By Lucas W. (8th Grade)
over time
The theory of evolution is the idea that over time, mutations combined with natural selection causes species to differ greatly from their ancestors based on their living environment. I will now attempt to explain this theory using a very odd example – that humans and, say – E. Coli – are related.
cells
One piece of evidence supporting this link is that all living things have cells. Even though the cells are quite different (Notably eubacteria do not have a nucleus, the dna just floats around), they are still obviously cells by the existence of a membrane, cytoplasm, and ribosomes.
single cell organisms
These single cell organisms have cells differing far from the eukaryotic cell, which is what humans are made of. But what about analogous structures? It is very possible that this could be by chance, that they evolved separately, similar to the wings of a bat and the wings of a bird. But the thing is, we actually have a chain of species with small differences in each one to show this.
First, we need to find a point that we know is related to humans. How about the old world apes branch, containing the human and just 23 other species? By tracing back some time, we see that this branch is part of the primates order. By continuing further back, we trace back the similarities to the mammal common ancestor, which then traces back slowly, past the vertebrae ancestor, until the single cell early eukaryotic organisms show up. By going further back billions of years, we then see ancestors of the many archeon groups, before joining back to LUCA, the last universal common ancestor. LUCA’s genome is unknown, but we have made good guesses based on early archeon and eubacteria’s shared genes. By reversing course, we see the first branch to split off of this common ancestor is eubacteria. by continuing along the course, we end up in the escherichia branch, on which we see E. Coli.
DNA
But where is the proof that this is true? What if this data is wrong, what if we messed up somewhere and the cell structure similarities are also by chance, even though they are so small? Well, we can compare DNA. Because by reading out all this DNA, we see mutation by mutation that changed the cells from LUCA to archeon to eukaryotes to humans. Although no shared genes remain between us, this is because E. Coli is a very different ancestor. And so, because of the wildly different environments we have developed in, the wildly different genes we have gotten from a once identical set, this is just one piece of evidence backing up the theory of evolution.
