Silarities between people is a very interesting topic for a thesis !
To me, similarities allow people to connect with each other because most of the time the human being is looking forward to socialise with people like him in a way. It can be a similar life goal, or a similar Hoby, or even a similar friend !
But in the same idea, a lot of people are trying to be different from those they know . But it can be true in order to do/be sth like someone else or just in order to be the only unique human being to be like this.
Humans are naturally curious and easily go to people that they rely to. But sometimes we want to get our own voice and be the different one, the Unique one...
In most species of animals this is also true ! Our best friend is very often the one we want to be like or its complete opposite, the one we absolutely don't want to be like ?
This so interesting, it's really a good topic, if I wanna do or debate or sth like that I am sure that it will be an awesome one !
Good luck for your project ;-)