What do scientist mean when they talk about organisms having a common ancestor?

im sorry

Explanation:

I cant help you ask someone else I have not covered that in my biology course

Similarities in genetic code

When two organisms share a common ancestor, their genetic code has to be similar. The extent of similarities determines how recently have the organisms evolved. For example, all life on earth shares the genes responsible for essential biological processes such as respiration which means that all organisms evolved from a common ancestor called Last Universal Common Ancestor(LUCA).