In evolutionary biology, struggle for existence is a theory which argues that, because food and room are in limited supply, for a living thing to exist, it must struggle. The theory was formulated in 1798 by English demographer and political economist Thomas Malthus; later incorporated by English naturalist Charles Darwin in his 1859 Origin of Species.

Thermodynamics and life

See main: what is life? (theories of existence)

With the development of thermodynamics in the 1850s, scientists, such as William Thomson and Ludwig Boltzman, soon thereafter began to formulate various energetic theories of existence in relation to evolution, life, and entropy.

One the of the major difficulties in the concept of there being a "struggle" in life is that if, according to modern human chemistry, in which, via molecular evolution table logic, biology-sized life and chemical-sized life are supposed to be one and the same, each being differently sized induced movement molecular structures, then it is difficult to conceive of any sort of "struggle" existing in standard chemical reactions, which are very mechanistic. In short, there "is no struggle" between atoms and molecules in basic chemical reactions, so why should there exist a struggle in biology, which are simply larger biological sized reactions. [5]

Overview
In 1798, English demographer and political economist Thomas Malthus published his ‘Essay on Population’, arguing that existence of life is a perpetual struggle for room and food. [1] In short, Malthus outlined the view that population, when unchecked, increases in a geometrical [exponential] rate, but that subsistence increases only in an arithmetic [linear] ratio. Subsequently, according to Malthus, ‘as more individuals of each species are born that can possibly survive … it follows that any being, if it vary ever so slightly in a manner profitable to itself … will have a better chance of survival, and thus be naturally selected.” This meant that, in accordance with Earth’s limited resources, that a ‘struggle for existence’ would emerge. [2]

In opposition to the utopian thinkers of the day, Malthus believed that unless people exercised restraint in the number of children they had, the inevitable shortfall of food in the face of spiraling population growth would doom mankind to a ceaseless struggle for existence. Out of that unforgiving battle, some would survive and many would not, as famine, disease, and war put a ceiling on the growth in population. [3]

In 1838, Darwin, newly back from his voyage on the Beagle and trying to understand the forces that drove the origin of new species, began reading the works of Malthus. [4] Reading Malthus's book (presumably its 6th edition, 1826) triggered in Darwin's mind the idea for a causal mechanism of natural selection. Darwin wrote in his Autobiography (nearly 40 years later), "… [the question] how selection could be applied to organisms living in a state of nature [as opposed to artificial selection, that is] remained for some time a mystery to me. In October, 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population…." [4]

These ideas galvanized Darwin's thinking about the struggles for survival in the wild, where restraint is unknown. Before reading Malthus, Darwin had thought that living things reproduced just enough individuals to keep populations stable. But now he came to realize that, as in human society, populations bred beyond their means, leaving survivors and losers in the effort to exist. [3]

On the logic of Malthus, the general theory that life is a ‘struggle for existence’ is found in the subtitle of Darwin’s Origin of Species , namely that natural selection equates to ‘the preservation of favored races in the struggle for life’, as well as the title of chapter three: ‘Struggle For Existence’. In short, Darwin theorized that: "in the struggle for survival, the fittest win out at the expense of their rivals because they succeed in adapting themselves best to their environment." Moreover, as Darwin stated: "I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection".

In sum, Darwin tended to see species being engaged in a competitive Struggle for Existence. Under the influence of Malthus, Darwin saw this as primarily a struggle for food to support growth, life, and the generation of young individuals to continue the species in question.

References
1. Malthus, Thomas. (1798). On Population, (quote: "the perpetual struggle for room and food", chapter iii. p. 48). Augustus M Kelley Publishers.
2. Moore, Janice and Moore, Randy. (2006). Evolution 101, (pgs. 20-21). Greenwood Publishing Co.
3. Evolution Library: Darwin and Malthus – PBS.
4. Thomson, Keith S. (1998). “1798: Darwin and Malthus”, American Scientist Online, May-June.
5. Thims, Libb. (2007). Human Chemistry (Volume One), (pg. 87, 126). (preview), (Google books). Morrisville, NC: LuLu.