Final answer:
The phrase 'survival of the fittest' refers to the relative ability of an organism to survive and produce offspring, where 'fittest' can mean having a range of beneficial traits, not just physical strength.
Step-by-step explanation:
In the phrase 'survival of the fittest,' the term fitness refers to an organism's relative ability to survive and produce fertile offspring compared to others in its population. It is a key concept in evolution by natural selection, meaning that the 'fittest' individuals are those who are most adept at passing on their genetic material to the next generation. Fitness can encompass a wide range of traits, such as behavior, camouflage, speed, or any other characteristic that increases an organism's chances of survival and reproduction. Relative fitness is crucial as it doesn't compare to an absolute scale but rather to the reproductive success of other organisms within the same environment.
For instance, a male bird with bright feathers might be more attractive to mates, thus having a higher fitness value in terms of reproduction compared to a less colorful but physically stronger rival. This dynamic can lead to an increase in the population of offspring with those bright feathers over time if that trait proves advantageous in the birds' environment.
Natural selection acts upon these variations within populations, ensuring traits that confer a survival advantage become more common with each generation. This process is sometimes colloquially and inaccurately equated with the idea of the physically strongest or most aggressive individuals prevailing, but in reality, it is the organisms best suited to their environment and most successful at reproducing that are considered 'fit.'