I hope I got your attention now!
I am reading this book Evolution for Everyone and in this book, it states that the reason different personalities in animals and humans exist in the first place has a direct link to biological survival. Evolution devised different survival mechanisms as a result to enable greater chances of survival.
In a sense, a personality is merely a survival strategy to increase the chances for the species of creature to survive. Each individual survival strategy's (personality) efficiency rate of survival is dependent on the environmental conditions of the time, therefore each personality that exists today have all been at different times in prolonging the survival of the human race.
This is merely a theory, but I like to this is the reason different personalities exist and they don't just exist for show but for evolutionary purposes. Human beings have the harbor a variety of personalities. I'd like to hear your thoughts on this whether you are on agreement or disagreement of my hypothesis.