A little while back I remember learning about something within genetic evolution that really surprised me. Genes that are immediately next to each other on a chromosome tend to stick together during cellular division. Physics is at play in the way that chromosomes line up and pull apart during cellular division and the separation of genes in both eggs and sperm. This can have a strange effect on how some genes get passed along. Imagine you have a gene that is crucial for survival, such as a gene that codes for whether lungs develop and a gene that is somewhat negative for survival, like a gene that makes your immune response a little less effective. If these two genes are immediately next to each other on a chromosome, then they will likely be passed along together, because it would be hard for them to be separated. If you don’t get the lung development gene, you also don’t get the weak immune system gene, but you don’t develop in the womb. If you get the lung development gene, you also get the weak immune system gene. The genes are passed along in the standard evolutionary process, but one gene seems actively harmful to survival.
I share this story because it demonstrates that genetic evolution is more complex than I had ever thought. I hadn’t considered the way that physics could influence which genes are passed along. Scientists could spend time trying to find exactly why a weak immune system gene is beneficial for survival and what competitive advantage that gene gave to a species for it to be favored by evolution. However, the real answer would just be that the gene was stuck next to a more important gene, so it kept getting passed along. An inadvertent deletion that would have inactivated the weak immune system gene may have also damaged the lung development gene, making it more likely that evolution would favor the two genes being passed along without errors together.
Looking at more complexity within genetic evolution, Yuval Noah Harari in his book Sapiens writes, “a microorganism belonging to one species can incorporate genetic codes from a completely different species into its cell and thereby gain new capabilities, such as resistance to antibiotics.” We think of evolution as a chain, with organisms and species slowly evolving as random typos provide advantages or disadvantages to a species. But this is too simple of a model as Harari’s quote shows. A microorganism can take in genetic information from outside, completely transforming that organism in a single generation.
Science also knows, however, that this kind of genetic adoption is not limited to microorganisms. There is evidence that sweet potatoes evolved when a virus infected a potato plant and inserted its DNA into the plant. The potato adopted DNA from a different organism and started down a new evolutionary path toward becoming the modern sweet potato. This sounds like a very niche and strange thing, but it is something humans are now exploring through CRISPR technology that may be able to cure many genetic disorders.
Genetic evolution is not a simple chain. It is much more complex than we think, and there is likely more we will discover that will demonstrate how complex the system truly is.