Some contemporary Lockeans, such as Lynne Rudder Baker, say that you were never a foetus. This raises the question: what happened to the foetus?
The most popular answer is that the foetus grew up and became an adult human organism. But this organism, which is the adult version of the foetus, is not you – you were not a foetus. So, there are two closely related things, you and the organism. Now the organism has a brain and a nervous system etc, so it seems as if the organism can think. But then aren't there too many thinkers standing where you are, since there is both you and the organism? Worse, presumably the organism is having the same thoughts that you are having. So how do you know that you are not the organism after all?