What is fitness?

The $64,000 dollar question. :slightly_smiling_face:


Of course, one way to confuse others while maintaining plausible deniability (even to yourself) is to confuse yourself first.


I see various people saying fitness applies to a specific environment when that’s what @PDPrice said and you’re also criticizing him for saying so. What am I missing?

1 Like

Uhm no, he’s being criticized for complaining about the fact that fitness is defined in context of a specific environment. He apparently thinks this is a sort of statistical lie or sleight of hand, because he wants things to get higher IQ and longer lifespans(or whatever).

But that’s his own problem, not a problem with the theory of evolution. I must repeat myself, the theory doesn’t say and was never intended to say that different abilities will always stack up in numbers and degrees. That’s just not how the theory works.

The theory can explain it when this occurs(if they aid reproduction in some environment), but it doesn’t say it always will or should happen under all circumstances.


No that’s not what Price and Carter said in that CMI article. They claim we should only consider fitness as some undefined absolute (i.e higher IQs, greater strength) with no regard for the environment.


You’re right. It’s almost like the population is climbing up a fitness peak. Sure wish someone would have thought of that already . . . Oh wait, they have.

Reference? Quote???

Added in edit:

In fact, Darwin seemed to indicate just the opposite:


And there’s the sleight of hand. You have replaced fitness with damaging changes. This allows you to arbitrarily decide what is and isn’t damaging so you can reject any and all evolutionary changes. Let’s see how that works.

Evolution from single cell to multicellular. This is obviously damaging because the organism has lost the ability to be a single celled organism.

Multicellular with tissue specialization. Again, this is damaging because specific cells lose function in order to specialize.

Fish to terrestrial tetrapod. Again, an obvious example of a damaged species because they lost the function to live in the water.

I could go on and on with any old example you want. I can arbitrarily decide that any evolutionary change is “damaging”. Just look at how the poor little polar bear is damaged to the point that it couldn’t last more than a week in the Sahara desert.


It seems like this professor thinks so too, based a a few pages I read. https://discourse.peacefulscience.org/t/edgar-and-evolution/12430/476?u=thoughtful

Ok - see above where this gets confusing. All this emphasis on reproduction reminds me of the Miller-Morris debate and Miller was asked what death was and he referred to a professor who said death is sex and sex is death. It sort of shocked me. This continuous emphasis on reproduction when talking about evolution, instead of the interesting aspects of evolutionary theory is weird and sad to me. Not that science cares what I think about it but I assume when people think about evolution they think about adaptation and traits, not reproduction.

Or like proto-bats 52 MYA who had mutations lengthening their finger bones and changing their paws into wings. The lost the ability to not fly. :wink:


Reproduction is one of the mechanisms that drives adaptation. At first, the new adaptation will only be found in a single individual. In order for that adaptation to become common in the population the original carrier has to pass that trait on, and the descendants of that original carrier have to do the same. If the carriers of that new adaptation reproduce more than those without then the adaptation becomes fixed in the population.


I got that. I feel like we’re discussing what came first - the chicken or the egg?

I just noticed something -

Is fitness relative to its own species at a specific time or relative to its ancestor?

The egg came first. The ancestors of chickens were not chickens, but they laid eggs. The reason that chickens lay eggs is that they are the descendants of egg layers. Again, reproduction.

It is relative to all of the members of a species that are living at the same time in the same environment. For example, human skin color correlates with latitude. Higher melanin protects against the damaging effects of the sun near the equator while less melanin allows for higher vitamin D production in the higher latitudes.

I can’t think of a reason to compare traits to ancestors, but others may have examples.


Both can be measured, but obviously what drives the evolution of some population over generations is the competition among all individuals currently present and competing for resources.


Now you are changing definitions. What’s actually measured along the y-axis in that experiment?

How is it comparing one trait to another currently present?

I thought evolution, in terms of competition, was a dead idea as well.

Better to say allele.


No, I haven’t changed the definition at all. I’ve told you what drives evolution, and how they measure fitness in that experiment.

Relative fitness, in direct competition between descendant at some generation (shown on the X axis) and ancestor used that founded the experiment.

Then you thought wrong. Why did you think that?


You should take that up with Sanford, then. The definition is crystal-clear.

What do you think about the evolution of the sexual dimorphism and dances of male Birds of Paradise?

That’s entirely about reproduction. I got to see two species last March, btw. They are incredible.


This is a different definition than relative fitness above. It changes the definition to survival rather than a comparison of reproduction amongst species with different traits.

The emphasis on reproduction is important to understand how evolution works and how natural selection contributes to the evolutionary process. It’s not meant to imply that is the only interesting aspect of evolution. Nor that natural selection is the only process that can or does contribute to evolution.

Yes I think so too, and those are also interesting questions to ask. How, historically, did some adaptive trait evolve? But to answer that question we need to consider the ancestor in the environment it used to be part of over the period of time when that trait first evolved. This is where we need to consider reproduction again, and the environment in which this evolution occurs.


Than what definition above?

No, I haven’t changed the definition to survival rather than comparison of reproduction. I have a hard time believing you are this bad at reading comprehension. What’s really bothering you?