Who are our Ancestors? [From The Nation 20.520 (17 June 1875): 405-407.] ⁴³

THE principles of heredity established by modern inductions in biology tell against the barbaric traditions of law and heraldry and for the rights of women, so far, at least, as the influences of strictly inherited qualities, both mental and physical, go towards determining our natures—namely, for the equal right of women to be counted among our ancestors. The likelihood in the average of a grandson’s resembling his maternal grandfather in any quality is as great as that of resembling the paternal one; and a granddaughter is as likely to resemble in any quality her paternal grandmother as the maternal one. This law, which appears rather by the failure of the various fanciful hypotheses held on the subject of heredity than by positive

evidence sought for it, is on this very account the better founded in accordance with the canons of induction—namely, by the method of difference, or the absence of exceptions, taken together with the positive evidence for heredity generally. But this law does not imply that there is any tendency of one sex to transmit to the other any proper qualities of its own, except in that latent state which the law essentially implies, and which, as a mode of transmission, is one of the most important inductions in biological science, having various illustrations and applications.

Nearly all laws of heredity are properly laws of averages, against which, of course, evidences may be massed by a partial or one-sided induction. They can in general be held to be true only as governing averages; or at best as being laws of such real tendencies as mask and modify and even countervail one another. Such real tendencies have been made out by the more philosophical observers, like Dr. Lucas, through the judicious choice of subjects for investigation least likely to be affected by chance or training— e.g., rarely-occurring physiological peculiarities. Some special laws have thus been made out, such as the tendency of transmission to the same sex of individual characters or peculiarities first appearing in one, though otherwise they have no special relation to sex; and on the other hand, the more general secular, slowly-acting, and weaker tendency of transmission to both sexes of qualities, or degrees of qualities, which originally belong to one. This tendency is shown only in connection with the tendency to inherit acquired qualities at earlier and earlier ages, or periods of life, and therefore in a manner independent of adult sex development. The causes which keep the sexes different are, however, much more powerful than this tendency, which is apparently operative only where qualities so transmitted have ceased to be of special sexual importance, or have lost, as they readily might in this case, their original association with sex.

Individual prepotency, again, or the preponderance of influence upon offspring of one parent over the other; the absence of perfect equality of influence in all respects, or the accidental inequality of influence, which may be said to be the most invariable fact of heredity, masks and confuses all other laws, whether of averages or of real tendencies. But this prepotency does not appear to belong to one sex more than to the other; so that the rule holds that in the long run the two sexes are of equal influence in transmitting individual or family characteristics, so far as these are independent of the influences of education and family traditions; and it should be especially noted that characteristics associated with sex are transmitted latently, though none the less really, through the sex in which they do not appear. The very large part, however, which education has to play in human development—in the election and fostering of hereditary tendencies—is another masking and confusing cause, which may account in great measure for traditional and popular notions about descent, but does not really interfere with certain general conclusions in answer to the question, Who and how many are our real ancestors, or those who have determined our really inborn natures? We are quite ready to agree with those who cry, “Great is education!” This power is, indeed, the scientific foundation of law and moral responsibility; but heredity is also great, and even adds to, we believe, instead of diminishing, the true grounds of social institutions, the rights of law and punishment.

The importance of heredity leads to the rather startling consequence from the equality of the sexes in determining descent (exhibiting the role which sexual generation takes in the phenomena of organic life generally), that all living beings, both animals and plants, of races in which sexual generation is the prevailing mode of reproduction, derive their natures on the average from every productive individual of only a few generations back whose descendants have survived within their race or biological province. The true genealogical tree of science branches backwards—a cause of great difficulty and annoyance to the genealogist. When we take account of strictly inherited natures and variations of natures, setting aside the conventions of names and the traditions of external inheritance, we are led by the rule of the equal transmission of inborn qualities by both sexes to search for our origin through two parents and four grandparents, to eight great-grandparents (or six if one’s parents are first-cousins), and sixteen potential great-great-grandparents. And our “gret-gran’thers multiplied by three” would, with their equal spouses, make thirty-two. We call these “potential” ancestors of the fifth degree, since, on account of the intermarriages of relatives within permitted grades of consanguinity, even the sixteen possible ancestors of the fourth degree may be condensed, so to speak, to the lesser number even of eight. Such reticulation or interlacing of branches in the back-reaching lines of ancestry through which one may arrive by several paths to the same individual ancestor (who, therefore, fills the place of several potential ancestors), becomes more and more frequent, and ultimately, or in the long run, a predominant feature of the natural genealogical tree; for it takes but twenty generations or about live hundred years to reach a generation with more than a million potential ancestors in it, or one which can bo reached through more than a million various lines of ancestry. We call two lines different, even though they may coincide in all but small portions of their courses.

It is in a high degree probable in the average case that a few thousand individuals have filled the larger number of these million places, since true races, even of men, are usually confined to narrow provinces. An insular position like that of Iceland is not the only kind of isolation in a race which would make any one of the present generation a descendant by so many thousands of lines (on the average) from every productive individual of twenty generations ago, as almost certainly to make every such individual, who has any living descendants at all, an ancestor of all now living in the province of his race. The agricultural peoples of the counties of England appear to be thus isolated in great measure, so that of a few thousands, five hundred years ago, each would be an ancestor of almost all living at the present time in his county. But neither such provincial limitations of a race, nor any but the most rigid caste interdictions of marriage, would prevent an English lord’s being the descendant of a very large number of peasants of five hundred years ago, since the interdicted marriages are not between absolutely separated castes, and alliances descend by small grades in the social scale, without scandal, through collateral lines, in the course of a few generations, from the noble to the serf; and ascend by the same grades.

The case of Iceland affords an instructive illustration of the remarkable effect of the biological principle of bi-sexual generation, namely, that in a comparatively short, almost insignificant, period in the duration of a race, even the most advanced has the solidarity of a zoophyte. Iceland has been occupied for about thirty-eight generations by a nearly fixed population of fifty thousand—an isolated race of Scandinavians. The number of potential ancestors which any one has of the thirty-eighth degree is about two hundred and seventy-five thousand millions. All these were represented in the case of the present Icelanders by fifty thousand emigrants; so that on the average each emigrant filled the places of five and a half millions potential ancestors, or could be reached on the average by this number of partially differing reticulate lines of descent. If we reckon the average duration of human life at a third of a century, the condensation on the whole has been from five hundred and fifty thousand million possible ancestors of all degrees, to the thirty-eighth inclusive, down to the one million four hundred thousand who have actually lived in the island, or to one in three hundred and ninety-three thousand of potential ancestors. It is thus made almost certain that every original emigrant to this island who has any present descendants at all is an ancestor of all now living. A doubt of this conclusion arises, however, from the circumstance that the inhabitants have been more or less divided into isolated provinces; but if occasional intermarriages between members of different provinces have amounted to one in ten thousand marriages, a connection through these of every present inhabitant with all the original settlers would be in a very high degree probable.

Common qualities in the Icelander distinguishing him from others of the Scandinavian races, such as travellers have noticed, and especially physiological ones like that early noted by Sir Henry Holland (of a superior stature in the Icelandic men, due mainly to the greater lengths of their spinal column) would not necessarily require the supposition of a close intermixture of the race to account for it, unless it be an instance of that morphological variation to which limited races are more subject than extensive ones. But such a physiological character is more likely to be the direct common consequence of similar conditions, exercises, and modes of life, and of their inherited effects, than of the mere drifting of morphological variation on one hand, or the survival of characters from the advantages of them in the struggle for existence. The human struggle usually depends, or has come to depend, on other than merely bodily or athletic grounds of advantage. Intelligence and strength in union or brotherhood have long been the vantage-grounds of the human contest in the competition of race with race, or tribe with tribe, and in opposition to unfavorable external conditions. And biology affords a proof, in the natural genealogical tree, of the merely natural brotherhood of men quite as impressive as the theological derivation of the race from a single pair; but does not make so complete and emphatic a reference back to one concentrated responsibility for human weaknesses and sins. How great this becomes on the theological theory can also be estimated by the above mathematical reasoning. Thus, if the degree of relationship of any ancestor to a descendant be represented by the number of places of potential ancestors of his degree occupied by him, compared to the whole number of that degree, then the relationship of each parent to their offspring would

be one-half; that of each grandparent one-quarter; of each great-grandparent one-eighth; except from the marriage of first-cousins, which would make a pair of the eight fill two-eighths each, or one-quarter, or be of the same degree as grandparents: and if in any remote generation a single pair could have filled all the places of the potential ancestors of that generation, their relationship to all their descendants would be of the same degree as that of immediate parents; so that though the number of potential ancestors of the generation of the estimated time of Adam would be a number requiring more than seventy numeral figures to express it, yet with all these concentrated, as was possible, in a single pair, this pair comes to have the proximity of relationship to us of immediate parents. Such ancestors as Adam and Eve would therefore be nearer relatives to us than our grandparents.

A recent newspaper correspondence has discussed the statement that the Roman Princess Torlonia, though of a family which became prominent only eight centuries ago, was yet the descendant of a thousand Colonnas. The thirty-two generations which may be assumed for this period would give the princess about eighty-six hundred millions of potential ancestors in all. This number, which would of course in any case be greatly reduced by the intermarriage of remote relatives, might easily include among its representatives many thousands of persons bearing this family name, but would doubtless also be represented by many more thousands of persons as humble in name and origin as the Colonnas were eight centuries ago.