In biology, we talk about organisms alone and in groups. So far, we’ve been concerned mainly with individual organisms, which together form populations. Those populations of organisms combine with other populations in order to form communities, and those communities come together with abiotic factors to form entire ecosystems. As we’ve already seen, those ecosystems can be grouped together as a biome when they exhibit similar climates. So, when we study ecosystems and evolution, we are concerned with how the populations in those communities change.
When you look at a population of humans, there are always certain similarities and differences that you notice. For instance, skin color, hair type and color, eye color, average height are all genetic characteristics that are the easiest to notice about people. Biologists don’t just study humans; we study all sorts of living things.
Imagine that you were looking in a field of butterflies: you see thousands that have yellow and black coloring and also a few dozen that have blue and black coloring. You also notice that there are hundreds of birds hunting the butterflies. Before we look at the behavior of the birds, we can make a conclusion about the gene frequency of the yellow color among the butterflies. Specifically, we can say that the gene frequency of yellow is around 99%, because 99% of the butterflies have yellow instead of blue. Similarly, we can say that the gene frequency of blue is about 1% for this population of butterflies.
Gene frequency, or the percentage of individuals in a population that have a certain characteristic, is a way to measure evolution. Going back to the butterflies and the birds, you notice that the birds are only hunting the yellow and black butterflies. For some reason, they are leaving the blue and black butterflies alone. You leave and come back a week later to the same field to find that there are only a few hundred butterflies; what’s more, half of them are now blue and black butterflies!
This is an example of evolution – in this case, the population of butterflies has changed. The gene frequency of yellow coloring has decreased to about 50% because of changing environmental conditions. What were the “changing environmental conditions”? The birds that were hunting the butterflies made the change in the butterfly population. Even though the total number of butterflies has decreased, the blue and black butterflies are surviving better because of the hunting patterns of the birds.
We have seen that there are many factors that go into making a biome: temperature, precipitation, animals, plants, mountains, rivers, oceans, etc. All of these factors affect the evolution of the living things within the biome.