The meaning of fitness

           The notion of fitness has undergone different interpretations and alterations as to its definition.
If you a believer of the origin of species, well even if you are not, the idea of fitness was understood as an element of survuval and mating. In the animal world today and even millions years ago , animals who showed fitness were able to survive and even ward off pradators,and more importantly were able to win a mate for reproduction. Female had the power to select the male that is fit and would pass on the good gene to the offspring. Unforntunately or maybe fortunately, depends on where you find yourself in the category, the same reality applies today in the human species and even more so.
            But the idea of fitness wasn't limited only on the physical aspect, as having six packs and all , but it characterized also different aspects of life. A male who were able to bring food to a female was considered by her as being fit, or being able to protect her was an impressive quality in the fit male.
Now the physical quality was such that it was the first factor of attraction, notably the girafe with the longest neck was and is imposing therefore fit, the lizard who could perfom more push ups was the "man".
            Today the definition of fitness has taken a more biological approach while preserving some elements if not all of its primitive meaning. The physical characteristic of fitness still very much a factor of consideration in the mating( relationship) department. The females still have the power to chose the male they think fit. There has been a nuance of reciprocity that males also pick females without any abstraction of fitness a priori.
          The scientific aspect, more precisely the biological aspect of fitness, in human's view, has to do with the wellness of the body. Is fit someone who benefits a well functioning of the body due to some physical activities(exercise) or a proper nutritional value intake.
 In regard to the different elements of the definition of fitness, it has become a culture that has evolved . Through time and space it has evolutionarily lost or gained some elements.
At the end of the day it is only beneficial to human.
So stay fit.