Eli5: What’s the biological reason behind humans having eyes(irises) of different color?

Question

I know that eye color is directly related to the amount of melanin present in the front layers of the iris. But what’s the biological need behind different color?

In: 98

Answer 1

Brown eyes, like dark skin, are better suited for sunny climates, as sun protection. Light eyes, like light skin, is a mutation that survived in less sunny climates. It just means the eyes have less pigment – blue eyes aren’t actually pigmented blue, they just reflect the blue light (which is why they can look grey at times)