What makes you you and what makes me me? What makes us different and what makes us the same? And why are we human beings, not cats or bees or plants or mushrooms or germs?
The answer to these questions is chemistry – a special kind of chemistry that allows life to exist on Earth…
All living things are made up of building blocks called ‘cells’. In biology, there are many types of cells, all with different jobs to do. For example, your skin cells help to keep you alive by keeping your insides on the inside and acting as a barrier to keep things that might hurt you out!
And inside every cell of every living creature, is a special chemical called ‘deoxyribonucleic acid’ (or ‘DNA’ for short). DNA is a complicated biological molecule that acts as a code, giving all living things the information they need to be alive. And the information they need to be a particular type of creature. You can find out more about DNA here.
As I explained in my answer to how does a seed know what to grow into?, the DNA code for each type of creature is different. The code for a human is not the same as the code for an antelope or a cherry tree or a mould. So, an insect is an insect because the cells in its body all have the DNA code (or the instructions) to make it an insect. And people are people because their cells contain the DNA instructions to make them human beings.
So why are you and I and all other people not exactly the same? Well, the code for a person can have some variations (or small differences) that make us each unique as individuals without making big enough changes to turn us into a new type of creature. So, although we can see differences in people’s eye colour, hair colour, skin colour, height and other physical characteristics, we are all human because almost all of the DNA in our codes is the same.