Population (biology)

“ It was part of the animal movement which was establishing biological centres, determining geographical range, bringing too the sparse population of the world into a heterogeneous distribution, by which the world itself might become more quickly peopled. ”

“ Population And Emigration.
Both in the vegetable and animal kingdoms every species derives from nature a reproductive faculty beyond the demand for merely keeping up its stock; the seed of a single plant is sufficient to multiply it one hundred or a thousand fold. The animal offspring is never limited to the number of its parents. ”

“ Yet it is doubtful if the slightest change in the population of a biologic province can be brought about without some effect upon all the members of the society. It is a vast, sensitive thing, fit to be compared with the living body where every cell lives in accord with every other of the frame. ”

“ If, therefore, we were to divide the population of any species into three groups of equal extent, with regard to any particular character—as length of wing, or of toes, or thickness or curvature of bill, or strength of markings—we should have one group in which the mean or average character prevailed with little variation, one in which the character was greatly, and one in which it was little, {60}developed. ”

“ In the earlier stages of human history, population is limited mainly by biologic factors. The biologic stage continues so long as there are no artificial restraints put on the birth-rate, and no deliberate destruction of offspring for the purposes of limiting the size of the family. There the limits are all objective; they are found in scantiness of the food-supply, or in destruction by enemies, animal or human. Each species has an average or normal birth-rate, great or small. ”

“ In each area we shall find a population obviously related to every other, but each will constitute a population whose limits of variation are different from those of any other. Sometimes these limits overlap, sometimes they are wholly within, sometimes they are wholly without the limits for each other species. Sometimes the populations are wholly segregated by mountain crests and divides, sometimes the populations hybridize and intergrade over broad zones of transition; but always each population is distinct in a great area which is the heart of the range of each species. ”

“ In a remarkable essay on the Theory of Population, Herbert Spencer has shown, by an elaborate discussion of the phenomena presented by the whole animal kingdom, that the maintenance of the individual and the propagation of the race vary inversely, those species and groups which have the shortest and most uncertain lives producing the greatest number of offspring ”

“ The three sets of figures in the left-hand column indicate different positions of equilibrium in a population consisting of homozygous dominants, heterozygous dominants, and recessives. The remaining columns indicate the number of generations in which a population will pass from one position of equilibrium to another, under a given intensity of selection. ”

“ The conditions of propagation among plants and animals, the results of their multiplication, vary according to circumstances; and man with his experiments in breeding does not correct Nature, he only copies her. It is plainly out of the question here to speak of laws of population; it were better instead to say that the conditions of population in each period are the effects of special, variable causes peculiar to each stage of development. Cases which are the result of varying circumstances and events are not laws, nor do they justify us in inferring fixed laws. ”

“ As a fact, more than half the whole population of most species seems to vary to a perceptible and measurable, and therefore sufficient, amount in scores of ways. Take a species with a million pairs of individuals—half of these vary sufficiently, either + or -, in the four acquired characters A, B, C, D: what will be the proportion of individuals that vary + in these four characters [pg 051] according to the law of averages? Will it not be about 1 in 64? If so it is ample—in many cases—for Natural Selection to work on, because in many cases less than 1/64 of offspring survives. ”

“ The facts of the distribution of local forms on the whole are consistent with the view that these forms come into existence by the sporadic appearance of varieties in a population, rather than by transformation of the population as a whole. ”

“ It is an existent, tremendous population of living individuals whose identities and dissimilarities, whose divergences from all other populations, whose origin in some remote past and extension thru actual generations and years of time, whose position on these particular trees in these particular valleys and everywhere over these miles of actual country—it is this reality which, to us, constitutes the species problem. ”

“ Or, let us suppose that man, the dominant species, originated from a single pair, only 100,000 years ago, the shortest period suggested by any evolutionist (and much too short for evolution) and that the population doubled in 1612.51 years, one-tenth the Jewish rate of net increase, a most generous estimate. The present population of the globe should be 4,660,210,253,138,204,300 or 2,527,570,733 for every man, woman and child! In these calculations, we have made greater allowances than any self-respecting evolutionist could ask without blushing. ”

“ Ten years ago, the non-temps will tell you, the population of Earth was one billion, far smaller than it was in the past because of a sensible policy of eugenics. Today the population is somewhat short of a billion, they say, and the census verifies it. ”

“ Therefore, the rules are that large areas turn out an absolutely greater number of specific types than small areas; although, relatively to the number of individuals or amount of population, the small areas turn out a larger number of species than the large areas. ”

“ I had for some time been aware that population and food increased in different ratios, and a vague opinion had been floating in my mind that they could only be kept equal by some species of misery or vice, but the perusal of Dr Price's two volumes of Observations, after that opinion had been conceived, raised it at once to conviction. ”

“ Thus, if the existence of a small number of distinct races of mankind be taken as a starting-point, it is obvious that their crossing would produce an indefinite number of secondary varieties, such as the population of the world actually presents. ”

“ If it really be, as he declares, that population tends to increase in a geometrical ratio, while the food-supply increases only in an arithmetical ratio, his conclusion, that population has a constant tendency to run ahead of subsistence, seems inevitable. ”

“ It follows that at any given time, in any given country, the advantageous variations always present are not to be counted by ones and twos, as stated by Lord Salisbury, but by scores of millions; and not in individuals widely apart from each other, but constituting in every locality or country, somewhere about one half of the whole population of the species. ”

“ Then the rapidity of multiplication came into play, so that in two or three years the population of each species became as great as ever; while, as all the least favorable variations had been destroyed, the species as a whole had become better adapted to its environment than before the almost catastrophic destruction of such a large proportion of them. ”

“ Even the least prolific of animals would increase rapidly if unchecked, whereas it is evident that the animal population of the globe must be stationary, or perhaps, through the influence of man, decreasing. ”

“ With so many facts in his view, to prove the extraordinary rapidity with which population increases, when unchecked; and with such a body of evidence before him, to elucidate, even the manner, by which the general laws of nature repress a redundant population ”

“ From the beginning of the century, the inflow averaged little less than a million a year, and while about one-fifth of this represented a temporary migration, four-fifths of it meant a permanent addition to the population of the New World. ”

“ In instances of this kind the powers of the earth appear to be fully equal to answer it the demands for food that can be made upon it by man. But we should be led into an error if we were thence to suppose that population and food ever really increase in the same ratio. ”

“ In like manner the increase of the number of human beings—if calculated on the average proportion of births to population, and no hindrances to the natural increase stood in the way—would be such as to double the total in twenty-five years. ”

“ From yet another perspective—that of, say, population genetics—neither of these systems might be taken to be an individual; while a population geneticist might well be interested in brain-containing systems, she will take something like alleles to be her primary objects, and will discern patterns in the evolution of systems from that perspective. ”

“ Ecology had estimated the native human population not to exceed three million people over the entire globe, and cheerfully admitted that their estimate was made with every benefit of doubt given to the natives. ”

“ I proposed to consider, in this and in the following Lecture, the checks to population.
We have seen that the increase of food cannot keep pace with the theoretical rate of increase of population. Since, therefore, food is essential to the existence of man, it is obvious, that, with reference to the increase of numbers actually possible, the theoretical power of multiplication can be of little moment, and that, whatever be its extent, the actual excess of the births above the deaths must be determined according to the inferior progression of the supply of food. ”

“ Demography, which is to be discriminated from statistics as a method. The latter renders service to all social sciences in so far as their phenomena may be represented quantitatively. Demography, or the science of population, has a concrete content and infers conclusions. ”

“ Whatever resemblance certain of these species bear to those of our days, it cannot be disputed that the general mass of this population had a very different character, and that the greater part of the races which composed it have been utterly destroyed. ”

“ On the other hand, there is a scarcity of literature from the biological standpoint, I do not know of any place in print where a biologist has attempted to advance a definite and complete theory of population, and in arriving at the biological explanation of the diminishing birth rate I have been dependent upon stray hints found here and there and especially upon information gained by conversation with two of my colleagues, one a zoologist and the other a botanist. There is no body of doctrine upon population to which biologists subscribe at all comparable to that among economists. ”

“ On the other hand, large and continuous areas are favourable to the production of numerous species, first, because they contain a large population, thus favouring the occurrence of numerous variations; and, secondly, because the large area furnishes a diversity of conditions in its different parts, as to food, climate, attitude, &c., and thus so many different opportunities for the occurrence of sundry forms of homogamy. ”

“ But since the population of this imaginary area has reached the maximum, and the supply of food, though limited in distribution, is nevertheless plentiful, such movements will be irregular and will proceed in no definite direction. ”

“ Taking the population of the world at any number, a thousand millions, for instance, the human species would increase in the ratio of—1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. and subsistence as—1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. In two centuries and a quarter, the population would be to the means of subsistence as 512 to 10: in three centuries as 4096 to 13, and in two thousand years the difference would be almost incalculable, though the produce in that time would have increased to an immense extent. ”

“ The number of human beings now peopling the earth is supposed to amount to eight hundred millions, so that we may easily understand how great a number of beasts of prey, birds, and animals of every class, this prodigious population must have displaced, independently of the still more important consequences which have followed from the derangement brought about by man in the relative numerical strength of particular species. ”

“ My belief certainly is that number of offspring is not so important an element in keeping up population of a species as supply of food and other favourable conditions; because the numbers of a species constantly vary greatly in different parts of its own area, whereas the average number of offspring is not a very variable element. ”

“ Darwin knew that if selection of particular kinds of individuals of a population takes place the next generation is affected. If the taller men of a community are selected the average of their offspring will be taller than the average of the former population. If selection for tallness again takes place, still taller men will on the average arise. ”

“ The transformation of masses of population by imperceptible steps guided by selection, is, as most of us now see, so inapplicable to the facts, whether of variation or of specificity, that we can only marvel both at the want of penetration displayed by the advocates of such a proposition, and at the forensic skill by which it was made to appear acceptable even for a time. ”

“ On this condition only does the process of organization appear possible. We might almost say that just as some race of animals, which multiplies and spreads into divers regions of the earth, becomes differentiated into several races through the adaptation of each to its conditions of life; so, the originally homogeneous population of cells arising in a fertilized germ-cell, becomes divided into several populations of cells that grow unlike in virtue of the unlikeness of their circumstances. ”