Because it takes the observation of Survival and uses it to infer Fitness, at the same time as saying that Fitness confers Survival.
That's a function of the explanation being an extremely good explanation. It rises to the top precisely because it has explanatory power all across nature without evident counter-example.
>There is no configuration of organism that would cause you to say "huh, I guess Survival doesn't depend on Fitness after all!"
This is where the argument falls apart. For starters, species go extinct all the time for reasons tied to their evolutionary trajectory. And there are species still living that unfortunately seem very imperfectly adapted to their constraints and likely to go extinct without a run of good luck or human intervention (e.g. pandas). We seem perfectly capable of recognizing when such species are "on the ropes". Additionally there are relative advantages we can clearly observe from animals in overlapping niches, and we can marvel at the effectiveness of adaptations in ways that don't involve circular assumptions (e.g. algae's capability for efficient growth is astonishing and without equal on the planet).
And, we could surely conceive of preposterous examples that defy expectations (e.g. the other commenter's example of mice with 100ft teeth).
It probably feels like it proves too much, because it's confirmed over and over again in nature everywhere, at all times. But in an alternate world where that wasn't the case, counter-examples would abound (such as the mouse with 100ft teeth). So re-iterating the core lesson about the role of natural selection is not just a circular assumption, it's the culmination of hard earned, accumulated evidence, ready at any moment to be falsified.
The honeybee is a perfect example, because the stinger does pose a real question about how we understand it's relation to fitness, and it requires delving into all kinds of complicated dynamics about genetically related drones are to the queen, the role of the sacrifice in supporting the hive and so-on. If we didn't have explanations like those, it would indeed pose a problem with explanations that presume fitness.
That's a real payoff from being alert to the need to have robust explanations; I don't think anyone is just saying "well it's fitness" and calling it a day so much as they're honoring the explanatory power of a well confirmed theory.
No, logically it is proved true because it is assumed to be true and then used to prove itself.
> For starters, species go extinct all the time for reasons tied to their evolutionary trajectory.
Again, this is circular logic. You assumed that the only reason that species go extinct is because it wasn’t fit enough. If you assume survival of the fittest then of course it is true.
Here’s another circular explanation: things are the way they are because God created it that way. This explanation rises to the top precisely because it has explanatory power all across nature without evident counter-example, right?
In the end evolution is random, but exerts some pressure towards fitness in some environments. Some traits are legacy or are just plain random; just because an organism has a trait does not mean it is useful now, or indeed has ever been useful for fitness. The whole package must be reasonably fit for some environment, but that doesn’t mean all the traits improve fitness.
the part i think youre missing is that "survival of the fitness" is shown elsewhere, and used as a tool here to identify what the fitness is, and how and when certain traits were beneficial.
the case you are descibing is that all applicatioms of science(well, of anything) are circular reasoning. if you use newton's mechanics to predict motion of a mass undergoing acceleration, its circular because your result is proof of newtons mechanics, and newtons mechanics is proof of your result.
its just an "if and only if" relationship. that's not circular reasoning.
Also you don’t understand physics, the proof is that you can make predictions and then verify the results.
Again, I gave numerous examples, and you ignored mostly all of them.
Just to develop the point about extinctions a bit further. We know for instance of birds that had no natural fear of predators on the Galapagos Islands that upon human contact were driven to extinction or near extinction, and we don't need any circular assumptions to tie their fitness to their extinction.
And that's not to mention the rest of the examples I listed that you ignored, such as cases where we can observe that currently living species are doing well or poorly, like algae and pandas respectively, all of which hinge on knowledge of specific biological mechanisms.
So I don't know why you keep asserting that it's an assumption.