"Where is the evolution of humankind heading?" Where will it take us? This question is uppermost on the mind of Vassily Velkov, a degree-holding biologist and staff researcher at the RAS Institute of Biochemistry and Physiology of Microorganisms in Pushchino-on-the-Oka. To begin with, he makes this reminder: that the chief mechanisms of biological evolution are in spontaneous genetic variability and natural selection. Now, the spontaneous genetic variability occurs as a result of mutations (gene transformations) and recombinations (rearrangement or genes of their parts) as genetic information is passed from generation to generation. Everything is at the mercy of chance here. That is why organisms even within one and the same population are always somewhat unlike both genetically and, consequently, physiologically. Those more adapted to their medium and environment survive and multiply, while those less adapted disappear little by little. That's the substance of natural selection.
Which means that biological evolution has no predetermined goal. It proceeds just "where the wind blows" so that organisms could survive and, at best, proliferate as much as possible. Biological evolution would have never come to be had there been no genetic diversity, and changes in the environment: in a stable medium stabilizing selection eliminates extreme ("out-of-the-way") variants and sustains the norm, the "middle way".
It's a different matter as far as the evolution of the human population goes. The higher human society is advanced economically, the weaker natural selection in it. Natural selection is actually absent in industrialized countries, what with a high standard of health care and nutrition. Therefore carriers of mutations harmful to viability do not die out but pass down their genes to progeny. These accumulate in a population to make its biological survival ever more dependent on better health protection and living standards, dependent on scientific and technological progress.
Alongside natural selection that decides blindly who is to live and who is to die, there is yet another evolutionary mechanism, the sexual selection. It rules who should produce offspring in the first place. Unlike the natural selection that removes too "bad" genes, this mechanism keeps down the number of individuals with "weak" genes and gives the green light to the strongest. In some highly organized communities of the animal kingdom, among primates for example, it is the chiefs who pass down their genes to offspring. According to the now commonly adopted view, at the level of sexual selection evolution deals not only with "physiological" and morphological characters, it also deals with behavioral characters too.
Now what determines behavior. The long practice of selection over thousands of years shows that many of the behavioral responses are determined by genes, and thus the latter are subject to selection. Scientists researching in behavioral genetics conduct targeted cross-breeding experiments on dogs, mice, rats, quails and other animals so as to increase their cognitive abilities, change their emotiveness (resistance or, conversely, liability to fear), enhance or reduce their aggressiveness-all that through artificial selection. At each particular stage of these experiments one crossed animals with some extreme characteristics to obtain, in ten to twenty generations, a new line with manifestly expressed characters.
A comparatively new trend in behavioral genetics, the genetics of personality, goes into the effect of genes and of the environment on three principal groups of people's behavioral responses: cognitive abilities, psychological character traits and psychopathology. Now we know for certain that genes are mainly responsible for a good many of the psychological and intellectual characteristics of man like, for instance,
such essential qualities as activity and passivity, hypochondria and anxiety, a sense of independence and dependence, altruism and egotism, intelligence, aggressiveness, sexuality. This is not to mean that there is a gene showing "preference for organ music" or "for vacationing on Mount Everest". Not at all. Such characteristics are largely predetermined by the interaction of many genes forming an integral personality type in which particular character features are not mutually contradictory, as a rule.
At the present stage of genomic studies we can say that inheriting a certain behavioral character is a statistical characteristic of the whole population, not of one human individual. Yet further research into particular genes responsible for intellectual and behavioral characteristics might make it possible to assess their effect in concrete individuals.
As Dr. Velkov says figuratively, genes are a filmed image, while their medium (environment) is like a developer whose effect depends on its quality and conditions. By modifying the latter two factors, we can improve the image or make it worse, but we cannot obliterate it.
True, the quantitative evaluation of cognitive abilities, IQ tests in particular, and other methods are questioned as to their reliability. This is the target of many disputes. But the very principle of such kind of approach has been widely recognized-the problem is now to improve the methods of quest and of the statistical processing of results.
Twins are one favorite object in studying the factors responsible for an individual's cognitive and behavioral characteristics. There are twins and twins: monozygotic (uniovular) and dizygotic (dioval) twins. Uniovular twins, since they come from one and the same fertilized egg cell, are genetically identical, while dioval twins-coming from two different egg cells-are only half identical. Say, for some reason twins happened to be separated and reared in different families and in different conditions. Well, uniovular twins remained intellectually and psychologically alike in every respect, no matter whether they grew up together or apart. Moreover, in psychological and cognitive characteristics they were like their biological, not foster, parents.
Now, cognitive abilities are an essential characteristic that makes man different from animals and that underlies memory and learning. The genetic impact varies in specific individuals, especially in adults. It has been proved in the course of many studies: IQ values are determined by a set of genes, over 100 in number.
Most of the intelligence genes are concentrated within the sex X-chromosome-such evidence was obtained long ago. In males IQ values are found within a much wider range than in females and encompass both low and high intelligence areas.
Genes leading to psychic disorders are inherited by children from their mothers, not fathers, even though the mothers may not show any symptoms. But psychic diseases occur 30 percent as frequent among men as among women.
The cause of all these differences is as follows: the female genome contains two identical sex chromosomes (XX), while the male genome-two different ones: X (female chromosome), and Y-that of the male sex proper. The X-chromosomes are diploid (having a double set) with respect to all other chromosomes, while the diploidy of Y-chromosomes excludes sex chromosomes. This means that the genetic information encoded by X-chromosomes is duplicated in females, but not in males. Yet both in males and in females only one X-chromosome is in action, for the other is inactivated in the early stages of embryonal growth. Which of the two in particular- this is a matter of chance. Therefore should any mutations (useful or harmful, it doesn't matter) occur in one of the two female sex chromosomes, the probability of their manifestation will be 50 percent. Since males have but one X-chromosome, such probability will be equal to 100 percent. Although in women one of their sex chromosomes is inactive, it is passed on to their children and can become active in them.
The material evidence obtained lately shows that many mutations resulting in psychic diseases are localized in X-chromosomes. Furthermore, mutating genes that cause mental disorders are 2.35 times as numerous in these sex chromosomes as in all the other, nonsex chromosomes. And here's something else as well. Men have much better chances (by several orders!) than women in getting "high intelligence" genes, and they come into play much oftener, for men have only one X-chromosome. Therefore men have a broad spectrum of IQ, up to the extreme values. It looks as if Mother Nature has duplicated all genes save those responsible for intelligence in males. But it is in them that mutations are realized quickly, which might be the reason for the accelerated development of intelligence in Homo sapiens.
In X-chromosomes, side by side with intelligence genes, are genes regulating the reproductive functions. As shown recently, malfunctions in the intelligence genes tell on the performance of the intelligence genes. Indeed, among people having low IQ (below 70) more than 30 percent leave no progeny; those with IQ in a 101 to 110 range have 10 percent childless; but among those with IQ above 131 only 3 or 4 percent beget no offspring. The evolutionary role of this setup of sex X-chromosomes is obvious.
Intelligence is intimately related to language. A gene whose mutations lead to speech disorders has been identified in the chromosome 7q31- it has been isolated, cloned and analyzed, and dubbed FOXP2. Its mutation results in poor enunciation and in worse language and grammar aptitudes.
To study the evolution of FOXP2, its informational structure was compared with analogs in mice, rhesus macaque, orangutan, gorilla and chimpanzee. The present form of this gene is found to have originated about 200,000 years ago, which agrees with the paleontological evidence on the time of the appearance of humans with contemporary anatomical characteristics. Human populations spread fast all over the planet owing to effective speech aptitudes due to useful mutations in FOXP2. This view has thus been confirmed.
But how are the many "intelligence and psychology" genes implicated in the present evolution of man? According to Dr. Velkov, here what is called assortative mating has a role to play, that is when couples sharing some common character will mate. That is to say, individuals with a definite set of genetic (and, consequently, behavioral and physiological) characters choose like marriage partners.
Here's one common delusion: spouses are thought to be psychologically alike because they have adjusted to each other. It has been proved that mutual adjustment has nothing to do with that, the cause lies in assortative mating. At the behavioral level such kind of congeniality ensures steady interindividual relations, it minimizes conflict situations.
But what kind of "like" genes do attract one another? First, the intellectual level, a basic genetic character, is an important part of assortative mating. As shown by many statistical studies, IQ values among longtime marriage mates are quite close, especially in the region of high and low magnitudes.
It's odd enough, but alcoholism is also a part of assortative mating. Daughters born to alcoholics (father or mother, no matter), though free of this malady, marry alcoholics twice as often as those whose parents do not indulge in drink. As to the sons born to dipsomaniacs, they will show no preference for Bacchantes as wives.
The high assortativeness of intermarriages among schizophrenics and other mental cases was described long ago. It carries an important evolutionary meaning: in generations to come mental diseases are more pronounced and occur at a younger age. Ultimately a gravely ill person will not marry at all and will leave no progeny. So the pathogenic genes are withdrawn from a population's gene pool in the end.
Assortative mating, though expressed moderately, is statistically significant among people prone to depression, affective psychoses, panic and sundry phobias. All this goes to show that assortative mating as a free, though not always conscious, choice among individuals has genetic, evolutionary implications.
Velkov V.V., "Where Is the Evolution of Humankind Heading?", Chelovek (Man) Journal, No. 2, 2003
Prepared by Igor GORYUNOV
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