How we Witness Fitness
“Survival of the fittest” is one of those phrases that you learn in school that never leaves you. It’s one of the ideas of biological understanding that can always be used to explain evolution to just about anyone. After all, it is one of the key mechanisms of natural selection.
Great, but what does it mean and how it is observed? Well, first, we must explain fitness. Biological fitness, paradoxically, has little to do with how much you can bench. The term really means how much you reproduce. So, if you are fit to survive until reproduction, your lineage will continue on and on. Pretty simple, right?
Well, sort of. As is often the case in nature, how things are executed can vary widely. Two gorillas fighting or birds doing some impressive dances are some of the more impressive methods. The males of these species must be able to demonstrate their reproductive fitness to a mate, which has the final say in whether the male’s genes are passed on. While these are the methods that might first come to mind, they’re not the only ways.
Cuttlefish, an animal that I’m sure I’ll come back to in future posts, have a more cunning method shared with several other animals across the kingdom. Some male cuttlefish are what we call “sneaker males.” These males appear female and will hang around the dominant males, who battle and chase off other males, until they can sneak in to mate with females. Dastardly? Yes. Devious? Sure. Effective? You bet. Though not a risk-free alternative, it is a method that can work quite well for males in certain populations. In fact, some scientists believe that sneak mating cuttlefish are more successful (and therefore fit) at mating than dominant males.
Other animals take this a step further. Raising offspring requires effort, so why put in the effort? Make someone else do all the work! Cowbirds are an example of this, they’re nest parasites that insert their young into other bird’s nests and let them do all the parental care. It’s a fairly high risk, high reward strategy though. If it works, no need to invest effort into your offspring. If not, well, try again later?
Humans, as you hopefully know, put a lot of work into raising a small number of children or a single child. Society helps too, but that’s a different conversation. Human babies are not known for their rapid physical development, and unlike some mammals, our offspring are not up on their feet and walking within the hour. So, if it’s some much work, then why have we evolved this way? Well, since we put so much work into one or two offspring, they are very likely to survive and pass on our genes, thus demonstrating our reproductive fitness. A lot of effort into a low number of offspring means that they are very likely to survive. It’s the method we see in many mammals, like primates or elephants, but what about other groups?
Many do the opposite. Think sea turtles. Many eggs, many hatchlings, many potential chances, but there are few results. Why? Well, they don’t invest much effort into their offspring. “Lay ‘em and leave ‘em,” if you were. Taken even further, some fish simply deposit their eggs and sperm together and are done with that. It doesn’t get any more low effort than that. And yes, this method works well. Many offspring with a low chance of survival is also a successful reproductive strategy. If at least one survives? Fantastic, you’ve produced one offspring that will carry on your genes to the future.
This is what must be considered when thinking about reproductive fitness: no matter how you breed or how many offspring you produce, as long as one reaches adulthood and reproduces too, you’re fit for survival.