Introduction The development of the concept of evolution is, in essence, the story of the development of the scientific method. It begins with observation, continues through the development and testing of hypotheses, adds replication, and finally, affirmation of the strength of the theory. The fact that evolution is one of the most-challenged theories in all of science has ended up being one of its strengths. Because so many have sought to reject it, to undermine it, and denigrate it, the theory of evolution has been forced to stand up to all of these challenges. And it has. The reality is that the theory of evolution is one of the most robustly supported theories in the whole of scientific study, and it had to be, in order to withstand these challenges. The constant testing, adaptation and yes, evolution of the theory of evolution over the years has made it the perfect story of the validity of all science.

The Basic Theory of Evolution

Charles Darwin set out his theory of evolution in On the Origin of Species as a means of explaining the differences between species and subspecies of plants and animals. At the outset of the book, he observes that cultivated plants differ significantly from their wild forebears, but also from each other. In other words, apples produced in one geographic region will take on a character of their own, different from apples produced in another region. So different not only from wild applies, but from other cultivated varieties, having adapted over successful generations to the particular conditions in which they live. This basic observation is then extended by Darwin to the natural world, based on his observations there.

He was writing at a time characterized by intense exploration – both of the physical world but also of the natural world, and his work incorporated both of these. He traveled widely collecting specimens and making observations. From this, and his initial observation about cultivated plants, that plants and animals in nature may also derive from an original root species, and if they are segregated by geography or other factors, may end up over time sufficiently different from their forebears. In some cases, the forebear might still exist, while in other cases it may not. But in either case, the animal or plant in question would have developed into a unique species over time, and with sufficient segregation from the forebear species. Thus he observed many relatively common animals in different variants around the world.

He then outlines the theory of natural selection, in particular as distinguished from selection by man. Selection by man is a clear point of differentiation that has helped Darwin formulate his theory. He identifies an observation in a population, and is curious to see if that same phenomena can be observed in another population, in this case one unaffected by man's intervention. Without man to influence the development of the unique species, there are nevertheless unique species that have developed. At this point, Darwin is starting to flesh out the hypothesis on which the theory of natural selection rests. He further observes that for all the mutations that have resulted in different species, there is typically some underlying reason for the change in phenotype – and by extension genotype, of course. The differences between species are result of specific traits being selected over time. If an animal migrates to a colder climate, it grows a thicker coat. If that same animal lives in the desert, it might need a thinner coat, but also better hearing because it may prefer to hunt in the cool of night. These types of observations, taken individually, demonstrate little other than that differences between species exist, and that there is a reason for the differences. What is missing at this point – the point where dozens or hundreds of observations have been made- is any theory to bind the observations together.

That is where natural selection and evolution come into play, because they argue that the observable trait differences in these different species have come about specifically over the course of time, because the defining differences in traits are valuable to the survival of the species within the context of its environment. In other words, nature selects over time for those traits because animals or plants that lack the desired traits survive to reproducing age at a lower rate than those animals or plants that possess the desired traits. The ones that survive at a higher rate to reproducing...

Each animal or plant, therefore, is optimized to survival within the context of that environment.
The final component is that the process is a work in progress. This is what is meant by evolution – the process of evolution in most species is ongoing, or at the very least subject to change if there is a change in the environment. If no change in the environment, a species can exist for a very long time without evolving – most sharks are a good example – but in a changing environment a species either evolves, leaves that environment, or gradually dies out. While we see species in the context of what they are today – a brief moment in time – evolution typically takes place over a much longer period, and is a random, ongoing process, controlled by nothing more than the passing on of successful genes.

Testing the Hypothesis

Darwin laid out the theory of evolution based on natural selection, and immediately the world took notice. He did not perform empirical tests on the theory – it was based on his observations, and logical reasoning that tied that observations together. A theory is nice to have, but proves nothing in and of itself. A theory is really only the second step in this scientific process. Evolution would quickly come under challenge, by those whose power was undermined by the theory's very existence, as they lacked the intelligence to adapt the stories from which they derived their power to the emerging science. These challenges, arguably, created an imperative to test the theory of evolution. Not only was there tremendous curiosity with respect to proving the theory true, just from a scientific point of view, but there was also an imperative to do so, as evolution would prove to be a flashpoint, a cultural battleground, between those who wish to see the world for what it is, and those who fear loss of power should they be demonstrated charlatans.

So it was that the testing of the theory of evolution began. The best test for a theory that covers all life on earth is to find out if it can predict what will happen. Evolution cannot be proven in any single one-off experiment, after all. Natural selection must be the basis for a wide variety of experiments. If its predictions hold true time and again, then this strengthens the evidence for the theory. Ayala (2009) notes that natural selection is the most important component of Darwin's work because it provides the basis for tests today – the underlying principle of natural selection is still part of experiments. This is not to say that longevity is what gives natural selection its power, but the fact that it has been used to successfully predict the outcomes of thousands of different experiments. There are few scientific theories that can claim as many successful predictions as natural selection.

It was more than imperative of course, that has allowed for this. Most theories also do not cover all living beings. It is easy to design thousands or tens of thousands of experiments to test the theory, if given enough scientists and enough time. Natural selection has had both – and it has successfully predicted a statistically valid number of test. Indeed, it has never really failed to predict.

Preponderance of Evidence

A theory requires testing, but then there is the question of how many tests should a theory be subject to before it is accepted as truth. This is where mathematics become involved. There is a point, when measuring different observations, that the weight of those observations takes on verifiable meaning. When enough studies confirm that a theory holds true, versus whatever studies might fail to confirm this, there comes a point when there is statistical validity, that point at which the chance that the theory does not hold true is infinitesimal. The theory of natural selection is well past that point – the preponderance of evidence supports natural selection, and this in turn is the core of the theory of evolution.

Philosophical Thoughts

The philosophy community does not have any particular argument against the core matter of evolution. As Millstein (2017) notes, philosophers tend to accept the scientific method as a robust mechanism for determining truths. This may not have been the case in Darwin's time, but it certainly is today. Further, core concepts such as heritability are accepted.…