Chapter III - Struggle for Existence
Darwin described in his introductory remarks for this chapter "how species arise in nature;" that is, how "that varieties, which I (Darwin) have called incipient species, become ultimately converted into good and distinct species... (Page 74). He explained that there are slight variations among individuals and varieties and these slight modifications provide benefits, which the individual passes on to its offspring. Because food and water and other resources are limited relative to the number of offspring, there is a struggle for existence and those individuals who inherited beneficial modifications from their parents will have greater chances to survive and reproduce. Darwin further noted:
I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man's power of selection. But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient (Page 75).
Critique
It is now common knowledge from paleontological studies that, unlike the Darwinian model, species appear and disappear abruptly. Aside from changes in size, mammalian species, for example, do not change in their morphology (bone structure) throughout their existence as a species. Thus, according to empirical information, natural selection showed no power to change species morphologies (e.g., Prothero and Heaton 1996 and Eldredge and Gould 1972).
Tattersall (2014:56) noted that the average lifespan of an established mammalian species is 3 to 4 million years. Because our species diverged from a common ancestor shared by modern chimpanzees only 6 to 8 million years ago, there could only be two or three species leaps between us and our simian ancestry. Not Darwinian.
The Term, Struggle for Existence, Used in a Large Sense
Darwin gave examples of his perception of the "struggle for existence" in the natural world. He pointed out that the struggle was not only to assure the life of the individual but also its opportunity to reproduce successfully. He pointed out that predators compete with each other for meat and that plants compete for water and mistletoe berries compete with other fruit for dispersal of seed by fruit-eating animals.
Because wolves and dogs snarl over food and plants without adequate sunshine or water welt and die, the struggle for existence appears obvious. Most school children acknowledge and recognize the "struggle for existence" among plants and animals.
Critique
As noted above, all the obvious snarling and struggle of individuals within and between species failed to impact the morphology of animal species during the life of the species, according to the fossil record.
Geometrical Ratio of Increase
Darwin discussed the tendency of plant and animal populations to increase geometrically. That is, without natural controls on populations of species, the numbers of individuals increase at an increasing rate. Unchecked by predation, disease, or limited natural resources, plants and animals would in a relatively short period of time fill all available space. Darwin's conclusion: "A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase" (Page 76).
Critique
The struggle obvious to Darwin because of the tendency for species to increase geometrically, as noted above, had no power to change the morphology of species that appear in the fossil record during the existence of those species. In other words, the fossil record has failed to produce the numerous intermediate links between species. Species appear abruptly and do not change in bone structure, except for occasional changes in size, for the duration of the species. Microevolutionary selection within extant gene pools and random gene mutations that do not allow the individual to escape the species class could account for changes in size.
Nature of the Checks to Increase
On pages 79-81, Darwin discussed examples of the decimating factors that suppress populations of plants and animals. He provided examples of species populations in the struggle for their existence. He discussed the tendency of species to produce more offspring than the natural resources can sustain in the ensuing struggle for survival.
Critique
Darwin did not present new information here. He previously noted that species produce more offspring than natural resources can sustain and therefore there is a struggle for existence. Under the guise of providing additional information, he noted that because there are predators and disease and limited resources, species must struggle for existence. Of course, he could not have known that future paleontological studies would show that the morphologies of species fail to change over time regardless of the struggles of individuals. Most mammalian species, for example, abruptly disappear intact from the fossil record after a life of 1 to 4 million years (Prothero and Heaton 1996, Eldredge and Gould 1972, Stanley 1979, Tattersall 2014:56).
Complex Relations of All Animals and Plants to Each Other in the Struggle for Existence
Darwin noted that Scotch fir trees were planted on an ungrazed portion of English heath. He was surprised that a host of new species appeared where the Scotch firs were planted. He assumed that the "new" species of plants were somehow associated with the presence of Scotch firs. He believed that there existed some affinity caused by the presence of the Scotch firs that allowed a whole new set of plant species and more vigorous examples of existing plants to appear with the firs. He saw these developments as expressions of complex relations of plants to their environment.
Darwin further noted that when cattle were allowed to graze, they repressed, controlled, and sometimes eliminated the Scotch firs. He believed excessive grazing illustrated the influence of herbivory on plants (a reliable conclusion). He observed that when farmers removed cattle from the pastures, the plants responded positively. These observations illustrated the complexity of relations in nature and provided obvious examples of the struggle for existence.
Darwin said that there was a fly in Paraguay that laid its eggs on the navels of newborn horses and cattle. The maggots of this fly killed the newborn cattle and horses, and thereby prevented feral individuals of those domestic species from occupying large areas. He was likely referring to the screwworm fly (Cochliomyia hominivorax). Darwin believed that the fly controlled the numbers of grazing and browsing animals, which in turn controlled the plant life. He thought that if certain insectivorous birds were to decrease in the area, the flies would become too numerous and would devastate their prey animals, some of which controlled and determined the plant life that was allowed to exist.
It would appear that Darwin's vision of the complex interactions among herbivores, parasites, and plant life provided additional information to emphasize that there had to be an ongoing struggle for existence among species, and that the struggle enabled selective forces to change species into new species.
Critique
As noted by Darwin, the relationships of plants and animals to each other and to their environments are often complex. However, programming of biological information rather than random chance under the direction of natural selection readily explains biological and ecological complexities. Remember, the fossil record, as redundantly stated above, shows species appear and disappear abruptly without gradual, step-wise changes.
Struggle for Life Most Severe between Individuals and Varieties of the Same Species
Plants and animals most similar in their structure, physiological needs, and behavior are most likely to compete with each other when resources are limited. This statement appears obvious and logical. Under this topic, Darwin cited several examples of closely related species displacing each other. In consolation, Darwin attempted to ease his harsh vision of nature's war for survival:
When we reflect on this struggle, we may console ourselves with the full belief that the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply (Page 87).
Critique
Darwin
gave examples of species displacing other species but provided no examples of species turning into other species. He also failed to note that species often disappear rapidly, not because of competition among species but because new predators appear; e.g., microbes.
It is not clear how Darwin knew that animals being killed experience no fear. Perhaps the fearlessness of animals was another one of his numerous "rules" or "laws" or "principles" of nature.