From what I read, race is considered the biology, the physical traits inherited by ancestry. Ethnicity and nationality have to do with social construct and cultural identity. This is almost the same things as sex and gender, where the former means the biological characteristics, and the latter refers to the social identity.
So, is there any relationship between race, ethnicity, and nationality? For example, Asians have a different cuisine than Europeans, which consists of whole grain and wheat, which explains why they are generally shorter? What makes them have slanted eyes? Is it because they have been known to look up at the sun constantly that they developed that characteristic over time?
What makes Mexicans have black hair, brown eyes, and medium skin, or have higher foreheads? Again, does this have to do with the cuisine that they have, or something else?
The only explanation I have heard about race is that melanin affects the colour of the skin. It is always sunny in Africa, which is why Africans have really dark skin, despite the fact that all of humanity derived from Africa. Europeans lived in more cloudy weather, so their skin became paler. I'm sure there's more to these findings.