More ramblings on fitness

6 02 2007

Note: This post is actually quite a bit longer but the last 1/3 keeps getting lopped off. I will fill the rest of it in later when I figure out how to efficiently divide the ideas.

After writing my previous posts, I started thinking more and more about the idea of “fitness” in organisms, and why we should perhaps abandon the abstract and subjective concept of some creatures being more “fit” than others. The primary thought nagging at me was the idea that fitness is something that is passed on via the genotype and expressed in the phenotype, but there are so many more variables. In order to help my own mind get around the problem I took a trip to the Bronx Zoo this past Saturday, stopping by the World of Birds to look at their visual representation of Robin survival. The representation starts off with 100 eggs, some of which never hatch for various reasons (predation, fungi, bad parenting, etc.) This whittles the potential population down to 75, but of those fledglings a large number never develop much further as similar factors that reduced the number of eggs acts on the young birds as well. In the end, only a handful (I have to look at the photograph I took again, but I know it’s less than or equal to 15) make it through their first year. This doesn’t take into account that some of these birds may never mate or make their contribution to the next generation, so even if one of these birds had a trait that would enhance fitness but never mates because of early death/lack of a partner, the trait is lost (at least until it appears through mutation/variation again, if ever) with the death of that bird.

Going back to the eggs, any one of these eggs could hold an embryo that is potentially more “fit” than any other embryo, but if it’s unlucky enough to be squashed or eaten the evolutionary advantage it would provide is lost. How can we measure fitness of something that isn’t born yet? In of itself, a bird protected by an egg doesn’t seem very fit being that it is reliant on its parents for warmth, protection, and care, the ability of the parents to provide for the egg directly affecting its likelihood to survive. Even then there are other factors to consider, such as snakes, birds that “trick” other birds to care for their young by putting their egg in the nest, storms/weather, etc. Although we don’t often think that the “struggle for survival” starts before birth, it absolutely does, nearly making every birth a miracle given the hurdles a developing animal must overcome but cannot influence or change. This also reminds me of what has been observed in groundhogs or marmots in some areas, where if a subordinate female becomes pregnant and is discovered, the dominant female will harass her to the point where the developing rodents are aborted, thus any advantage any of them may have is never expressed or passed on. Hence, it is foolish for us to think strictly in terms of adult/developed animals when we consider the adaptedness of a species, the variables that affect development and selection being nearly innumerable.

What also irks me is that lack of consideration for intelligence and behavior in contemplating fitness, especially among mammals. Chimpanzees are not born with the knowledge of how to use tools to crack nuts or reach termites with sticks, but if they live in a group where they can be taught these skills their potential to survive goes up. In Africa different regions contain lions that engage in different hunting behaviors, the lions of the swampy regions of Botswana adapted to take down Cape Buffalo when elsewhere lions avoid such large animals, the cubs learning the skills from their mothers (hence the problem when “man-eaters” have cubs; they babies pick up the skill too). Were the cubs born knowing how to take down cape buffalo that other lions won’t touch? Not at all; they had to learn from their mothers how to do it. Although male lions live a fairly luxurious life compared to the females when grown, when they are kicked out of the pride to find their own territories they must fend for themselves and the tactics they practiced/learned in play come into effect as they cannot take down huge prey on their own, “teenage” males that can successfully stalk and catch smaller prey having more of an advantage than those that have not perfected these skills. If we are the gauge “fitness” in these situations we most certainly have to take intelligence into consideration as well, especially at an individual level; animals, like us, do not have a standard collective IQ and differing levels of intelligence or being more adept at certain behaviors will certainly affect survival rates in given conditions.

Furthermore, what if an organism is pushed out to the fringes of an environment; does that mean it is less fit because it was not born in an optimum habitat? Given the amount of plasticity to adapt to varying conditions, could an animal on the fringes be as fit (or even more fit) to a certain environment if allowed to move in? For all the reasons I’ve mentioned (and more, I’m sure), if we are to talk of fitness at all we need to make a distinction between potential fitness and actual fitness. In order to try and come up with a system to show this I made a half-assed attempt at math, using the robin example I mentioned earlier. If a particular developing robin is as fit to its niche (barring catastrophic events) as it’s parents, it has a 1:1 fitness potential. If it is more fit, it has a 1:1.1-2 fitness potential (the gradient allowing the amount of useful novel change to be expressed, and remember “fitness” can increase with learned behavior and development). If it is less fit, it has a 0.0-0.9:1 fitness ratio, 0 representing lethal mutation. This seemed reasonable, but the more I thought about it the more I didn’t like it and the more difficult my calculations in trying to show how this would work became; I would need a supercomputer to factor in all the random variables. Even if I was to successfully show changes in fitness, it wouldn’t be anything more than theoretical and it may not reflect what is observed naturally. Being that species are always changing as well, it would be foolish to arbitrarily mark the extant parents starting at a certain generation as 1, being that when the offspring of the parents had children you’d have to go back to the >1:1,




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