Natural Selection: Survival of the Fittest

Most people in the western world used to have a solid idea about our origins: all living organisms were deliberately formed by a single creator. Then, in 1831, a 22-year old student decided to go on an expedition that would change everything. Upon returning home Darwin came up with his theory of natural selection — a process through which living organisms adapt, reproduce, and change. The evolution of peppered moths in the United Kingdom during the industrial revolution is a great example of this process.

the true story

In the beginning of the 19th century, most people in the western world had a solid theory about our origins: all creatures were formed by a single creator. 

But then, in 1831, a 22-year old student decided to go on an expedition that would change everything. The young man spent years on remote islands, investigating living organisms and taking careful notes on their differences.

After close to five long years, the man returned home. He organized his findings, and started to write his own theory on the origin of species. Decades later, in 1859, Charles Darwin, supported by the work of Alfred Wallace, challenged the status quo with his theory of evolution – based on natural selection.

Natural selection theory
Natural selection theory

Natural selection is the process through which populations of living organisms adapt, reproduce, and change.  This is possible because organisms evolve when random mutations happen in the DNA of reproductive cells. 

Stored in cells the DNA contains instructions that determine an organism’s characteristics early after conception. For instance, two animals with particular features, can have a baby with very special ones.

Competition for limited resources

Since most of us are in competition for limited resources, territory, or potential partners, certain traits are beneficial, while others are not. And when the survival of one is challenged by the presence of another, some can get by as they are, while others must adapt or they will die out.

One way to adapt is to specialize for particular ecological niches in order to survive and reproduce. Over time, it may be that there are certain mutations that later happen to improve one’s ability for reproduction.

If these particular traits are also heritable, that is, passed from parent to offspring, then there will be a reproductive advantage – and that’s what modern evolutionary theory defines as fitness.

survival of the fittest
Survival of the fittest

The phrase “survival of the fittest” stands for the process within a population, where fit variants leave reproductive copies of themselves and less fit variants reproduce less or disappear.

Over generations, fit traits become the dominant variation in a population and can eventually emerge as a new species – a group of similar organisms who interbreed with each other – and no others.

And as all of this happens in the surroundings of the organism, which may change any time, it’s their natural environment that “selects for” how successful a species is at reproduction. And this is why the entire process is known as natural selection.

real life example
peppered moths example

One famous real life example is the story of peppered moths, which populated the United Kingdom with the perfect texture to blend into their natural environment.

In the 1800s, the industrial revolution then changed that. Factories and homes darkened the skies and the smoke from coal blackened everything. Over time the tree barks also became darker, and white moths were more visible to predators, while the less prevalent black moths became invisible.  As a result, peppered moths were more likely to be eaten and dark ones ended up having a reproductive advantage. 

By 1970, in some regions almost all moths had dark wings. They were not stronger, not faster, not smarter, but simply fitter. As humans started paying attention to the environment, this tendency reversed. Today mostly white moths dominate in the UK again.

Random genetic mutations were giving dark moths a reproductive advantage in a certain environment for a certain period of time. 

what do you think?
What do you think

What are your thoughts? Are all species related? And if so, do all stem from the same single origin? And if that’s the case, how do we solve the chicken and egg problem? Share your thoughts in the comments below!


Dig deeper!

Classroom activity

In the following activity students will learn something about natural selection in an unnatural environment.

  • Present to the students a photo of a wolf, and a photo of a chihuahua.
  • Put them in teams of two or three, and ask them: If they have a bunch of wolves, and want a chihuahua, how would they go to create one?
  • After 10 minutes, collect their answers.
  • Show them Sprouts video on natural selection.
  • Ask the students if they want to keep their answer or if they want to come up with a new one.
  • Resolve the answer and explain that small wolves should be selected and made to reproduce, the same should be done with their offspring, and so on. This selective breeding program will over time create small canines much like chihuahuas.
  • Once you are done and you have time left, ask the class to come up with some of the problems and ethics challenges of selective breeding — especially when done with humans, such as it was tried during Nazi Germany.


  • Script: Jonas Koblin
  • Artist: Pascal Gaggelli
  • Voice: Matt Abbott
  • Coloring: Nalin
  • Editing: Peera Lertsukittipongsa
  • Production: Selina Bador
  • Sound Design: Miguel Ojeda
  • Fact Checking: Ludovico Saint Amour di Chanaz

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