Calotype

“ Descent of Qualities in a Population.—Let us now endeavour to obtain a correct understanding of the way in which the varying qualities of each generation are derived from those of its predecessor. How many, for example, of the V class in the offspring come respectively from the V, U, T, S and other classes of parentage? ”

“ In any group of human individuals, for example, we can find persons of different stature, different weight, with fingers of different length and form, with heads of different size and shape, hair and eyes of different shades, different blood pressures, pulse rates, digestive possibilities, different degrees of determination, cheerfulness, alertness, and so forth. This fact of variation is not limited to the comparison of the individuals of a given group or generation among themselves, but successive generations considered as the units of comparison show the same sort of thing. ”

“ Additional traits distinguish the units of each Mammalian order; and, again, those of every genus included in it; while others severally characterize the units of each species. Similarly with the varieties in each species, and the stirps in each variety. Now the ability of any component unit to carry within itself the traits of the sub-kingdom, class, order, genus, species, variety, and at the same time to bear the traits of immediate ancestors, can exist only in a something having multitudinous proximate elements arranged in innumerable ways. ”

“ Let us suppose a class of persons, called A, who are afflicted with some form and some specified 82degree of degeneracy, as inferred from personal observations, and from family history, and let class B consist of the offspring of A. We already know only too well that when the grade of A is very low, that of the average B will be below par and mischievous to the community, but how mischievous will it probably be? ”

“ The offspring as a group average lower in grade than their parents—that is, their mean regresses on that of the selected parents, but because of the higher mode about which variation occurs in each generation certain of the offspring are of higher grade than their parents. ”

“ The means of parents and offspring and the other statistical constants for the several generations can be most easily compared by reference to Table 14. Leaving out of consideration the exceptional generation, 2, the following will be observed:
(1) The mean of the selected parents has steadily advanced throughout the series, as has also that of their offspring.
(2) The variability (standard deviation) of the parents as a group has decreased somewhat as increase in numbers made a more rigid selection possible; that of the offspring has undergone a similar change. ”

“ The amount of difference between the several groups—that is the amount of modification which each has undergone—is expressed by such terms as genera, families, orders, and classes. As we have no record of the lines of descent, the pedigree can be discovered only by observing the degrees of resemblance between the beings which are to be classed. ”

“ It will of course be understood that each ascending step of classification is deduced by the same process from the one below. A Genus is a collection of Species which resemble each other more than they 131 resemble other species; an Order is a collection of Genera having, in like manner, the first degree of resemblance, and so on. How close or how wide the Degrees of Resemblance are, must depend upon the nature of the objects compared, and cannot possibly be prescribed beforehand. ”

“ The single objects are called Individuals, because the division cannot be carried farther. The highest class is technically the Summum Genus, or Genus generalissimum; the next highest class to any species is the Proximum Genus; the lowest group before you descend to individuals is the Infima Species, or Species specialissima.
The attribute or attributes whereby a species is distinguished from other species of the same genus, is called its differentia or differentiæ. The various species of houses are differentiated by their several uses, dwelling-house, town-house, ware-house, public-house. ”

“ If then, the results of all the tests that have been made on all mental traits be studied, it will be found that human mental ability as shown in at least 95% of all the traits that have been measured, is distributed throughout the race in various degrees, in accordance with the law of chance, and that if one could measure all the members of the species and plot a curve for these measurements, in any trait, he would get this smooth, continuous curve. ”

“ To those bodies which are sormed by the union of several simple subsiances we gave new names, compounded in such a manner as the nature of the substances directed; but, as the number of double combinations is already very considerable, the only method by which we could avoid confusion, was to divide them into classes. In the natural order of ideas, the name of the class or genus is that which expresses a quality common to a great number of individuals: The name of the species, on the contrary, expresses a quality peculiar to certain individuals only. ”

“ In this definition a large number of attributes have been gathered together in the general term “animal;” then man is separated from the whole class “animal” by the word “reasoning.” A logical definition consists, then, of two parts: the general term naming the genus, and the limiting term naming the distinguishing attribute called the differentia.
Genus and Differentia. Genus and differentia are found in every good definition. The genus should be a term more general than the term defined. “Man is a person who reasons” is a poor definition; because “person” is no more general than “man.” ”

“ In like fashion a series of factors—either of environment or of heredity—if acting equally in both favorable and unfavorable directions, will cause a group of men to form a similar variability curve, when classified according to their relative height. ”

“ The student will see that the process of Classification is two-fold. The first is by Analysis, in which the Genus is divided into Species by reason of differences. The second is by Synthesis, in which individuals are grouped into Species, and Species into the Genus, by reason of resemblances. Moreover, in building up general classes, which is known as Generalization, we must first analyze the individual in order to ascertain its qualities, attributes and properties, and then synthesize the individual with other individuals possessing like qualities, properties or attributes. ”

“ A direct connection is assumed between the visible trait to be favored or eliminated and the characters of the germ cell that are passed on from generation to generation. If the character make the visible trait, rigid selection based on the elimination of traits is the only way of ridding the race of undesirable traits. Improving the condition of individuals would help them, but if traits do not influence characters, such betterments would have no effect on coming generations. ”

“ Every Genus is a Species of the class next higher than itself; and every Species is a Genus of the classes lower than itself. Thus it would seem that the extension in either direction would be infinite. ”

“ Likewise, dominance and recessiveness are as much in evidence, for in tracing back pedigrees of various traits we find the same forms of tabulation that obtain for these conditions in plants and lower animals hold good. For typical cases in man let us use a generalized presence-absence formula and the arbitrary symbol A for the presence of the determiner of the character (double in the individual, single in the germ) and a for its absence. ”

“ Yet there are families in which persons of exceptional ability are unusually frequent. The fact that persons of ability are more frequent in certain families than in the general population of the same social class and with about the same opportunity for the demonstration of inherent ability, gives evidence of its heredity, although we may not be able to summarize the facts under any particular law but must adhere to their statistical expression. ”

“ It is desirable to have names by which to show that one class is contained in another, and, accordingly, we call the class which is divided into two or more smaller ones the genus, and the smaller ones into which it is divided, the species. ”

“ The acquirement of any new unit character would add one more character to the species and double the number of possible varieties or races of the species.
In evolutionary studies we have long recognized that variation was the foundation of evolution and that no evolution was possible without variation, but we have assigned to selection an all-important part as guiding and even stimulating the variation in a certain direction. ”

“ There is a falling back in grade or “regression” of the offspring as compared with their parents, which increases in amount as the grade of the parents becomes higher. (See column “Regression” in Table 1.) The parents of this first generation were chosen because of their high grade. They were all probably in grade above the general average of the population from which they were selected. In the case of those which deviate most from the general average the regression is greatest, as we should expect. ”

“ Genus and Species are superior and inferior classes, and are stated2 to be capable of repeated subordination. The ‘most 106 general Genus’ is the widest class; the ‘most special Species’ the narrowest. Between these are intermediate classes, which are Genera with regard to those below, and Species with regard to those above them. Thus Being is the most general Genus; under this is Body; under Body is Living Body; under this again Animal; under Animal is Rational Animal, or Man; under Man are Socrates and Plato, and other individual men. ”

“ Are Factors Changed Through Selection?
As we have seen, the variation that we find from individual to individual is due in part to the environment; this can generally be demonstrated. Other differences in an ordinary population are recognized as due to different genetic (hereditary) combinations. No one will dispute this statement. But is all the variability accounted for in these two ways? May not a factor itself fluctuate? Is it not a priori probable that factors do fluctuate? ”

“ Every type, we may say, is thus formed by these conditions. To them must be attributed not only the variations in detail which only are commonly called adaptations, but the essential traits of the type, "due also to an anterior adaptation, the effects of which have been transmitted from more or less remote ancestors to their posterity." ”

“ In other words, unless we can find some other basis for this association of traits in a culture, such traits have no functional or other necessary relations to each other.
If we recall the details of trait distribution so far discussed, there come to mind many instances of whole groups of associated traits so segregated as to suggest their diffusion as a whole. In this book we have preferred to use the term trait-complex because it more accurately expresses the character of the phenomenon. For example, we have frequently referred to the maize-complex. ”

“ Why After the First Generation Only Half the Children May Show the Dominant Character.—If the trait is a simple dominant one it is clear that it will appear in each generation and always spring from an affected individual. By referring back to our tabulation of possible matings on page 100 where the dominant character is represented by the letter A, this can be seen at a glance. If the trait is present in the duplex condition in one parent and absent from the other, then formula 3 applies; all children will show the trait, but in the simplex form (Aa) . ”

“ A type is an example of any class, for instance, a species of a genus, which is considered as eminently possessing the characters of the class. All the species which have a greater affinity with this type-species than with any others, form the genus, and are ranged about it, deviating from it in various directions and different degrees."—Whewell, The Philosophy of the Inductive Sciences, vol. ”

“ In the second generation the offspring of extreme variates or fluctuations have not the same average as their own parents [Pg 65] but an average much nearer that of the whole group to which their parents belonged; the average stature of the children of unusually short or tall parents is respectively greater or less than that of their own parents—that is, is nearer the average of the whole group of parents, provided the shortness or tallness of the parents is a fluctuation. ”

“ In our modern societies natural selection has been to some extent suspended; what test have we then of the identity of the most fertile and the most fit? It wants but very few generations to carry the type from the fit to the unfit. ”

“ The more integrated and more differentiated types of the class remain. If in them we find a carrying further of the processes by which the lower types are here supposed to have been evolved, we shall have additional reason for believing them to have been so evolved. If we find that in these superior orders, the individualities of the united segments are much less pronounced than in the inferior, we shall have grounds for suspecting that in the inferior the individualities of the segments are less pronounced than in those lost forms which initiated the annulose sub-kingdom. ”

“ So much work has been done in this subject that we have no hesitation in affirming .5 to represent approximately the average intensity of heredity for physical characters in man. If any well-marked physical character be measured, in which training and environment can not be assumed to have had any part, it will be found, in a large enough number of subjects, that the resemblance, measured on a scale from 0 to 1, is just about one-half of unity. ”