The History of the Development of Biological Thought

Like Darwin, Wallace was suddenly inspired by Malthus's theory of population. Careful reading of Wallace's 1858 article

Like Darwin, Wallace was suddenly inspired by Malthus's theory of population. Careful reading of Wallace's 1858 article "On the Tendency of Varieties to Separate Unlimitedly from the Original" shows, however, that the resemblance is not quite identical. Wallace made his point very clear: "There is a universal law in nature that makes many varieties live longer than others, and produce successive variations, which are farther and farther away from the original species.". Wallace is still using pattern language here, but his conclusion is quite clearly the opposite of Lyell's assertion that "varieties are strictly delimited, and their variations must not be more different from the original species." The most important aspect of Wallace's analysis is that he is careful not to get bogged down in the morass of morphological controversies about species and varieties, but to ground his conclusions in very strict ecological arguments. He concluded that the population size (number) of a species was not determined by fecundity at all, but by the natural containment of potential population growth. A large number of animals must die every year to keep the population stable, and "those who die must be the weakest, that is, the small, the old,needle valve manufacturer, and the sick; those who continue to live can only be the best in health and energy, that is, those who are most able to take food normally and defend themselves against innumerable enemies.". As we said at the beginning, this is a "competition for survival," in which the weakest and least structured must die " (pp. 56-57). In an earlier part of his article,ball valve manufacturer, Wallace focused on population size (number) control, stabilizing selection (culling), and competition between species. Then he "went on to discuss variants, and the comments that preceded the discussion of variants were used directly and importantly." In the discussion that follows, Zhonghua Laitu applies the term "variety" to individuals that are variants, that is, individuals in a population that do not share the same properties. If a species produces a better variety, "sooner or later that variety must be numerically dominant." (58 pages). Curiously, Wallace's formulation suffers from the same weaknesses as Darwin's. There are still many model ideas, especially when it comes to the nature of varieties, 12 needle valve ,tube fitting manufacturer, which is similar to Darwin's, and he still acknowledges the widespread view of use, advance and retreat at that time. Like Darwin, Wallace once explicitly objected to "Lamarck's hypothesis" in an article, pointing out that it came directly from Leier. He explained the short, retractable claws of the cat and the long neck of the giraffe in strict selectionist terms. Wallace strongly emphasized that the acquisition of new adaptive traits was entirely consistent with the interpretation that they were the result of selection. He concluded his article with the following passage: We believe that we have now proved that certain types of varieties in nature have a tendency to progress farther and farther away from the original species, and that there seems to be no reason to assign specific limits to this progress.. This progress, in small steps and in different directions, is always contained and balanced by the necessary conditions, which alone can sustain survival. This progress is supposed to be able to follow through in order to be consistent with all the phenomena that living things exhibit, such as their extinction and continuation in past times, and the extraordinary changes in form, instincts, and habits that they exhibit (p. 62). Let us try here to compare in more detail the lines of Wallace's and Darwin's arguments. Both of them started from the problem of species, or as Wallace himself said in a retrospective article in 1908, with the idea of exploring "the possible causes of species change". Although Wallace's analysis of the problem is to some extent more focused on the study of population ecology than on speciation (which he probably thought he had fully discussed in 1855). Unlike Darwin, Wallace connects the problem of evolution to humans very directly. He had spent eight years living with indigenous peoples, and the question of what constraints had kept "the population of all uncivilized indigenous peoples basically stable" had long puzzled him. These restraining factors (disease, famine, accidents, and war, as listed by Malthus) are the causes of population decline. It suddenly occurred to me that for wild animals, the effects of these constraints would be even harsher. All lower animals proliferate faster than humans, while their populations generally remain the same. The idea of the survival of the fittest flashed through my mind for a moment (Wallace, 1903:78). As with Darwin, a key component of evolution by natural selection is the recognition of individuality. Exactly 50 years later (1908), Wallace said of this, "Just as Darwin suddenly remembered years ago, certainty suddenly crossed my mind that those who survived this decorative destruction year after year must have some slight superiority on the whole." This slight superiority allows them to escape every particular form of death (in which most of them die), that is to say, in the famous formula, the fittest will survive. I understood at once that the ever-present variability of all living things would provide the material needed. As has been said before, there is a subtle difference between Wallace's and Darwin's explanations. Wallace was clearly more impressed by Malthus's general thesis,38 tube fitting, especially the "determined resistance" to keep the population at a stable level of mass deaths each year. The idea of populations in natural selection comes from different sources in both of them. From the study of animal breeding and classification in the case of Darwin, and from the study of human population and classification in the case of Wallace. Wallace downplayed the value of the study of livestock varieties and asserted that "no inferences can be drawn about varieties in their natural state" from the observation of livestock. For this and other reasons, he does not use the word "choice" in his articles and always seems to have a soft spot for it.


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