed the prospect, but in the late twentieth century, at least, perhaps none so evocatively as George Dyson, particularly in his book Darwin among the Machines: The Evolution of Global Intelligence.

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The subtitle of Dyson�s book sums up a possible trend in the future of our species. But according to Dyson, that global intelligence will not be a product of Darwinian evolution among the fusing populations of Homo sapiens, but will come about through an ongoing symbiosis with the machines we build: �Everything that human beings are doing to make it easier to operate computer networks is at the same time, but for different reasons, making it easier for computer networks to operate human beings�.
In science fiction books and movies, this kind of symbiosis is portrayed as a machine and a man linked by cables � the contact of wire and neuron as a shared pathway of electrons. Would such a linkage enhance intelligence, if it were possible at all? Neuroanatomists claim that such linkages are only a matter of time and money, and that the first benefit of such a linkage will be enhanced memory � the ability for an individual to immediately access the knowledge of the collective. But is memory � and data � intelligence? Dyson points out that H. G. Wells pondered this subject in his lifetime, concluding that some sort of global intelligence was the only hope of improving the affairs of humanity. Wells prophesied that the whole human memory would soon be accessible to every individual. In Dyson�s view, �Wells acknowledged memory not as an accessory to intelligence, but as the substance from which intelligence is formed�.
All of us who routinely use computers have suffered from some lack of memory in our systems, be it RAM or space on a hard disk drive, and such nuisances invariably detract from some other task, break our concentration, require an unanticipated change in activity. It is easy to see how extra memory space � or extra memories � would change the world and the way we perceive it. But would it increase intelligence? Most thinkers who ponder this subject assure us that it would, though in ways that may not be perceptible to us, perhaps because an enlarged, networked intelligence would operate at time scales different from ours, and thus invisible to us. As Dyson notes, it might also operate in a fashion unlike that of Darwinian evolution:

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In an earlier chapter, we asked whether the �rules� of speciation have changed for humans. The answer is that they have not � humanity may have affected the nature of the playing field and the players, but we cannot change the rules. Yet in the merging of man and machine that conclusion may be overturned. The evolution of machines and machine intelligence does have directionality, toward ever greater complexity and intelligence. Machine intelligence does not go backward as much as it goes forward; there are no functional equivalents of a blind cave fish or the whale, a mammal that returned to the sea. In the computer world, direction is progress: better operating systems, more machine interconnections, more memory, easier use, more humans connected.
Dyson further argues that information comes in two types: structure and sequence. The first is the map of space, the second the map of time. Memory and recall are translations between these two types of bits. Thus it is Dyson�s fervent belief that the future evolution of humanity lies in �technology, hailed as the means of bringing nature under the control of our intelligence, thus enabling nature to exercise intelligence over us. We have mapped, tamed, and dismembered the physical wilderness of our Earth. But, at the same time, we have created a digital wilderness whose evolution may embody a collective wisdom greater than our own�.
As breathtaking as Dyson�s vision is, I differ slightly in predicting the type of machines we may merge with. One of the tired old saws in the science fiction pantheon is the notion of a silicon-based life form. There is a simple but powerful retort to that possibility. The variety of �organic�, or carbon-based, compounds found in life processes can be readily seen by going to any chemical supply store and checking out the store�s catalogs. They are book-sized. Silicon-based compounds, on the other hand, fill only a good-sized comic book. Silicon, however useful it may be for the electronics and computer industries, is none too suitable for life. We may soon find that it is none too suitable for the computers of the future, either, or for the machines we may try to merge with.
Perhaps, after all, the progression of Earth�s dominant animals will be Age of Bacteria, Age of Protists, Age of Invertebrates, Age of Fishes, Age of Amphibians, Age of Reptiles, Age of Mammals, Age of Humanity � and then a long Age of Artificial Intelligence. This certainly seems to be the view of many of the moguls and thinkers spawned in Silicon Valley. Of these many prophets, none seems so bullish concerning the coming replacement of humanity by thinking machines as Ray Kurzweil. His vision is starkly writ in The Age of Spiritual Machines. Kurzweil believes that the

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invention and routine construction of computers that have the computing power of the human mind will occur early in the twenty-first century, and that machines that outstrip the capabilities of the human brain in some attributes of processing and logic will inexorably appear soon after. In his view, the merging of human and machine (or at least artificially constructed) brains will be inevitable. But will it ever be heritable?

Growing Buildings and Changing Trophic Levels

Science fiction is so pervasive and voluminous in its output that there are few ideas not already in use in some futuristic plot device. Thus, the two ideas I throw out here are surely well known to its aficionados. However, they seem to me to be two potentially realistic strategies that could alleviate both our population problems and the stresses our metals-based industries place on the rest of the world.
Many of our industrial problems and pollutants come from the processing of metals. The industrial smelting and forging of tools and technology made from iron, aluminum, nickel, tin, copper, and the many minor metals and their blended components requires massive supplies of energy and water and produces volumes of pollution. Although it would require significant genetic manipulation to create organic structures and tools, humanity might be better off by �growing� as much technology as possible. On a very small level, researchers have already experimented with this idea: a square tomato has been developed to suit packaging needs. More imaginatively, a living house made of growing wood and other organic structures might be a way to realize sustainability in a technical society.
Yet an even more dramatic breakthrough could be realized by manipulating not only our machines and technology, but also ourselves. Humans require massive amounts of food. We, like all animals, are heterotrophs � we must ingest other once living matter in order to live. The world could support far more people if we could somehow radically re-engineer our food and nutrient needs so as to become autotrophs � organisms at a lower trophic level. Plants and many types of chemoautotrophic bacteria use sunlight or chemical energy to power their metabolism. If biotechnology could help get humanity off its hamburger diet (or even its wheat diet) and merge with the plant world, a great deal of stress on the planet could be alleviated. Solar-powered calculators do remarkably well; perhaps the only hope for an Earth even remotely resembling its past self in terms of habitats and diversity is solar-powered humans.

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New Human Species?

Our lineage has produced new species in the past. What about the future?
Speciation requires an isolating mechanism of some sort. The most common is geographic isolation, whereby a small population gets cut off from the larger gene pool, then transforms its own set of genes sufficiently that it can no longer successfully reproduce with the parent population. Most species have done this through geographic isolation, yet the very population size and efficiency of transport of humanity make this possibility remote � at least on Earth. If, however, human colonies are set up on distant worlds, and then cut off from common gene flow, new human species could indeed arise.
Perhaps humans will lose (or voluntarily discard) the technology that allows the global interchange of our species from continent to continent. If separation lasts long enough, and if conditions on the separated continents are sufficiently different, it is conceivable that a new human species could arise due to geographic isolation.

Scenarios

Let us conclude with some alternative scenarios of humanity in the future. Once we leave aside our guilty assumption that our species will soon go extinct somehow, we are left with what Rod Taylor (in the film version of H. G. Wells�s The Time Machine) described as �all the time in the world�. With hundreds of thousands to millions of years yet to play with, what might our species evolve into? Here are four scenarios:

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Evolution takes time. Humanity probably has that � as much as a billion years of it � as I will show in the next two chapters.

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CONTENTS