2.3 Darwin, Evolution & Natural Selection

Marcos Antonio de Lima Filho, PhD.

In his classic book, The Structure of Scientific Revolutions, Thomas Kuhn (1962/1996) argued that major advances in science are rare, and that true scientific revolutions involve fundamental changes in how we think. After a revolution occurs, our perception and comprehension of the world are permanently altered. For instance, when astronomers and physicists proved that the Earth was not at the centre of the universe, it led to what Kuhn described as a “paradigm shift”. A similar shift occurred in biology when Darwin put forward his theory of evolution by natural selection (Bergstrom & Dugatkin, 2012). Darwin’s theory of biological evolution is one of the most revolutionary ideas in Western thought, perhaps rivalled only by Newton’s and Einstein’s theories of physics (Futuyma & Kirkpatrick, 2017).

Darwin published On The Origin of Species by Means of Natural Selection in 1859, laying the foundations of modern evolutionary theory. This work is one of history’s most debated scientific developments, and Darwinian evolution is still a work in progress. Though it has been said that evolution by natural selection is a simple idea, today, the subject uses a tremendous amount of data from several speciality areas, carrying with it many interesting implications (Zeigler, 2014). The following literature review focuses on the essential concepts for a basic understanding of evolution and natural selection, emphasising those pertinent to an evolutionary design theory.

The word evolution is derived from the Latin evolvere, which means “to unfold or unroll”, that is, to reveal or manifest hidden potentialities. Today evolution has come to mean, simply, change (Futuyma & Kirkpatrick, 2017, p. 7). Darwin beautifully characterised evolution as “descent with modification”.

Grounded on a series of analogies with artificial selection, Darwin postulated in The Origin of Species a new mechanism of selection directed by nature. Artificial selection, Darwin concluded, was the greatly accelerated analogue to natural selection (Mayr, 1982, p. 486). The first chapters of The Origin discuss well-known examples of selective breeding of domesticated plants and animals. Back then, it was well known that humans had modified other species over many generations by selecting and breeding individuals with desired traits, a process called artificial selection (Urry et al., 2017).

Artificial selection is a millennial practice. Humankind has been selectively breeding grains, such as barley (Hordeum vulgare) and wheat (Triticum), as well as lentils (Lens culinaris) and peas (Pisum sativum), for over 10,000 years (Abbo et al. 2003). The process is straightforward: In the case of crops, in each generation, the best plants — for example, those that are the hardiest, quickest growing, and best tasting — are chosen as the parental stock for the next generation (Bergstrom & Dugatkin, 2012, p. 7). Although artificial selection has been practiced suc­cessfully for thousands of years (for example, with domesticated dogs), only during the last century have the genetic principles underlying its successes become clear (Hartl & Clark, 1997, p. 406).

The logic of The Origin employs one long analogy between artificial and natural selection, with uniformity as the joining point (Gould, 2002). Throughout the book, Darwin frequently refers to examples of artificial selection to support the validity of his inferences. Darwin states in his introduction:

At the commencement of my observations it seemed to me probable that a careful study of domesticated animals and of cultivated plants would offer the best chance of making out this obscure problem. Nor have I been disappointed; in this and in all other perplexing cases I have invariably found that our knowledge, imperfect though it be, of variation under domestication, afforded the best and safest clue (Darwin, 1859/2008, p. 7).

The animal-breeding literature undoubtedly gave Darwin several important insights; by analogy, artificial selection was a splendid experimental confirmation of natural selection (Mayr, 1982). Darwin repeatedly emphasised this parallel and extrapolation: if by artificial selection at a small scale (as we know for sure), why not by natural selection at a larger scale (Gould, 2002).

There is ample evidence that Darwin was a Grounded Theorist ahead of his time (Bryant, 2017). Due to his constant comparisons with artificial selection and inductive approach to facts, many scholars see Darwin as one of the earliest grounded theorists. Darwin writes in his autobiography that he began collecting data “without any theory”, something that could have been taken word-for-word from many Grounded Theory publications (Bryant, 2017).

When Darwin first published his theory of evolution in 1859, the evidence pointing to evolution, including the evolution of man, had been accumulating for decades, and the idea of evolution had been suggested and widely disseminated before (Kuhn, 1962/1996, p. 171). However, unlike his forerunners, Darwin explained design (the harmony of the living world) in a strictly materialistic fashion (Mayr, 1982). His theory of the causality of evolution set him apart from Erasmus, Lamarck, and Chambers, among others.

Until The Origin, the discussions about evolution were conducted on a philosophical basis, stated in metaphysical terms. Darwin was the first author to deal with the subject of evolution strictly scientifically: he supported his thesis with a massive body of facts, and this rich evidence changed the situation quite fundamentally (Mayr, 1982, p. 502). What distinguished Darwin from his contemporaries was his formulation of two major hypotheses: “that organisms have descended, with modification, from common ancestors; and that the chief cause of modification is natural selection acting on hereditary variation” (Futuyma & Kirkpatrick, 2017, p. 8).

Natural selection was, in fact, the great new principle Darwin introduced into biology (Mayr, 1982), which he presented in his seminal work Origin of Species:

As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form (Darwin, 1859/2008, p. 7).

The concept of natural selection is based on differential success in survival and reproduction: Individuals in a population exhibit variations in their heritable traits, and those with traits that are better suited to their environment tend to produce more offspring than those with traits that are not as well suited (Urry et al., 2017, p. 492). The following sections dissect this foundational idea in more detail, reviewing the main patterns of natural selection: disruptive, directional, stabilising, and purifying selection.