Similarly, original sin is a derangement of human nature. We sin because we are not capable of living sinlessly. This inability to live correctly is original sin. It entered human nature as a result of Adam's sin. But it's now present in each of us.
Various theologians have ideas of how original sin is passed on to the next generation.
However none of these theories is generally accepted, so I do not regard them as necessary parts of the idea. Original sin has been widely believed by Christians. In Rom 7, Paul discusses the problem of the sin that dwells in all of us. The current doctrine can be traced at least to Augustine. It was strongly held by Luther and Calvin.