by Guy Murchie
If people all over the earth always married at random, choosing their mates by lot regardless of what country, race, class or religion they came from, it would take something like 35 to 40 generations for all their family trees thus to merge completely in common ancestors, the time beyond 30 generations needed because of the aforementioned slowdown in backward ancestral multiplication, a rate which progressively decreases from two to one and ultimately even below one when the family trees begin to encompass all humankind, whose numbers of course were smaller in earlier centuries. But obviously people do not mate at random, for there have always been barriers to boys and girls getting together: oceans, high mountains and vast distances between them; rigid marriage laws, religious sex taboos and innumerable racial and cultural prejudices. On the other hand there have been almost as many compensating influences tending to overcome these barriers and increase the scope of mating: long hunting trips for vital food, nomadic herding, expeditions for business or war with its spoils in slaves and women; also strict laws against incest and inbreeding, all naturally abetted by man's primordial appetite for novel amorous adventure.
Probably most significant of these factors, geneticists agree, are the nearly universal rules of endogamy (inbreeding) and exogamy (outbreeding) that respectively permit marrying persons to pick each other only from inside the membership of a specified larger, endogamous social group (such as a tribe or caste) yet also only from outside a specified smaller exogamous group (like a clan). In many sophisticated countries today of course the endogamous group is nothing less than mankind and the exogamous group is one's own immediate family, which gives a man latitude to propose to practically any uncommitted female in the wide spectrum between his niece and a chimpanzee. But virtually all the more primitive of human societies have traditions that greatly restrict marriage. In rural tropical Africa, for example, the average tribesman is expected to marry inside his tribe of perhaps ten thousand people yet outside his family clan of one or two thousand, giving him a total population of some eight thousand to pick from.
In a few rare cases tribal members have been even more restricted endogamically, as in the inbred clan called Foldi in the Hyabites tribe of Arabia, all of whose people have six toes on each foot and five fingers plus thumb on each hand and who have come to value their 24 digits so highly they will kill any 20-digit baby born to them as the illegitimate issue of an adulterous mother. The same goes for the monkey-tailed clan of Kali who traditionally refuses to keep any infant who doesn't have a tail.
Laws of exogamy, on the other hand, can be at least as extreme in the opposite (outward) direction and the marriage law in much of western Europe during the time of the Crusades defined incest as extending out to fifth cousins. In some other parts of the world the outbreeding groups were even larger, as in imperial China, where one was forbidden to wed anyone with the same family name, a rule that diverted the average Chinese bridegroom away from about a million of his closer relatives and undoubtedly contributed much to the homogeneity of that most populous nation.
Weighing the marriage customs of Earth, then, as annotated in reports from Westermarck's classic History of Human Marriage to the latest sexological research, it appears that the rules of endogamy have generally been enforced less rigorously than the rules of exogamy. This is presumably because the natural suspicion a few people may feel toward someone else's exotic consort from an alien land is less apt to arouse public disapproval than the natural revulsion those same people feel toward a liaison that can be called incestuous. Also if a man in ancient or medieval times married his sister, he would forgo his opportunity for aid in the form of brothers-in-law to hunt or fight with or ultimately to avenge his death. And so these various regulations of outbreeding and inbreeding have probably not, in net effect, greatly inhibited man's genetic circulation within his species. In sum, it would seem a reasonable estimate that, while geographical factors in historic times must have held back the gene flow between a man and mankind by perhaps ten generations, other factors have more or less canceled out to keep human kinship confined to about the fiftieth cousinhood range.
It is practically impossible to set limits on where any man's family connections may reach upon the habitable earth. And the very proliferation and complexity of his relations is incomprehensible to most of us for, even if you assume only two children to a couple, as I have done in the accompanying simplified diagram (a quota actually too low to permit humanity to survive), everyone on the average must have first cousins (the children of his uncles and aunts), 16 second cousins (the grandchildren of his great-uncles and great-aunts), probably 64 third cousins, about 250 fourth cousins, roughly 1000 fifth cousins and some million relatives as close as tenth cousin. Then, if you extrapolate on into the billions, which means extending your relatives to all humanity, it is evident that, even after allowing liberally for the shared ancestry of spouses and all the barriers to intertribal and intercontinental marriages, the range of fiftieth cousins will still easily cover the planet. This is not to claim that there has been more than a trickle of intercontinental travel in bygone millenniums in which Celts, Phoenicians, Vikings and Polynesians are now known to have sailed to America, and Papuans, Melanesians, Malays and Negritos to have trafficked in Australia - but, in the nature of things, a trickle is all it really takes to establish close cousinhoods. It is scarcely possible, I admit, for the most perspicacious of minds to visualize cause and effect reliably over thousands of years and tens of thousands of miles. One could as reasonably expect a mayfly who lives a day to understand the love life of a turtle who lives a century, But it is demonstrable nonetheless that a single indirect genetic contact between Africa and Asia in a thousand years can make every African closer than fiftieth cousin to every Chinese. Surprisingly, this may happen without any natives of either continent doing any particular traveling at all, but simply in consequence of the wanderings of nomads in intermediate territory. No single nomad would have to travel more than two or three hundred miles in his lifetime either, a meager enough total for a carefree tent-dwelling herdsman. Yet inevitably every generation produces at least a few would-be Marco Polos, mettlesome young bloods who keep going for thousands of miles, zestfully overcoming every hazard, swimming rivers, running borders, fighting brigands, making off with girls as they find them - and obviously it needs only a couple of brothers of this stamp to make first cousins of their own children on opposite sides of the earth - first cousins who, like as not, do not even know of each other's existence. If you can accept this fact, that an African family in the Sudan, for example, can be first cousins of a Chinese family in Hangchow without any Africans leaving Africa or any Chinese leaving China, then it shouldn't be too much for you to understand that there must be thousands of relationships at least as close as fifth cousin at comparable distances and that the tremendous genetic circumfusion of fiftieth cousinhood cannot help but take in the bulk of mankind.
To see how such interrelationships work, look at the illustration (next page), in which an old nomad living in Persia has eight sons who, one after the other, set off to seek their fortunes, each in a different direction. The son who goes to China predictably marries a Chinese girl and has half-Chinese children who are first cousins of the halfblack offspring of the son who went to Africa and married a black girl on the upper Nile, all of this new generation of course being grandchildren of the old nomad of Persia. Later the African son's descendants naturally increase in number with succeeding generations until they include practically everyone in his tribe along about the thirteenth generation (even assuming only two children per family), by when his genes must inevitably have spread (through raids, wars, migrations and resulting infractions of endogamic law) to various other tribes, whose members in turn all become descendants of the old nomad by about the twenty-fifth generation. And after that his spreading waves of progeny must irregularly continue to advance tribe by tribe all over Africa and beyond, relentlessly filling up each endogamous pocket until by the fift
ieth generation it can hardly help but include everyone.
"How do you know," I hear you ask, "that there were actually enough raids, wars and migrations in the past twelve hundred and fifty years to carry the old nomad's genes from tribe to tribe at the rate you claim?"
"How do you know," I reply, "that flowers in the garden will be cross-fertilized by the bees as the bees collect their food?" The two questions are analogous, both having to do with probability in genetic combinations on a broad statistical scale. And they are close to the well-known mathematical laws of rolling dice and the roulette tables of Las Vegas. For as the number of bees multiplied by their feeding rate and divided by the number of flowers tells you how often the average flower will be pollinated, so, by more complex equations, you can estimate the minimal cognate circulation of man, which, it turns out, affirms the extreme unlikelihood of any viable segment of human population being able to avoid all outside contact for anything like a thousand years.
Of course a few snobbish people will protest, "But my family is an exception. We traced our ancestry back eleven hundred years and they all came from an isolated community on the Isle of Man where they spoke Manx and never had any marriage contact with the outside world."
Statements of that sort cannot possibly stand up to close scrutiny. Genealogists, I admit, will often trace a prominent family name back for hundreds of years - which involves only the relatively simple procedure of following one male line of descent. But the average person has approximately a million ancestors with some thousand names just in the last 500 years and it is patently impossible to trace any large portion of them. Even such a well-publicized lineage as the Mayflower descendants from Plymouth, Massachusetts, can hardly begin to track down their relatives of 350 years, and a little knowledge of early Yankee seamanship and fecundity in the tea and slave ports of Asia and Africa, plus mathematics, will show that their ranks probably now include more than a million Chinese in China, a comparable number of Hindus in India and blacks in Africa - not to mention several million Americans and Europeans.
Even if at some period there really was an isolated, highly inbred clan on the Isle of Man, could anyone possibly prove it had maintained complete sexual segregation for even a hundred years? Any boy who escaped to the mainland or adventurer who arrived from anywhere might have established a relationship between it and the rest of the world. Is it not likely that some such incidents took place in every generation? To be sure, the traditionally proud family archives may show one or two honorable descent lines of reputed purity, but they have a way of neglecting to include the black sheep and their illicit or unorthodox doings, if indeed such ever got beyond being just suspected in the first place.
There is probably more than enough interracial gene flow right inside your own country to make you a close cousin of practically anybody imaginable. Dr. N. C. Botha, the immunologist who worked with Dr. Christiaan Barnard's heart transplant team in South Africa, calculated that the "white" people of Dutch extraction there have an average of 7 percent "nonwhite" genes, while the two million so-called colored people have 34 percent "white" genes. And the Ohio Journal of Science has estimated that 155,000 "Negroes" passed over the color line to become "whites" in the United States during the decade 1941-1950, indicating the dimensions of the accelerating flow of genes between the black minority and the white majority that is largely fueled by the waxing tide of black-white espousals now known to exceed one percent of all American marriages.
WHAT IS A RACE?
It should hardly be necessary now for me to point out that there is no such thing as a pure race, nor any race of men on Earth that is unrelated to other races. Fact is: if such a race existed, it would be a species. But races are not species: they are (by definition) only subspecies. And all the peoples and races now existing on Earth are demonstrably of one single species, that being the largest group classification of organisms that regularly interbreed and reproduce their kind. This biological fact actually tells a lot about the homogeneity of the genes of Homo (man) whose species name is Homo sapiens, rather immodestly bestowed on him by Linnaeus in the eighteenth century. In a sense it is also science's own measure of the brotherhood of man.
It may be instructive here to contrast man with the mule, who enjoys no comparable brotherhood because he is not a species. The reason there is no species of mules is that the mule is not an interbreeding organism, for, with rare exceptions, a mule is sterile and cannot have little mules. So if you want to raise a mule, you must find a jackass and breed him to a mare (as has been well known at least since the days of Aristotle), the mule being a donkey-horse hybrid, an explicit kind of cross between two species. Normal humans of course do not have the mule's sterility, mankind being a species, so any mulatto or cross-breed between any two (or more) races of man may marry and have normal children. That is one of the important proofs of close human kinship, demonstrating that intermarriage between races must have always been going on, and obviously it has never stopped long enough to make interbreeding sterile in its results. Strong evidence for such a persistent prehistoric interracial mixing of genes comes also from numerous archeological excavations of the remains of divergent races in the same areas, such as bones from Aurignacian (white), Grimaldi (black) and Solutrean (yellow) peoples all evidently living as neighbors in southern France about 25,000 years ago.
Man's propensity to diversify into races, please note, seems to be characteristic of all the earth's most successful species because, say evolutionists, it gives species additional ways of adapting to environmental challenges such as an ice age, a warm age or a wet age (when all continents sink into the oceans) and, even in the most stable of times, it lets them live in more extensive and much more varied territories than any one single race possibly could. An example is the fact that polar bears and European brown bears interbreed and produce fertile cubs, showing they are races of a single species. Another is the recent discovery that herring gulls have diversified their species into 13 races living in various regions of the northern hemisphere, two of which share the same territory of northwestern Europe although they are unable to interbreed directly with each other. These two races, however, are known to interbreed with fellow races in adjoining areas so presumably their genes are constantly commingling through the indirect route of the half dozen other herring gull races ringing the Arctic Ocean. Of course races occasionally get separated by seas or mutations or fateful quirks of courtship, whence over the millenniums they diverge so far they evolve from subspecies into species. By such means presumably the hundreds of thousands of species of insects, reptiles, birds and mammals arose on all the continents of Earth. But man, outdoing the most pliant of his competitors (perhaps the rat, cat or housefly), became so adaptable he learned to move freely over vast distances (even more so than the birds) and to live in any country in any season, hot, cold, thin-aired, arid or wet, while still avidly intermarrying back and forth among all his races, remaining thereby, for better or worse, a single species.
A mental hurdle to acceptance of man's close kinship may come from the resemblance usually noticeable among brothers and sisters, a family similarity which may understandably (if illogically) give one the notion that any two persons who do not look alike (say an Arab and a Swede) cannot be related. This common error is due to failure to realize that diversity persists in the most inbred of families, often between twins, in every race without exception and in humanity as a whole, which today obviously receives no "new blood" from chimpanzees, gorillas, orangutans or other of its nearer outside relatives. I do not, mind you, discount the statement of geneticist Geoffrey H. Bourne of the Yerkes Primate Center that there is "very little physiological reason" why man-ape hybridization via artificial insemination might not succeed - something that predictably will become the subject of an actual experiment one of these days.
But, regardless of any such development, diversity is a profound attribute of life and basic to Darwin's theory of evolution through natural selection am
ong the ever-new, ever-different variations in all life forms, a diversity inexorably bestowed upon the species man by complex but fairly regular mixtures that produce gradients between all the so-called black, white and yellow races on Earth, as suggested in the accompanying illustration. And no amount of cross-breeding will eliminate it for, as Theodosius Dobzhansky categorically states, "if all peoples on earth were to intermarry at random, the resulting humanity would not, as is frequently but mistakenly supposed, be some kind of a compromise between all the now existing races. It would rather be an extremely variable lot: some persons resembling each of the now existing races would continue to be born, but other individuals would have combinations of traits that are rare or non-existent at present." His genetic explanation is that "pure' races could exist
only if heredity were like a fluid transmitted through 'blood,' and if the hereditary 'bloods' of the parents would mix and fuse in their offspring." But, as you will recall (page 161), Gregor Mendel discovered last century that the old "blood" theory of heredity is plainly wrong. And in this century the microscope of the modern biologist has clinched it by proving that red blood cells have neither a nucleus nor any kind of heredity, can therefore be safely transfused from person to person, and that blood actually has less to do with heredity than any other part of the body.
To use the classic analogy, heredity is like a hand dealt from a huge deck of cards. Each child in effect (page 164) is dealt half the combined parental deck. If your parents together possess a total of 20,000 genes, which may well be true, the hand dealt you by heredity would contain 10,000 genes. Each of your brothers and sisters must also receive 10,000. Except in the case of identical twins (who originate from the same sperm-egg union), each brother or sister receives a different combination of 10,000 genes. Almost all your own genes may be duplicates of the 10,000 received by one of your brothers or sisters, or almost all 10,000 may be different. Any combination may chance to happen, but the number of genes is so large that, under the aforementioned law of probability, it is considered virtually impossible that the same exact combination of genes could happen twice in all the past or future existence of humanity.