That’s perhaps not a question you’ve asked yourself, but like so many things we take for granted, it is worth taking a step back and thinking about.
That’s why my first post is dedicated to this simple question. As will be the second, because there’s too much to explore for a single post.
First this first part, a bit of travel back in time is on the menu.
In the somewhat strict biological sense, fitness is the ability to exist, survive, and reproduce, in a given ecological niche. (I’m paraphrasing, of course, since I’m not a biologist.) In essence, the individual “fits” with the conditions and environment that prevail at that time. So:
Fitness = Adapted to one’s environment
More often than not, biological fitness is measured by the transfer of genes from one generation to the next. This “success” at reproduction is what leads to the notion of survival of the fittest. It does not mean the individual has beaten up all competitors (that may happen as well, but not as often as popularly believed); it is a simple indication that the individual has given rise to a sizable portion of the next generation. Thus:
Fitness = Reproductive Success
We’ve come some way from our origins as struggling animals. We’ve distanced ourselves from the hardships of the environment through clothes, fire, housing, agriculture, machines of all kinds, etc. Some might argue we’ve completely detached ourselves from the grips of evolution. They’d be wrong, of course; we’ve only changed our environment, modified it much faster than we’ve modified ourselves through natural (or otherwise) selection.
In that respect, our reproductive success is amazing, but our bodies may no longer fit the environments in which they now live. This leads to lots of health problems. Those among us who are overweight are only the most visible aspect, a symptom really, of this. (Careful: overweight does not necessarily mean unfit. The correlation with many health issues, however, is undeniable.)
I would go as far as to say that our current way of life makes us all unfit to a great extent. We have facilitated our lives to the point of taking cars everywhere instead of walking, taking escalators and elevators instead of stairs (yes, I’m aware there were no stairs in the African Savannah, but bear with me), eating our fill pretty much every single day (for a large portion of the population, pun intended), etc.
Our bodies are not prepared for that, and it will take time for evolution to compensate. But I don’t think we should let evolution take its course in this case. It would simply take too long, and too many would suffer needlessly in the process.
That’s why those definitions are not entirely satisfactory anymore. The first one still has value, as we’ll see later, but it demands that we consider a bit more what our environment has become.
As to the second definition, I think we should reject it altogether. We have developed technologies that compensate for nature in guaranteeing reproductive success. At any rate, overpopulation and the footprint of humanity on our only planet are already problems that demand a lot of attention. Let’s not focus on adding more of us as a measure of success.
So we must look elsewhere for a current, useful, definition of fitness.
That’s what I’ll continue doing in the second post on this topic.