Relative fitness. It’s there in the figure I posted. It is defined and it is measured like that. The reproductive success of an organism relative to the reproductive success of it’s ancestor. And as you can see on the figure, relative fitness goes up:
They become better at reproducing than the ancestor. They literally multiply faster as the generations go by.
There is some ancestral organism that was used to seed the experiment. Then as the generations went on and descendants evolved, they got better and better at reproducing in that environment. They now reproduce close to 80% faster than the ancestor. They measure fitness by direct competition, where they mix up a solution of descendant bacteria with ancestor bacteria and let them compete directly, and then they measure how the fraction of the population changes over time. They show that the descendants outcompete the ancestor, as it grows in numbers much faster than the ancestor.
That seems to be a problem with you, not with what is being said. It’s perfectly straightforward English. Perhaps you should try and try put aside whatever is preventing you from comprehending what is being said. Some times you have to be willing to try to understand, which might require that you suppose there is something to be understood. If you can get yourself to read with a willingness to consider that there is something to be understood, you really can understand it. I know, because I understand it and it makes perfect logical sense.
It isn’t. It’s been defined, and the definition is sensible and coherent. And it can be measured. Descendants outcompete the ancestor in the same environment.
This is where Sanford and Price and all the GE types proceed to change the definition of fitness. Notice that it is they who do this. They want the bacteria to become more complex by adding new proteins and molecular machines, evolve more new functions in their genes, increase information in the genome (by measures they can’t define), speciate and turn into a giraffe, and fly out of the petri dish while shooting their human captors with X-men lazors. Otherwise it’s not the right kind of fitness in their mind. But then it’s THEM who are changing the definition.