Similarly: we all come from an unbroken line of people who had children. It may be that throughout history not having kids is common. Gay people who never had children may have been common. Ugly, poor or unpleasant people who never managed to find a partner may have been common. Asexual people may have been common. Straight people who had sex but never had kids were probably not common, just because good contraception wasn’t available. Still, if you’re a person who, for whatever reason, is not going to have kids, none of your direct ancestors can understand that life.