Assessing Modern Evolutionary Theory

Explaining Modern Evolutionary Theory

Most people have heard of Charles Darwin, the nineteenth century English scientist and author of On the Origin of Species, which he published in 1859. This work presented the idea of natural selection and deeply challenged the current thinking of human origins. Speaking of the impact of the variation present in species over time, Darwin defines natural selection: "This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called Natural Selection, or the Survival of the Fittest."¹ In other words, he theorized that because organisms change over time from generation to generation, then slowly, over several generations, those individuals in a given species that are the "fittest" or best equipped to survive and reproduce, will disproportionately contribute to the next generation, leading the species to become more fit to their environment over time. Since his book's publishing, biologists and other scientists have continued to build upon his theory, forming what today is called modern evolutionary theory.

Modern evolutionary theory claims that all life on earth originated from one life form that gradually evolved over time being driven by natural selection, and creating new species over the last 3.5 billion years. The theory consists of six ideas:

• Evolution - species change genetically over time
• Gradualism - significant change takes many generations
• Speciation - the evolution of different groups that can't interbreed
• Common ancestry - every pair of species shares a common ancestor sometime in the past
• Natural selection - population will gradually become more and more suited to its environment as helpful mutations spread through the population
• Nonselective mechanisms - random changes that don't impact survival can also spread through a population²

Contrary to a creationist view that all creatures were created as they are now relatively recently, modern evolutionary theory implies that humans descended from primates (monkeys) and that mammals descended from reptiles, which themselves had descended from fish.

Whether or not modern evolutionary theory is true or not has major implications for our understanding of our origins, our nature and our purpose. Here are just a few:

• Religions based on a creationist understanding of our origins may find evolution as largely, but not completely, incompatible with their respective faiths. Religious belief has been a significant source of the skepticism of evolution since Darwin proposed the idea and remains a major source of opposition to the idea today. Many find the idea that we may be the products of a somewhat random process of natural selection, rather than a special object of creation, unsettling.
• Accepting evolution would imply that we are very related with all the other animals and plants on the planet. This idea challenges our deep psychological intuition, and common religious claim, that we are fundamentally different from other organisms and that we have a special place in the cosmos.³
• Many of the moral codes worldwide are rooted in an understanding that humans have a specific, created purpose on Earth. Evolution doesn't necessarily negate morality but challenges the basis upon which mortality has traditionally rested.

Exploring Previous Thought

The first records we have of the concepts of evolution and natural selection are in ancient Greece and Rome. Anaximander was a Greek philosopher from Miletus who theorized, in the sixth century BC, that humans must have arisen from other animals and were related to fish.⁴ Lucretius, a Roman poet from the first century BC, describes in his work, On the Nature of Things, an idea very similar to natural selection. He argued that species not possessing some special quality would not be able to survive or reproduce, ultimately dying out.⁵

Although many had proposed evolutionary concepts before, Charles Darwin was able to piece together different types of evidence in support of a theory of natural selection that was eventually compelling for the scientific community, even though it faced strong opposition from religious figures.

As mentioned above, the theory of evolution assumes that species change over time as a result of mutations. DNA (deoxyribonucleic acid) is a string of molecules containing the instructions to create the right combination of proteins for a specific organism. The mutations are errors in the copying of DNA, causing the next generation to be slightly different from the preceding one. If a mutation causes an enhancement to an organism, such that it is more likely to survive and/or become better at producing offspring, then that gene (piece of DNA code) will spread more, on average, to the next generation than other competing genes.⁶

This theory makes several testable predictions about life on earth, including:

• Evidence of evolutionary change in the fossil record
• Transitional species, or "missing links", between major groups
• Imperfect adaption, as a opposed to conscious design⁷

Evidence has seemed to surface for each of these predictions:

• The oldest fossils found are for the simplest organisms from roughly 3.5 billion year ago and they become more complex with time. There is a clear progression in the fossil record of fish first, then amphibians, then reptiles, then birds and mammals.⁸
• A notable discovery of a possible transitional species between fish and amphibians was made in 2004 of the fossil species tiktaalik roseae. It had both fishlike and amphibian-like features suggesting that it lived in shallow water but could probably breathe above the surface.⁹
• Several species have vestiges, or features that were an adaption for its ancestors but no longer useful in their original way. This is is a sign of imperfect adaption, as perfect design would not need to reuse old features.¹⁰

Defenders of a creationist world view have argued that evolution cannot explain everything in biology, often using complex adaptions like the eye as a key example. This is commonly referred to the "God of the gaps" argument. However, as science continues to advance, it seems there is a smaller and smaller gap and this is true in evolutionary biology as well. Astronomer Carl Sagan pointed out that evolution can be hard to understand because of our inability to fully appreciate how much time was available for evolution and how much change can happen over billions of years.¹¹

Evolution has more difficulty in explaining the mystery of how life began in the first place. From an evolutionary point of view, life is thought to have arose from a primeval soup of chemicals on the surface of a young Earth. Given enough time, it's possible that UV light from the sun could cause organic substances to form in the soup, eventually leading to self-replicating molecules.¹² Until this process can be replicated or more compelling evidence gathered, answers to this question are limited to the realm of speculation.

Another phenomenon that evolution, as well as science in general, has had trouble explaining is consciousness. The "hard problem of consciousness" describes the difficulty in explaining how physical brain processes give rise to subjective experience. This problem is "hard" because it is difficult to obtain objective data for the one thing that is fundamentally subjective: consciousness. Proponents of evolution would argue consciousness emerged as a mode of sharply focused attention that combined sensations, emotions, and thought together in subjective experience.¹³ It's our brain's way of generating an internal reality or model of the world based on clues from the outside world, such as light waves and changes in air pressure.¹⁴ While this may explain why there is consciousness, it doesn't seem to explain exactly how it works.

Employing Method

We have much data to assess modern evolutionary theory empirically, and some examples were already mentioned. A highly compelling argument for evolution is how well data from so many different scientific disciplines fits together. Cross-correlating strata from around the world provides a comprehensive order of sediment layers and allows us to see the order of life over time. Additionally, radioisotope decay allows geologists to estimate the age of different rock layers, providing not only ordering but timing as well. These ages are confirmed by other sources of data like the rings on ancient coral.¹⁵ The type of life we see over time is also consistent with what we would expect based on changes in the oxygen and carbon dioxide levels in the atmosphere and the timing of warm and cool temperature cycles.¹⁶

We can look at the primary mechanism for evolutionary change, natural selection, from a logical perspective. The key to understanding natural selection is to focus on the survival of the gene, not the creature, because it is the gene that carries the genetic instructions for the organism that carries it and it is the gene that can be passed on to future generations. Genes are not conscious, but we can speak of them as being selfish, in that they want to survive and multiply - if they were not "selfish", they would not survive to the next generation. Genes that are advantageous to their organism will help it survive at least long enough to reproduce.¹⁷ The logic behind the theory of natural selection is internally consistent and the results of evolution appear significantly more plausible when considering the immense amount of time, billions of years, for the mechanism to operate.

When looking at nature through an evolutionary lens some observations start to make sense intuitively. One observation is that all vertebrates, which include fish, amphibians, reptiles, birds and mammals, have four limbs. This makes sense if they are all related genetically and stemmed from the same ancestor. While it's certainly possible that an intelligent designer could have just made them this way, it seems an odd self-imposed limitation for all vertebrates to have four limbs as opposed to some having six or eight. Another observation is that some people have a feature where their ears can twitch slightly, either voluntarily or in response to sound from a different direction. This has no practical function today but makes sense only as a vestigial feature from an ancestor that needed it. In other words, there is no reason an intelligent designer would have included the feature in humans, but the feature is perfectly explained by evolution. One other observation is aquatic mammals like whales. If an intelligent designer wanted to keep groups of animals "nice and tidy", it could have been the case that all aquatic vertebrates were fish, but they aren't. Whales are closer genetically to species of land mammals than fish, and there is significant evidence in the fossil record of transitional species from artiodactyls (group of mammals including camels and pigs).¹⁸

Modern evolutionary theory is very compelling because of not only the extensive evidence in the fossil record and genetics, but also the consistency between all the different types of data. Most predictions of the theory have been confirmed with subsequent discoveries. The theory makes sense logically, and once understood has a significant intuitive appeal. Based on the evidence, logic and internal coherence, I find it virtually certain (>99%) to be true. I think the theory has more and more explanatory power as it is applied in more scientific domains, like psychology and psychiatry. However, it is not apparent to me that the theory of evolution and the concept of God are mutually exclusive. It is not hard to imagine God creating the universe and setting in motion the forces that would create an environment that life could thrive.

¹Charles Darwin, The Origin of Species: By Means of Natural Selection, in Great Books of the Western World, vol. 49, ed. Mortimer J. Adler (Chicago: Encyclopaedia Britannica, 1952), 40.

²Jerry A. Coyne, Why Evolution Is True (New York, NY: Penguin Group, 2009), 2.

³Carl Sagan, The Varieties of Scientific Experience: A Personal View of the Search for God (New York, NY: Penguin Books, 2007), 39-40.

⁴James Evans, "Anaximander," Encyclopædia Britannica, last modified February 13, 2024, accessed January 4, 2026, https://www.britannica.com/biography/Anaximander.

⁵Lucretius, Lucretius: On the Nature of Things, in Great Books of the Western World, vol. 12, ed. Mortimer J. Adler, trans. H. A. J. Munro (Chicago: Encyclopaedia Britannica, 1952), 72.

⁶Richard Dawkins, The Selfish Gene, 4th ed. (Oxford, UK: Oxford Landmark Science, 2016), 21-22.

⁷Coyne, 17.

⁸Coyne, 28.

⁹Coyne, 35-37.

¹⁰Coyne, 56.

¹¹Sagan, 64-65.

¹²Dawkins, 18-20.

¹³David Christian, Origin Story: A Big History of Everything (New York, NY: Little, Brown Spark, 2018), 145.

¹⁴Will Storr, The Science of Storytelling (London, UK: William Collins, 2019), 21-22.

¹⁵Coyne, 22-23.

¹⁶Christian, 139-141.

¹⁷Dawkins, 29-30

¹⁸Coyne, 48.