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Tuesday, May 18, 2010

Are we the same person that we were 10 years ago?

I have been doing a bit of research on this topic lately: I have written off a few myths, and pondered on others (for excessive lengths of time).
From a physical approach, I once heard that the cells in the average human were all different to the cells that had been there approximately seven years ago. I soon discovered that this was not true about all cells, such as brain cells. (I suppose this is quite clear, because if we lost all of those over a period of seven years, surely we wouldn't remember anything.)
From a mental and emotional approach, we are always changing our minds et cetera, but fundamentally we think in the same way as we did seven years ago.
I eventually came to the conclusion that for this question to be answered thoroughly, one needed to define "the same person".
I thought about this carefully. Could "the same" mean that even if we lost a few skin cells or a bump on the head made us forget a few things we would still be effectively the same person? Well, I actually don't think so. Even if we are 99.999...% the same, we are only partially the same. We are partially the same as every other human on the planet, and we don't call ourselves the same person. I like to think that "the same" should mean "exactly the same", and therefore with every instant (or frame, like in a film) we are somehow different than before. Whether it be that we are thinking different things, or that we have lost a couple of dead cells, or that our temperature has changed... anything.
And there you have it. At least, that's my view.


  1. I have to agree that we are only at best partially the same as we once were several years ago.

    Despite our genetic code, we are not just programs written in DNA. We suffer from the inherent errors of cellular replication, and other mutations. A given set of stimulus today may produce a different set of results tomorrow depending not just on how our cells are internally wired but how they interact with their environment. As the cells, their environment, chemical and electrical interactions are always changing then the we can never truly be the same from one moment to another.

    In software engineering we have a practice called re-factoring; this is performed when we want to re-write a piece of code to replace some chunk of functionality with the same services. In plain language, we remove old hard to understand or maintain code with easier to use code - the crux of this practice is ensuring that the new replacement code does exactly the same thing as the old. To do this we write tests to show that old behaviors seen for given inputs generate the correct expected out puts -- to an outside observer they should not know that anything has changed under the hood. So here's my thought, if given a set of questions (covering all aspects of knowledge to emotional reaction) and recording their results, if we were to redo the test 10 years down the road would having the same results mean that one has remained the same? Sure we know the physical difference, but can it be possible for a human to accommodate such changes and maintain the functional specification? If they do then can we say that they have not changed for all practical intents and purposes?

    Personally I prefer the idea of people changing over time, but give me ten years and ask again ;)

  2. Your idea of a test is really good, if only I were dedicated enough to follow it up that far down the track! But thanks for your ideas, it really is a fascinating subject, and even though I feel like I sit at the "I don't know much about this topic" end of the spectrum, I still enjoy thinking about it.