Answer:
Happiness is a way to socialize with others. Since human's though intelligent, are weak when fighting against a bear per say; We're strong in numbers. The only issue is how would the early humans communicate and stay together? By having emotions, sadness, anger, happiness, etc we can communicate these feelings to potential mates, and groups in order to survive.
The feeling of happiness is from a chemical labeled, dopamiene. This is the cause of happiness, and our bodies naturally boost the production of it in certain situations. Like consuming a chocolate bar, usually production levels of dopamiene will increase.
Hope that helped!:D
Step-by-step explanation: