CYTOLOGY (cell word), the study of the cell, the const.i.tuent unit of organisms.
DETERMINER (completely end), an element or condition in a germ-cell, supposed to be essential to the development of a particular quality, feature, or manner of reaction of the organism which arises from that germ-cell. The word is gradually falling into disuse, and "factor" taking its place.
DOMINANCE (mastery), in Mendelian hybrids the capacity of a character which is derived from only one of two generating gametes to develop to an extent nearly or quite equal to that exhibited by an individual which has derived the same character from both of the generating gametes. In the absence of dominance the given character of the hybrid usually presents a "blend" or intermediate condition between the two parents.
DYSGENIC (bad origin), tending to impair the racial qualities of future generations; the opposite of eugenic.
ENDOGAMY (within mating), a custom of some primitive peoples, in compliance with which a man must choose his wife from his own group (clan, gens, tribe, etc.).
EUGENIC (good origin), tending to improve the racial qualities of future generations, either physical or mental.
EUTHENIC (good thriving), tending to produce beneficial acquired characters or better conditions for people to live in, but not tending (except incidentally and indirectly) to produce people who can hand on the improvement by heredity.
EVOLUTION (unroll), ORGANIC, the progressive change of living forms, usually a.s.sociated with the development of complex from simple forms.
EXOGAMY (out mating), a custom of primitive peoples which requires a man to choose a wife from some other group (clan, gens, tribe, etc.) than his own.
FACTOR (maker), a name given to the hypothetical _something_, the independently inheritable element in the germ-cell, whose presence is necessary to the development of a certain inherited character or characters or contributes with other factors to the development of a character. "Gene" and "determiner" are sometimes used as synonyms of factor.
FEEBLE-MINDEDNESS, a condition in which mental development is r.e.t.a.r.ded or incomplete. It is a relative term, since an individual who would be feeble-minded in one society might be normal or even bright in another. The customary criterion is the inability of the individual, because of mental defect existing from an early age, to compete on equal terms with his normal fellows, or to manage himself or his affairs with ordinary prudence. American students usually distinguish three grades of mental defect: Idiots are those who are unable to take care of themselves, even to the extent of guarding against common physical dangers or satisfying physical needs. Their mentality does not progress beyond that of a normal two-year-old child. Imbeciles can care for themselves after a fashion, but are unable to earn their living. Their mental ages range from three to seven years, inclusive. Morons, who correspond to the common acceptation of the term feeble-minded, "can under proper direction become more or less self-supporting but they are as a rule incapable of undertaking affairs which demand judgment or involve unrestricted compet.i.tion with normal individuals. Their intelligence ranges with that of normal children from seven to twelve years of age." There is necessarily a considerable borderline, but any adult whose intelligence is beyond that of the normal twelve-year-old child is usually considered to be not feeble-minded.
GAMETE (mate), a mature germ-cell; in animals an ovum or spermatozoon.
GENETICS (origins), for a long time meant the study of evolution by experimental breeding and was often synonomous with Mendelism. It is gradually returning to its broader, original meaning of the study of variation and heredity, that is, the origin of the individual"s traits. This broader meaning is preferable.
GERMINAL (sprig), due to something present in the germ-cell. A trait is germinal when its basis is inherited,--as eye color,--and when it develops with nothing more than the standard environment; remaining relatively constant from one generation to another, except as influenced by reproduction.
GERM-PLASM (sprig form), mature germ-cells and the living material from which they are produced.
HaeMOPHILIA (blood love), an inability of the blood to clot. It thus becomes impossible to stop the flow of blood from a cut, and one who has inherited haemophilia usually dies sooner or later from haemorrhage.
HEREDITY (heirship), is usually considered from the outside, when it may properly be defined as organic resemblance based on descent, or the correlation between relatives. But a better definition, based on the results of genetics, looks at it as a mechanism, not as an external appearance. From this point of view, heredity may be said to be "the persistence of certain cell-const.i.tuents (in the germ-cells) through an unending number of cell-divisions."
HETEROZYGOTE (different yolk), a zygotic individual which contains both members of an allelomorphic pair.
h.o.m.oZYGOTE (same yolk), an individual which contains only one member of an allelomorphic pair, but contains that in duplicate, having received it from both parents. A h.o.m.ozygous individual, having been formed by the union of like gametes, in turn regularly produces gametes of only one kind with respect to any given factor, thus giving rise to offspring which are, in this regard, like the parents; in other words, h.o.m.ozygotes regularly "breed true." An individual may be a h.o.m.ozygote with respect to one factor and a heterozygote with respect to another.
HORMONES (chain), the secretions of various internal glands, which are carried in the blood and have an important specific influence on the growth and functioning of various parts of the body. Their exact nature is not yet understood.
INBORN usually means germinal, as applied to a trait, and it is so used in this book. Strictly speaking, however, any trait which appears in a child at birth might be called inborn, and some writers, particularly medical men, thus refer to traits acquired in prenatal life. Because of this ambiguity the word should be carefully defined when used, or avoided.
INHERENT (in stick), as used in this book, is synonymous with germinal.
INDUCTION (in lead), a change brought about in the germ-plasm with the effect of temporarily modifying the characters of an individual produced from that germ-plasm; but not of changing in a definite and permanent way any such germ-plasm and therefore any individual inherited traits.
INNATE (inborn), synonymous with inborn.
LATENT (lie hidden), a term applied to traits or characters whose factors exist in the germ-plasm of an individual, but which are not visible in his body.
LAW, in natural science means a concise and comprehensive description of an observed uniform sequence of events. It is thus quite different from the law of jurists, who mean a rule laid down for the guidance of an intelligent being, by an intelligent being having power over him.
MENDELISM, a collection of laws of heredity (see Appendix D) so-called after the discoverer of the first of them to become known; also the a.n.a.lytical study of heredity with a view to learning the const.i.tution of the germ-cells of animals and plants.
MENDELIZE, to follow Mendel"s laws of inheritance.
MORES (customs), the approved customs or unwritten laws of a people; the conventions of society; popular usage or folk-ways which are reputable.
MUTATION (change), has now two accepted meanings: (1) a profound change in the germ-plasm of an organism such as will produce numerous changes in its progeny; and (2) a discontinuous heritable change in a Mendelian factor. It is used in the first sense by De Vries and other "mutationists" and in the second sense by Morgan and other Mendelists; confusion has arisen from failure to note the difference in usage.
NORMAL CURVE, the curve of distribution of variations of something whose variations are due to a multiplicity of causes acting nearly equally in both directions. It is characterized by having more individuals of a mediocre degree and progressively fewer above and below this mode.
NUCLEUS (little nut), a central, highly-organized part of every living cell, which seems to play a directive role in cell-development and contains, among other things, the chromosomes.
PATENT (lie open), a term applied to traits which are manifestly represented in the body as well as the germ-plasm of an individual. The converse of "latent."
PROBABILITY CURVE, the same as normal curve. Also called a Gaussian curve.
PROTOPLASM (first form), "the physical basis of life"; a chemical compound or probably an emulsion of numerous compounds. It contains proteins which differ slightly in many species of organism. It contains carbon, hydrogen, oxygen, nitrogen, sulphur, and various salts, but is so complex as to defy exhaustive a.n.a.lysis.
PSYCHIATRY (soul healing), the study of diseases of the mind.
RECESSIVE (draw back), the converse of dominant; applied to one of a pair of contrasted Mendelian characters which can not appear in the presence of the other.
REGRESSION (back go), the average variation of one variable for a unit variation of a correlated variable.
SEGREGATION (aside flock), (1) as used in eugenics means the policy of isolating feeble-minded and other anti-social individuals from the normal population into inst.i.tutions, colonies, etc., where the two s.e.xes are kept apart. (2) The term is also used technically in genetics, to refer to the discontinuity of the variation of characteristics resulting from the independent distribution of factors before or at the time of formation of the gametes.
SELECTION (apart pick), the choice (for perpetuation by reproduction) from a mixed population, of the individuals possessing in common a certain character or a certain degree of some character. Two kinds of selection may be distinguished: (1) natural selection, in which choice is made automatically by the failure to reproduce (through death or some other cause) of the individuals who are not "fit" to pa.s.s the tests of the environment (vitality, disease resistance, speed, success in mating, or what not); and (2) artificial selection, in which the choice is made consciously by man, as a livestock breeder.
s.e.x-LIMITED, a term applied to traits which differ in the two s.e.xes, because influenced by the hormones of the reproductive glands.
Example, the beard.
s.e.x-LINKED, a term applied to traits which are connected with s.e.x _accidentally_ and not physiologically in development. The current explanation is that such traits happen to be in the same chromosome as the determiner of maleness or femaleness, as the case may be.
Color-blindness is the cla.s.sical example in man.
s.e.xUAL SELECTION, the conscious or unconscious preference by individuals of one s.e.x, or by that s.e.x as a whole, for individuals of the other s.e.x who possess some particular attribute or attributes in a degree above or below the average of their s.e.x. If the deviation of the chosen character is in the same direction (plus or minus) as in the chooser, the mating is called a.s.sortative; if in one direction independent of the characteristic of the chooser, it is called preferential.
SOMA (body), the body as distinguished from the germ-plasm.
From this point of view every individual consists of only two parts,--germ-plasm and soma or somatoplasm.
TRAIT, a term used by geneticists as a synonym of "character."
UNIT-CHARACTER, in Mendelian heredity a character or alternative difference of any kind, which is apparently not capable of subdivision in heredity, but is inherited as a whole, and which is capable of becoming a.s.sociated in new combinations with other characters. The term is now going out of use, as it makes for clearer thinking about heredity to fix the attention on the factors of the germ-cells instead of on the characters of the adult.
VARIATION, a deviation in the size, shape, or other feature of a character or trait, from the mean or average of that character in the species.
VESTIGIAL (footstep), a term applied to a character which at some time in the evolutionary history of the species possessed importance, or functioned fully, but which has now lost its importance or its original use, so that it remains a mere souvenir of the past, in a degenerated condition. Example, the muscles which move a man"s ears.
ZYGOTE (yolk), the fertilized egg-cell; the united cell formed by the union of the ovum and spermatozoon after fertilization.