Natural Selection Explained Simply


Joe James


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everyone knows the phrase survival of the fittest and we also know it can have a few different meanings depending on when and how it's used but when we talk about natural selection where the phrase originated it's easy to assume that Fitness means best or literally the physically fittest but it doesn't what fittest really refers to is whichever members of the species are best suited to their environment and therefore more likely to be successful at reproducing and while this might sometimes mean actually fitter or better at doing something it's not a real requirement a month that is brown and lives in a pine forest is going to have more luck avoiding being eaten by predators than a white moth from the same species but there is nothing intrinsically better about the brown month it just happens to be better suited to its environment had the two months been living in a snowy birch forest the roles would likely have been reversed giving the advantage to the white moth who can now blend in more easily in any environment there are pressures to survive things like predators through scarcity and competitions for members of the same species these are called selective pressures and of course no environment can support an unlimited population which means only some members of the species will be able to reproduce when a population reaches its maximum in the case of the tiger there are only so many deer to eat and if tiger populations are high the environment cannot support them all or in the case of a deer all those extra Tiger mouths to feed mean deer going to find it harder to survive similarly in any species there is variation some moths are born brown some are born white some people have brown eyes and some people have blue the fastest strongest Tigers will be better at catching deal and will be the ones to survive while the slowest and weakest deer will become tiger food and the slowest Tigers may starve to death if there aren't enough to you let's look at how this plays out over time there is a forest of ten tigers and eighty dear this forest is a full capacity it can't support any more of any of the species each animal is ranked from fastest to slowest this variation in speed comes from the natural variation in every species just like you might naturally be faster than your friend to simplify just assume that tiger hunts have a success rate of one in ten and it takes one deer to feed one tiger for a year the first year the slowest ad ever come through it for the fastest aid Tigers and the slowest - Tigers unable to catch any of the faster do die from starvation so from both species the slowest have died off and the fastest now go on to reproduce passing on the genes for speed to their offspring by the next year both populations have grown beyond the limits of the environment to 108 deer and 12 Tigers since the deer are overpopulated the weakest third of the offspring die before reaching maturity and two of the oldest parish - as there is not enough grass to feed them all this leaves ninety four still above the forests carrying capacity this year's overpopulation means most of the deer awakened from scarce food and so all twelve Tigers are easily fed and twelve of the slowest deer are killed off all of the tigers go on to reproduce the following year the process is repeated for the deal who now massively overpopulate to 120 individuals this time three-quarters of the offspring died and twelve of the oldest deer died - due to a massive food shortage in the forest coming off last year's overpopulation of deer there are now 18 Tigers now that the deer population has stabilized back to eighty of the fittest members only eight Tigers are able to be fed this year and so the ten slowest Tigers starve to death this process continues over and over and results in each generation of birth' Tigers and deer getting faster because only the fastest of age species get to pass the genetics on resulting in on average faster generations as time progresses and although this is massively sped up and simplified hopefully you get the idea there is no intention behind the selection it is merely different species reacting and changing to the pressures of their environment this can be distilled into three points in any species there is variation in this example the variance was speed but of course there are many many different variations that can have an effect on survival all being played out at the same time note all members of a species make it to reproduction the slowest and weakest Tigers and deer were either hunted or starved before they were able to reproduce and genes are passed on from each surviving generation each generation inherited their parents traits for speed hopefully this has given you a basic understanding of natural selection remember that these examples are extremely simplified this video is the first of a three-part series if you don't want to miss the next to hit subscribe