Within much of western science prior to the 6^th century BC, creation myths pervaded much of the answers to the creation of the universe and the species within it.

Aristotle had proposed a taxonomy of nature. Amongst the Ancient Greeks, Empedocles had proposed an early form of spontaneous generation, where individuals were assembled from parts that, if unable to function together, became extinct, while Aristotle detailed the diversity of life in his Great Chain of Being, in which all species existed on a fixed landscape in which one would eventually become the next, with humanity positioned at it’s peak.

Most of our understand of the history evolutionary biology comes from these thoughts which encompassed much of the discourse for the next 2000 years. It wasn’t until the mid-1700s that George-Louis Leclerc and George Hutton, inspired by new thoughts on the vastness of the cosmos made clear by the invention of the telescope, began to seek new ways to measure the history of our planet. Through geological and fossil evidence, they argued that the world was inconceivably old i.e. in the millions if not billions of years, and certainly much older than the 4000 years posited by the church at the time.

This search for the age of the earth led geologist Charles Lyell to propose that the geological features present today are driven by the same processes that we see around us, but over very long periods of time. We know these ideas were fundamental to Darwin’s theory of evolution as he wrote multiple books drawing from Lyell’s work. In fact, much of Darwin’s theory can be attributed as biological interpretations of Lyell’s work.

 

 

At the same time as this search for the timescale of earth’s biological process, scientists were studying the origin of the diversity of species they saw around them. In the mid-1600s, challenged the oft-held notion of the time that organisms came spontaneously from objects in the world around him. Francesco Redi showed his contemporaries that flies did not spontaneously arise from rotting meat, but rather than they emerged from the larvae of flies that had come to feed on the meat previously.

A few decades later, Erasmus Darwin, grandfather of Charles Darwin, first proposed the ideas of evolutionary change in his book Zoonomia. He described a constant struggle for existence, where species had to fight for resources to produce more offspring than those around them.

Shortly after, geologist Robert Chambers stated that the composition of species has slowly changed over evolutionary time and that, more importantly, these processes act on populations as opposed to individuals themselves. This led to his Principle of Progressive Development, where he hypothesized that new diversity and species sprung from previous generations.

 

 

While we can more clearly see the early formations of evolutionary thinking in these works, what scientists of the time lacked was a strong explanatory link between evolution, species, and the environment.

In the early 1800s, theologian William Paley introduced the idea of the watchmaker – stating that the complexity of each species was similar to the complexity seen in the mechanisms of a clock and could not have arisen through chance. Just as each mechanism within a clock is expertly crafted by a watchmaker, so too is each species crafted by a creator.

At the same time, Jean-Baptiste Lamarck, in his book Zoological Philosophy, rejected this idea and argued that it was the passing down of traits gained during the lifetime of an individual from one generation to the next that led to the match between environment and organisms.

 

 

Toward the mid-1800s, Scottish writer Patrick Matthew proposed the circumstance-adaptive law which stated that since resources are limited, only a certain number of offspring could survive to the age of reproduction, and so individuals that differ in terms of their traits could gather these resources better and lead to organisms that are well-adapted to their environment. This close similarity with Charles Darwin’s work led to Matthew being mentioned in the 6^th edition of the Origin of Species. However, while Matthew did note the process of natural selection, Darwin had two additional components to his work that led to it’s widespread usage: the concept of common descent and over 20 years of scientifically-driven supporting evidence.

Before Darwin, evolution was seen as a transformation process, like that which was proposed by Lamarck, in that all things that existed before still exist in some form today. Darwin’s work challenged this line of thinking, arguing that it was a variational process. Drawing on the ideas of Thomas Malthus, a political economist and contemporary of his grandfather who showed that human population, unless kept in check by war, famine, and disease, grows at a rate faster than the availability of resources, Darwin stated that many species that existed in the past no longer exist today in any form. Only those species that made it through the environmental and evolutionary sieve are the ones that we see in the present-day.

 

 

Darwin, along with his colleague Alfred Russel Wallace, expanded on this to develop a more complete theory of evolution, joint publishing their respective findings in a publication to the Linnaean Society. The main addition to this work was the concept of the hierarchical relationship of organisms, tied into Darwin’s concept of descent with modification, as the explanation behind how variation of organisms could lead to the development of new species. This work also explained the common patterns that exist in nature, allowing similarly related species to be clustered together based on common ancestry and leading to the field of study known as systematics.

Darwin and Wallace’s work also noted the similarities between the patterns of geography with the patterns of speciation, describing the roles of geographic barriers in influencing more dissimilar species forming. This opened the theory of evolution to be applied to organisms at much smaller scales, as geographical barriers are dependent upon the scale of the organisms themselves. However, while they had moved across space-based scales, the scientists underestimated the scale at which evolution could occur. We know now that evolutionary change can be witnessed and studied within much shorter time-scales than those Wallace and Darwin had originally thought it could be.

The theory of evolution wasn’t without it’s problems at first. Critics of Darwin and Wallace’s theory stated that if natural selection favoured traits that have a present-day value, then intermediate traits couldn’t have formed as they would hold no value. In addition, the asked how traits that lacked any apparent biological function could persist. Lastly, many contemporary scientist argued that if the action of natural selection reduces variation, then evolution should just stop. It is important to note that sll of these were studied more in-depth as time went on, many leading to entire new sub-fields within the field of evolutionary biology.