The fitness according to Darwin, refers ultimately to reproductive fitness. Explain.

Explanation

Any population has built in variations in characteristics. Those characters which enable some organisms to survive better in natural conditions (climate, food, physical factors, etc.) would outbreed others, which do not possess such characteristics to survive under such natural conditions. Thus, fitness of an individual refers to reproductive fitness. Hence, those who are better fit in a environment, leaves more progeny than others. These, therefore, will survive more and hence selected by nature i.e. natural selection/ mechanism of evolution.