What is the best evidence that two organism share a common evolutionary ancesery

Vidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating the common descent of all life on Earth developing from a last universal ancestor. This evidence constructs the theoretical framework on which evolutionary theory rests, demonstrates that evolution does occur, and is able to show the natural processes that led to the emergence of Earth's biodiversity. Additionally, this evidence supports the modern evolutionary synthesis—the current scientific theory that explains how and why life changes over time. Evolutionary biologists document evidence of common descent by developing testable predictions, testing hypotheses, and constructing theories that illustrate and describe its causes. Hope you get it!

What do you mean about innate behavior i don’t get it