How Does Evolution Work? -- A Simple Explanation

Evolution explains how life on earth developed starting billions of years ago, a process that continues to this day. In studying the process of evolution one has to appreciate the massive diversity of living beings on this earth. Evolution explains how very basic protozoa can develop into the millions of varieties of species flourishing among us today.

Evolution answers our questions as we look in bewilderment when seeing a tiny Yorkshire terrier frolicking with a huge Saint Bernard. We wonder how these two vastly different breeds could have the same ancestors. In explaining the answers we’re going to focus on the evolution of animals to the exclusion of other forms of life, like bacteria and plants.

The first question that occurs to us is how does one kind of animal develop into an entirely different species?  First we need to explain what we mean by “species”. A species is a category of animals with a certain kinship that allows them to produce offspring with each other and their offspring are capable of reproducing as well.

To better comprehend this concept we should look more closely at the utter uniqueness of living beings with each one being different than any other. This is guaranteed by the abundant reproduction of offspring with heredity being a factor that we need to examine as well.

Regarding uniqueness, it goes without saying that every living creature is unique. This factor is essential for evolution to take place. The various members of a given species may have a strong resemblance to each other in terms of appearance, however when you examine each one closely you will see slight differences in characteristics and traits. They will vary in size, strength and personality, with some being more aggressive than others.

What causes these differences? When taking a really close look we must recognize that every living being is composed of cells. Each cell has a nucleus containing chromosomes, which hold the DNA. Within the DNA are different genes and these are what carries the information vital to life. Genes contain the instructions the cells must follow and it’s the genes that determine the different characteristics and traits that all living beings have.

Every single creature has its own unique DNA and this is why every living being has slightly different traits and characteristics, even if they are of the same species. The question is how does this huge range of DNA come about? One main factor is through excessive reproduction. In nature it is obvious that animals for the most part continually reproduce and far more offspring are born than is necessary for the species to survive. Many of these offspring actually die an early death due to this practice.

In most cases the number of offspring is more than their environment can support. This one factor explains the increase in diversity within a given species. The more numbers of offspring being born, the more there are differences between them. This is what nature wants, an abundance of all the minute differences within a species as possible.
The second major factor in bringing out the uniqueness of each individual occurs due to heredity. Heredity is the mechanism by which DNA is passed on to offspring. There are two different mechanisms at work here: recombination and mutation.


This is when the DNA of two creatures is randomly mixed together. When two living beings become attracted to each other and mate, their genes are recombined twice. The first time this happens is when the gametes are generated, which are the sperm and egg cells. The gametes shuffle half of the genes. The second recombination happens when the creatures mate and the male inseminates the female with his sperm. Each parent provides 50% of their own DNA, which means half of their own unique characteristics and traits.

The resulting DNA is mixed or recombined and a new offspring is created. All offspring get a random mixture of their parents’ DNA and those determine the characteristics and traits they inherit from their parents. As this goes on the diversity and all the differences within a species increases even more.


Mutations occur randomly and change the DNA, which make mutations very important in the process of evolution. They are errors in copying within DNA and come about due to environmental toxins, chemical substances, or possibly exposure to radiation. If a part of the DNA is changed or altered in any way, a mutation occurs. Oftentimes the change that happens is negative and can lead to certain illnesses, maybe even cancer.

However the mutation may even have a neutral or possibly a positive effect. One such positive effect is the blue coloration in the eyes of humans, which resulted from a random mutation.

No matter what the result, a mutation affects a gamete, a sperm or egg cell. Since only the DNA contained in the gametes is inherited by the offspring, we must shield our sexual organs when having an X-ray. To summarize, through the process of heredity all living beings pass their characteristics and traits on to their offspring using their DNA.


Through the processes of recombination and mutation, the DNA is changed, which means that each child has a different appearance than their siblings and each child receives a random mix of traits and characteristics belonging to his or her parents.

The key to all of this is the random nature of these processes. It is all a matter of chance. Random recombination along with random mutations brings about offspring each having a random mix of characteristics and traits. Each individual offspring then randomly mixes things and passes them on. One has to ask, if so much is left to chance, all living beings are so well adapted to their surroundings and environment at large?


The answer to the question is fundamental to the survival of a species, natural selection. Each individual creature is subjected to the challenges posed by their environment. In order to survive they must pass through a natural process of selection. We realize that each creature within a species is fundamentally the same but there are large variations.

These variations are the result of environmental factors and the effect they have on the creatures living there. These are called selection factors and they include animals from the same species, changes in climate or habitat, parasites and/or predators.

Since each creature has its own unique combination of characteristics and traits these can help them survive the challenges of their environment, or not. Any creature with a mix of traits and characteristics that make them unsuited for their environment, will be selected out and not survive. Those with the types of traits and characteristics suited to the environment in which they are living, will survive and be able to pass on their stronger traits and characteristics to their offspring.

This is why having diversity is so vital. This is the reason why living beings go to such an effort in producing offspring as different from themselves as possible. They instinctively know that by doing this they increase the chances of at least one offspring passing through the natural selection process, and surviving to creature future offspring or generations.

An interesting example of this process of natural selection can be observed in a community of finches that live on a remote island. These finches are extremely famous scientifically, being referred to as “Darwin finches” after Charles Darwin discovered and studied them. This is their story.

The Darwin Finches

Several hundred years ago a small band of finches were blown afar by a big storm landing them on the Galapagos Islands, which are in the middle of the Pacific. These little birds wound up in a totally unfamiliar environment and happily so. This was paradise for them with plenty of food and not a single predator. As a result they rapidly reproduced in large numbers. Soon the Galapagos Islands were overloaded with finches, compromising food supplies. As food became more and more scares, what once was a paradise for them became threatened with starvation and the other finches became competitors for food.

The process of selection intervened at this point in time. Their individual differences helped them survive. Small differences in their beaks helped some birds avoid competing for food. Some had beaks that worked well digging for worms. Other finches had beaks suited for cracking seeds open.

The finches were smart and looked for ecological niches where they were protected from too much competition. They then began mating with other finches that existed in the same area, having the same kind of beak. Over many future generations this characteristic beak became enhanced, helping this breed of finches survive by exploiting their own niche successfully.


Eventually the differences between the finches who were seed crackers and the ones who were worm diggers became so large they no longer could mate with each other. As a result two different species of birds emerged. On the Galapagos Islands today there exists a total of fourteen different species of finches. Each species descended from the same band of finches. This is how a new species comes about by way of evolution. Through various steps in the process, which starts with the interacting of unique individuals in a given species mating and producing an excessive number of offspring.  Recombination and mutation brings about different characteristics and traits through heredity. And finally through a process of natural selection, different species evolve.

The process of evolution informs us where all the varieties in living beings come from. Evolution explains why all living beings seem so well adapted to their surroundings and habitats. Evolution also has an effect on us personally. Every individual person on this earth has resulted from a period of evolution lasting three and a half billion years. This includes you. Every one of our ancestors fought hard to adapt so they could survive.

There was no guarantee they would survive. The fact is that 99% of all the different species that have lived on this earth are now extinct, you can appreciate that your existence is due to a success story. Although dinosaurs are extinct you are not and are able to sit here and watch this video. You can consider yourself special, just like all the other living beings that have survived and are populating the earth today. Every one of them and us are unique and irreproducible anywhere on earth or in the universe.

If you like our posts, subscribe to the Atheist Republic newsletter to get exclusive content delivered weekly to your inbox. Also, get the book "Why There is No God" for free.

Click Here to Subscribe

Donating = Loving

Heart Icon

Bringing you atheist articles and building active godless communities takes hundreds of hours and resources each month. If you find any joy or stimulation at Atheist Republic, please consider becoming a Supporting Member with a recurring monthly donation of your choosing, between a cup of tea and a good dinner.

Or make a one-time donation in any amount.