Btw did you know that in a single day, the DNA in your cells accumulate trillions of new random mutations? Thankfully, your cells have several mechanisms that detect and fix the most common mutations. Out of those that slip through, most of them occur on parts of DNA that don’t code for anything (most of your DNA), so they won’t have any effect. Out of those that occur on coding DNA, most of them will be too minor to have any effect still. Out of those that do have an effect, most of them will only have a small effect that only affects the mutated cell in question, so it won’t be a big deal. Out of those that have much more serious effects, like uncontrolled cell division that can lead to cancer, our cells have specific genes that are responsible for detecting these serious mutations and having the mutated cells self-destruct to prevent cancer. But sometimes, multiple mutations occur at the worst locations at the same time, so that even the genes responsible for cell self-destruction get mutated themselves and stop functioning properly. When this happens, most cancerous cells will get detected and destroyed by your immune cells. But sometimes, one will slip through your immune system as well, and only then will cancer develop. Sometimes, in very rare cases just through sheer luck, mutations will occur in specific locations in the DNA of your gamete (sperm or egg cells) so that they leave a beneficial effect in your offspring instead. This will make your offspring slightly more fit to survive compared to their competition, and this is how evolution basically works.