That's a profound question. It's more of a philosophy question because "self" doesn't really have a scientific definition. Science is a powerful way of understanding the world, but there are some kinds of questions it can't answer.

I can say a bit about the brain, memories, and personality. We know that damage to certain parts of the brain, due to illness or injury, can change a person's personality and take away their memories. One famous example is a case of a railroad worker in the mid-1800s. He was using a long iron rod to pack explosive powder into a hole and the powder went off, driving the rod through the man's face and destroying most of the left frontal part of his brain (here's his story neurosciences and story ). He had been a nice guy who was easy to get along with, but the injury seemed to change him to a bad-tempered guy who just wasn't the same person, according to his friends.

Diseases like Alzheimer's can steal a person's memory and cause people who have been confident and trusting into suspicious, fearful people who think their loved ones are trying to harm them. Sometimes people with brain damage will have good days, when they seem more "themselves." So perhaps there is a part of their personality that is still inside them.

So what do you think? How might the answer influence medical or legal decisions? If this kind of question interests you, you may want to study the philosophy of science.

That is an interesting question Vishnav, and likely has different answers depending on who you ask. As individuals we all have different bodies and brains. Even identical twins, while they have the same DNA, have different experiences that lead to different memories. So I would say all three things make us individuals.

How do WE know we are individuals? Cognitive neuroscientist are trying to understand the regions of the brain that give us the sense of “self”. These studies are very interesting but something I know little about! Here is a link to a Wikipedia page that you may find helpful.
neural basis of self

The answer is "yes", all of them (body, mind, memory)make you yourself. No two humans are completely alike genetically (not even identical twins, thanks to mutation). On top of that, you have different experiences and memories. All of these things contribute to who you are. I believe that it is still actively debated what the relative importance of these different factors is, however.

Your genes make you different from anyone else. You get the half the DNA in your genes from your mother and half from your father, and with each parent giving you 3 billion base pairs of DNA, there's no way you share all of them with anyone else, unless you're an identical twin.

Then the environment makes each of them slightly different. The environment can even change our genes, in a process called 'epigenetics,' where -CH3 methyl groups and other little things are added to a few of the DNA bases, which does things like turning genes on or off.

Here's google's first answer to your question, by someone who has thought about the question more deeply than I have:
what makes you you

This guy writes entertaining posts. If you go to the end, you'll find links to other people who have thought seriously about the question.

There's a Psychology Today blog, it says your memories make you who you are. I'll argue that this is only part of the answer!

There are other interesting hits, if you just paste your entire question into a google search; but I'll let you find them for yourself.

A useful analogy may be to consider a snowflake. Every snowflake is made up of water molecules, which obey the same laws of physics and chemistry such that under the right conditions they spontaneously form into a self-organized structure, a snowflake. However, every snowflake is unique and different due to slight, imperceptible variations in the initial conditions.

Similarly, every person is made up of cells, which are made up of atoms, which obey the same laws of physics and chemistry. During development certain genes are switched on and signal certain cells to differentiate and form organs. Some cells will differentiate to become neurons, which subsequently form electrochemical connections with other neurons in the brain. Ultimately the millions of neural connections gives rise to consciousness. Even though we are all made up of the same biological material, every person is unique (including identical twins who have the same genetic makeup) because of subtle variations that occur during development and on into life. In physics this processes is called emergence ( emergence ), which is the theory that describes how the constituent parts of complex systems interact to form phenomena that emerge at the level of the whole.

The science of emergent phenomena was explicated by Philip Anderson in a 1972 article, “More is Different. ( more is different ).

Consciousness is one example of emergence since it arises spontaneously due to the millions of interactions of individual neurons. To a large extent, who you are is a result of the sum total of these millions of complex interactions. However, on an even larger scale individual humans interact to form self-organized systems such as economies, cities, and culture. So, who you are is also a product of the culture in which you live.

Thanks for the great question.

Scientists have identified three different, but related, reasons why each person is unique: genes, how those genes interact with different environments, and noise / personal experiences.

First of all, differences in genes can explain differences in people , sometimes in dramatic ways – for instance the presence of certain genes on the Y-chromosome determines if you have a male physiology. Differences in other sets of genes cause other differences that we see among people, including the color of their hair and eyes and how tall they can grow. In fact, every single human (putting aside identical twins) has a unique combination of genes that has never existed before and will never exist again. That’s unique.

Despite this, humans actually have a very high degree of regularities between them. For instance, nearly everyone’s heart is designed the same way and has the same function. If you opened an anatomy textbook from hundreds of years ago, you could still learn about the correct shape of the heart. So where do other changes come from if not just the genes?

Some features that differ between people are the product of facultative adaptations. This refers to genes that react to the environment in ways that help the organism survive. One example is the way skin tans. When exposed to lots of sunlight, genes that control your skin cells react by producing more melanin, toning the skin darker to protect the cells against intense sunlight. So facultative adaptations, the interaction of certain environments and certain genes, also explain differences between people.

A last important factor we can call noise or personal experiences. These are all the events that happen across a single lifetime that also make you unique. For instance, you could go to the gym a lot and gain muscle, or you might get a haircut. Such experiences, again, make each person unique, and influence who we are. Note, however, each factor affects every other factor – who we are is a very complicated story! Thanks again!