Summary
An organism's relative contribution of offspring to the next generation.
In depth
Darwinian fitness is lifetime reproductive success, including survival to reproduce, mating success and fecundity. Inclusive fitness also counts effects on relatives. Fitness is context-dependent and measured relative to others.
Common mistake: fitness is not physical strength.
Components include viability (survival), mating success and fecundity, and generation time also matters. Absolute fitness is the number of offspring per individual, relative fitness is compared with the average, and selection depends on relative differences. A selection coefficient measures the disadvantage. Fitness can only be measured in a given environment, and also depends on frequency of other types.
A heavily built animal that lives a long time but leaves no offspring has zero fitness. Frequency-dependent selection, in which rare types do better, maintains polymorphisms, as in the colour morphs of side-blotched lizards that play rock-paper-scissors.
Common mistake: reading fitness as physical strength; it is about reproductive success.
Frequently asked questions
What is Fitness?
An organism's relative contribution of offspring to the next generation.
Which area of biology covers Fitness, and how advanced is it?
Fitness is one of the 53 topics in Evolution. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Evolutionary Stable Strategy, Natural Selection, Evolution.
Can you give an example of Fitness?
An organism that is small but produces many surviving offspring is fitter than a large one that produces few.
What should I learn before Fitness?
Work through the Beginner topics in Evolution first, such as Evolution, Natural Selection, Charles Darwin, then return to Fitness. Intermediate topics assume the Beginner vocabulary.
What topics are related to Fitness?
The closest topics to Fitness are Evolutionary Stable Strategy, Natural Selection, Evolution, Sympatric Speciation. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Fitness?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Fitness. To practise the whole of Evolution, use the Evolution quiz.
How is Fitness different from Evolutionary Stable Strategy?
Fitness: An organism's relative contribution of offspring to the next generation. Evolutionary Stable Strategy: A strategy that, once common in a population, cannot be invaded by any rare alternative. Read both side by side and note what each one explains.
What is a common mistake about Fitness?
Fitness is not physical strength.
How should I study Fitness step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Evolutionary Stable Strategy and explain the difference aloud. Finally, take the Evolution quiz and come back to this page for any question you miss.