Struggle for existence

Population increase causing the struggle for existence was given numerical expression by Buffon in 1751. He calculated that an elm seed would produce a tree which, after 10 years, produced 1,000 seeds. If each were sown, the whole globe would be converted into trees in 150 years. Similarly, "if we were to hatch every egg produced by hens for a space of 30 years, there would be a sufficient number of fowls to cover the whole surface of the earth." Taking the example of herrings, if "prodigious numbers of them were not destroyed" each year they would soon cover the surface of the sea, but they would then be destroyed by "contagion and famine", so it was necessary and right that animals preyed on each other.[14]

Amidst debates on fears of British depopulation, Benjamin Franklin collected statistics of the American colonies which he published in his Poor Richard Improved of 1750 with the question of "how long will it be, before by an Increase of 64 per Annum, 34,000 people will double themselves?" He concluded: "People increase faster by Generation in these Colonies, where all can have full Employ, and there is Room and Business for Millions yet unborn. For in old settled Countries, as England for instance, as soon as the Number of People is as great as can be supported by all the Tillage, Manufactures, Trade and Offices of the Country, the Over-plus must quit the Country, or they will perish by Poverty, Diseases, and want of Necessaries. Marriage too, is discouraged, many declining it, till they can see how they shall be able to maintain a Family." In 1751, Franklin wrote his Observations Concerning the Increase of Mankind, Peopling of Countries, etc. proposing a 25-year doubling period in the colonies, an exponential growth in population. Over the following century, this forecast was remarkably accurate. His paper was widely circulated, and had considerable influence: Malthus cited the period as "a rate in which all concurring testimonies agree."[15] Franklin's view was optimistic:

There is, in short, no bound to the prolific nature of plants or animals, but what is made by their crowding and interfering with each other's means of subsistence. Was the face of Earth vacant of other plants, it might be gradually sowed and overspread with one kind only, as, for instance, with fennel; and, were it empty of other inhabitants, it might in a few ages be replenished from one nation only, as, for instance, with Englishmen.[16]

Those migrating to America would "have their places at home soon supplied" and "increase so largely here" that there was no need for other immigrants.[16]

Natural theology continued an earlier theme of harmonious balance between plants and animals. In the late 18th century, naturalists saw the struggle for existence as part of an ordered balance of nature, but they increasingly recognised the fierceness of struggle and the fossil record shook ideas of permanent harmony. Carl Linnaeus saw an overall benign balance, but also showed calculations of the Earth quickly filling with one species if it reproduced unchecked,[17] and referred to "bellum omnium perpetuum in omnes, et horrenda laniena" (a perpetual war of all against all, and horrible massacre).[18]

In 1773 James Burnett, Lord Monboddo, noted that "the most fruitful country can be overstocked with any animal and particularly with man", and "when men were so multiplied that the natural fruits of the earth could not maintain them", they could emigrate, prey on other animals or each other, or preferably "associate and provide in common what singly they could not procure." In 1775 Kant visualised inner and outer struggle as the impetus for man passing from a rude state of nature to a citizen, Herder in 1784 saw a personified Nature promoting huge numbers of organisms competing for resources so that "the whole creation is at war", crowding "her creatures one upon another" to "produce the greatest number and variety of living beings in the least space, so that one crushes another, and an equilibrium of powers can alone bring peace to the creation." For William Smellie in 1790 a profusion of animal life improved "in proportion to the number of enemies they have to attack or evade", and by making animals feed upon each other, the system of animation and of happiness is extended to the greatest possible degree. In this view, Nature, instead of being cruel and oppressive, is highly generous and beneficent."[19]

Erasmus Darwin in his Temple of Nature (published 1803) returned to Linnaean imagery, "From Hunger's arms the shafts of Death are hurl'd; And one great Slaughter‐house the warring world!"[18][20]

The term struggle for existence was already in use by this time.[17] For example, in 1790 Jeremy Bentham proposed reformed elections as "a contest for distinction, not a struggle for existence",[21] and in 1795 The Monthly Review used it to describe trees when discussing Thomas Cooper's Some Information Respecting America.[22] In a House of Lords speech on 2 November 1797, Lord Gwydir said they were engaged "in a struggle for existence as a nation" in the French Revolutionary Wars.[23] Benjamin Disraeli included the phrase "a density of population implies a severe struggle for existence" in his novel Sybil (1845), which was about the plight of the working class in Britain.

Malthusian curve. Thomas Robert Malthus argues that a population will increase exponentially if unchecked, while resources will only increase arithmetically.

In An Essay on the Principle of Population, Thomas Robert Malthus argues that a population will increase exponentially if unchecked, while resources will only increase arithmetically.[3] This is seen graphically in the adjacent image and is commonly referred to as the Malthusian curve. Malthus knew that with limited resources on earth, there would be competition among people to exist and survive. He coined the phrase the Malthusian catastrophe to explain how there were positive checks in human populations like famine and disease that kept the population from rising too quickly.[24] The checks that exist on the human population growth result in a struggle for existence.[3] Malthus also notes that the checks on the human population are more complicated than those on animals and plants.[25] Malthus explains, for example, that a human check on population growth is the conscious decision not to reproduce because of financial burden.[25] Malthus then explains that the main check on population growth is food. In periods of high food availability the population increases, while in periods of food shortages, the population decreases.[26] Thus, "population [growth] tends to oscillate around its means of subsistence."[27] The combination of Malthus' "law of multiplication in geometrical progression" and "the law of limited population" leads to the idea of the struggle for existence.[3] Despite these ideas, Malthus was a religious man and believed in divine laws that governed the natural world.[2]

In 1832, Augustin Pyramus de Candolle concisely described the struggle between species of plants in a chapter about parasitism. His friend Charles Lyell quoted this passage in the second volume of Principles of Geology:[28]

"All the plants of a given country," says Decandolle in his usual spirited style, "are at war one with another. The first which establish themselves by chance in a particular spot, tend, by the mere occupancy of space, to exclude other species—the greater choke the smaller, the longest livers replace those which last for a shorter period, the more prolific gradually make themselves masters of the ground, which species multiplying more slowly would otherwise fill."

In this volume, Lyell strongly defended his view that species were fixed against ideas of transmutation of species. To explain adaptation, Lamarck proposed that species did not become extinct, but constantly transformed to suit a changing environment: Lyell believed in essentialism in which species were fixed so could not adapt to change, and became extinct.[29] Hybrids had been proposed as evidence of transmutation; Lyell argued that they would not survive to make new species.[30]

If we consider the vegetable kingdom generally, it must be recollected, that even of the seeds which are well ripened, the greater part are either eaten by insects, birds, and other animals, or decay for want of room and opportunity to germinate. Unhealthy plants are the first which are cut off by causes prejudicial to the species, being usually stifled by more vigorous individuals of their own kind. If, therefore, the relative fecundity or hardiness of hybrids be in the least degree inferior, they cannot maintain their footing for many generations, even if they were ever produced beyond one generation in a wild state. In the universal struggle for existence, the right of the strongest eventually prevails; and the strength and durability of a race depends mainly on its prolificness, in which hybrids are acknowledged to be deficient.

In the late 1830s, Charles Darwin began developing his ideas of "warring of the species" leading to natural selection.

Charles Darwin initially shared the belief that nature was perfect and harmonious:[2] after graduating as a student at the University of Cambridge in 1831, he was convinced by William Paley's Natural Theology or Evidences of the Existence and Attributes of the Deity which saw adaptation as purposeful design and presented population pressure optimistically; "it is a happy world after all".[31] By mid January 1832, early in the Beagle voyage, Darwin saw geology from Charles Lyell's viewpoint. When the second volume of Lyell's Principles of Geology was delivered to the Beagle that November, Darwin accepted its argument that the "struggle for existence" disproved transmutation of species. He was reminded of Malthusianism when his sisters sent him out pamphlets by Harriet Martineau.[32] Lyell had been unable to show the mechanism for introducing new species, and towards the end of the voyage Darwin noted that the distribution of mockingbirds found on the Galápagos Islands raised doubts that species were fixed.[33]

Early in 1837 John Gould in London revealed that the mockingbirds were separate species: Darwin was spurred into intensive research and the inception of his theory to find the mechanism introducing species. Unconventionally, he sought information from animal breeders. In September 1838, while investigating variation, averages and population statistics, he read Malthus’ An Essay on the Principle of Population,[34] and wrote:

We ought to be far from wondering of changes in numbers of species, from small changes in nature of locality. Even the energetic language of Malthus Decandolle does not convey the warring of the species as inference from Malthus. — increase of brutes must be prevented solely by positive checks, excepting that famine may stop desire. — in nature production does not increase, whilst no check prevail, but the positive check of famine & consequently death. Population is increase at geometrical ratio in far shorter time than 25 years — yet until the one sentence of Malthus no one clearly perceived the great check amongst men[35]

That sentence is on page 6 of the first volume of Malthus' Essay, 6th edition: "It may safely be pronounced, therefore, that the population, when unchecked, goes on doubling itself every twenty five years, or increases in a geometrical ratio."[35] At first Darwin suggested species competing for resources, six months later he saw competition between individuals of the same species:[36] in mid March 1839 he wrote of the "dreadful but quiet war of organic beings. going on the peaceful woods. & smiling fields" in which "a grain of sand turns the balance",[37] a month later he wrote, of the "innumerable seeds" of a bulrush, "if a seed were produced with infinitesimal advantage it would have better chance of being propagated".[38] He began to see a similarity between farmers selecting breeding livestock and what he came to call natural selection, still thinking of this as a benevolent law ordained to create adaptation.[39]

In his 1842 sketch expanding his theory, Darwin wrote that "De Candolle's war of nature,—seeing contented face of nature,—may be well at first doubted", but "considering the enormous geometrical power of increase in every organism" countries "must be fully stocked" referring to "Malthus on man": later in the sketch he used the phrase "struggle of nature", and on the back of one sheet "struggle of existence". In his 1844 Essay Darwin began his section on Natural Means of Selection with "De Candolle, in an eloquent passage, has declared that all nature is at war, one organism with another, or with external nature", and described this "war" as "the doctrine of Malthus applied in most cases with ten-fold force." In later sections, including the summary, he used the phrase "struggle for existence",[40] which he had read in several books including Lyell's Geology. On 3 March 1857 he wrote chapter 5 of his "big book" on his theory, initially headed "On Natural Selection". The relevant section, titled "Struggle of Nature" had as an alternative title "War of Nature". At a later date he changed the chapter heading to "The Struggle For Existence As Bearing On Natural Selection" and made the section title "The Struggle for existence", making this his main theme to allow a broader interpretation than one of war between organisms: he used the phrase "in a very large sense" to include mutual dependency and the physical environmental as when "a plant on the edge of a desert is often said to struggle for existence" due to its need for moisture.[41]

In his "Abstract" of his book, quickly written and published as On the Origin of Species in 1859, Darwin made his third chapter "Struggle for Existence" . After "a few preliminary remarks" relating it to natural selection, and acknowledgement that the "elder De Candolle and Lyell have largely and philosophically shown that all organic beings are exposed to severe competition",[42] he wrote that:

A struggle for existence inevitably follows from the high rate at which all organic beings tend to increase [so that] on the principle of geometrical increase, its numbers would quickly become so inordinately great that no country could support the product. Hence, as more individuals are produced than can possibly survive, there must in every case be a struggle for existence, either one individual with another of the same species, or with the individuals of distinct species, or with the physical conditions of life. It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms".[42]

Darwin gradually included the idea that adaptations were not from birth, but rather from external pressures.[3] This describes Darwin's change from teleological explanation to transmutationist thought which was influential the change in Darwin's understanding of nature from 1837 to the 1850s.[43] From Malthus, Darwin claims that the idea of a struggle for existence allowed him to see that favorable variations would be preserved while unfavorable variations would not resulting in the evolution new species.[3] Thus, by the spring of 1837, Darwin had changed from supporting the idea that each species was independently created to supporting the notion that each species was descended from another species - the switch from teleological to transmutationist views. In relation to the struggle for existence, Darwin explains in Origin of Species that "forms that are successful in the struggle for existence are deemed to be slightly better adapted than those with which they have had to compete for their places in the economy of nature".[43] Supporting this claim, in about 1855, Darwin noted that the struggle for existence would produce diversification – leading to Darwin's principle of divergence.[2] Finally, Darwin stresses the fact that the struggle for existence is a metaphor for the larger natural workings rather than the literal struggle between two individual organisms.[44] T.H. Huxley, commonly known as Darwin's Bulldog, clearly explains the struggle for existence in terms of natural selection. Huxley explains that the struggle for existence is concluded based on the fact that populations grow geometrically if unchecked but populations tend to stay constant in number over time.[8]

Alfred Wallace and Darwin independently arrived at the theory of evolution by natural selection.[3] Similar to Darwin, Wallace used Malthus's idea of the struggle for existence to reach this conclusion.[3] In addition, Wallace was influenced by Charles Lyell's Principles of Geology.[45] Lyell discusses a struggle between organisms that causes one species to become extinct; Wallace may have taken the phrase struggle for existence from this example.[45] Additionally, Wallace claimed that it was the collection of chapters 3–12 of the first volume of An Essay on the Principle of Population that helped him develop his theory.[3] "In these chapters are comprised very detailed accounts from all available sources of the various causes which keep down the population of savage and barbarous nations."[46] Then, in 1853, Wallace first used the phrase "struggle for existence" when discussing the issue of slavery.[45] By 1855, Wallace had made connections between the struggle for existence and overall population.[45] Wallace saw in Malthus's writing how there are different ways in which a population can be kept in check:

"From "the law of multiplication in geometrical progression" (the fact that all species have the power to increase their number up to as much as a thousandfold per year) and "the law of limited population" (the fact that the number of living individuals of each species typically remains almost stationary), one deduces that there is a struggle for existence."[47]

Wallace combined the idea of the struggle for existence with variation to argue for the idea of "survival of the fittest."[3]