As humans, we look around ourselves and marvel upon how the endless forms of organisms we see, and the ones we are yet to discover, have come to be. How the spectrum of life arose and became interconnected. What’s more, how to classify them based on similarities and differences in some hierarchical form. That’s a challenge that Carl Linnaeus grappled with his entire life in the 18th Century. It wasn’t until Darwin that there was any kind of mechanism that explained the divisions between Linnaeus’ classifications of Domain, Kingdom, Order, Family, Genus and Species. However, Darwin and Linnaeus’ breakthroughs hinged on a number of paradigm shifts in thinking, provided by their scientific contemporaries.
- Methodological Naturalism was an early step in what is now the philosophy of science, precluding the ‘supernatural’ as an explanatory cause for the natural world.
- Aristotle’s shift from the acceptance of a priori (purely logic-based) knowledge, to the quest for a posteriori evidence-based reasoning, involving observation,
testing and refutation of hypotheses.
- Uniformitarianism, the key concept that natural laws and processes have been operating continuously for millions of years, forming geological structures such as rivers, mountains and ultimately the evolution of all species.
Darwin’s insights corrected two deficiencies in Aristotle’s Scala Natura, which postulated: a chain of being of increasing complexity, as opposed to the accepted idea of an interconnected web of nature, and the false notion that that the chain was and always had been fixed in its composition, in ignorance of the ever-permeating flux of life. This also implied that no other species that wasn’t alive at that point had ever been alive previously, opposing the concept of extinction. Although not extensively covered in Darwin’s On the Origin of Species, extinction is a vital concept in the study of Evolution, setting into motion the notion that species better suited to an environment had peferential survival and reproductive success in passing on their genetic information, while others that weren’t would perish.
Darwin tackled this theory in a way that would appeal to his audience in 19th Century England; pigeon breeding. He used this example to exhibit how selection, albeit in an artificial manner, could manifest itself in the physical transformation of descendants over a relatively short period of time. A similar, yet subtly different method of displaying this change is through experimental evolution, a technique where a selective pressure is applied (change in environmental temperature) is applied to a population (ie. E. coli) to promote evolution, as opposed to physically picking out members with the desired trait – more on this later. The selective pressure has also been termed the Struggle for Existence by Thomas Malthus.
Metaphorically speaking, selective pressure is also conveyed as a sieve, or a variational process, where a population with different values for a specific property (ie. size, quality or fitness) are separated from each other based on the property. A common example is the interview process, where the course of the interview is the selective pressure, the interviewee’s intelligence under duress the differential property and the interviewer striking out your name the agent of death. Opposingly, a transformational process would involve interviewers taking a random cohort of graduate students and teaching them the ins and outs of the job until they reached a level of proficiency acceptable for the company.
Sticking with this frame of thinking, Darwin’s most powerful metaphor was his Tree of Life, spawning the creation of phylogenetic tree diagrams that show inferred historical evolutionary relationships based on similarities and differences in physical, behavioural or (now) genetic characteristics. In his metaphor, budding twigs represented extant species. The tree’s original trunks have now flourished into thousands of branches, fighting against each other for sunlight. Some branches were not able to procure sufficient resources, and have since decayed and dropped off due to the buffeting of the wind.
Naturally never without criticism, refutations against Darwin’s theory included evolution’s seemingly impossible task of designing intricate and complex structure such as the eye and the brain, the presence of vestigial traits and body parts that seem to now be of little importance, and the maintenance of phenotype variation in the face of natural selection.