The shared DNA is one of the most important aspects of evolution. It means that genes don’t have to be constantly totally invented. What changes is the timing and amount of time of the expression of different genes. For example apparently there is not a separate gene for the long neck of a giraffe. Rather there is a genetic mechanism in giraffes which turns the neck length gene on much longer than it is on for most developing embryos. This mechanism works for many different aspects of development in all creatures and plants. Thus, it does not take nearly as long to develop new species as it would if they had to be developed from scratch. Shawn Carroll wrote a fascinating book on this called “Endless Forms Most Beautiful.” A very interesting read.
Thanks. I’ll check it out.