What is Survival of the Fittest

How often have you heard the term “survival of the fittest” used as an explanation for the theory of evolution? In fact, the term fitness in this context has little to do with physical strength or endurance as one might imagine, and use of the term in this context can be misleading.

In fact the term ‘survival of the fittest’ wasn’t coined by Charles Darwin. Rather, it was a phrase used by Herbert Spencer, an English philosopher who first used the term in his own book ‘Principles of Biology,” although he did so after reading Darwin’s “On the Origin of Species.”

It is a little ironic that Darwin himself began to use the term “survival of the fittest” in place of the original term “natural selection” in later editions of “On the Origin of Species.” This has led to some confusion over the process of evolution as Darwin originally intended it to be understood. It is useful to think of fitness in the context of fit for purpose or usefulness.

This article intends to describe the main points of the theory of natural selection and aims to explain what is meant by the term “survival of the fittest” in this context.

Following extensive travel and study of plants and animals he discovered on his five-year journey around the world from 1831-1836 aboard the Royal Navy survey ship Beagle, Darwin became convinced that all life had a simpler and less-diverse origin than the complexity and diversity seen on his travels. In other words, he had the idea that all life must have come form a common ancestor.

Darwin’s natural selection theory is based on the following assumptions. Collectively, these can be though of as survival of the fittest.

Variation of Species

Any population has a natural variation of traits within the species. In other words, individuals within species have characteristics in either physical appearance or behaviour that is slightly different to other members of the same species. Occasionally, these slight differences can offer some sort of advantage to individuals within a species. For example, a colony of birds may have slightly different beak lengths, some longer than others.

Competition for Resources

Within any given environment, there is a limited availability of resources whether that is food, habitat or anything else that species need to survive. As a result of this, not all members of the species will be able to survive to adulthood or be strong enough to successfully reproduce. Using the example of the birds and beak length, those with longer beaks have the advantage of being able to reach in to deeper crevices to extract the seeds as well as being able to retrieve seeds scattered on the ground. If a situation arises where the seeds are in short supply, maybe as a result of a poor weather, competition from other species for the same seeds or maybe a larger population of the same species following an increase in surviving fledglings that year. In any case, birds with longer beaks able to access the difficult to reach seeds have an advantage. As a result, they are more likely to survive to a reproductive age. Those with shorter beaks are much less likely to reach an age of reproduction. This is natural selection at work.


This is the idea that the variations that exist, such as differing beak lengths have a genetic basis and are passed onto offspring. Since the majority of survivors will have longer beaks, the offspring would also tend to have longer beaks. If the conditions that give rise to long beaks are an advantage, it wouldn’t take more than a few generations for all of the birds within the species to have longer beaks on average.

The same process could equally apply to size or colour or any other variation that might exist. If the conditions favour one trait over another, then the process of natural selection continues. Or as Herbert Spencer and later Charles Darwin himself called it, survival of the fittest.