system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: "Race is a social construct"

I don't understand this. What is the explanation for race being a social construct if there are observed biological and physiological differences between different races? 

Clan mentality certainly is a social phenomenon amongst humans, but the catalyst of that clan mentality is race, and what race a person is is a product of biology and breeding. 

So, when I hear people argue "race is a social construct", trying to give it no credence, with an underlying social/political agenda, it makes me wonder how they can make such a claim when there obviously is an innate biological difference among races. 

Thank you so much! 

EDIT: Thanks for all of the awesome responses. Follow up question, what exactly is the difference then, between race and ethnicity? Thanks!
gpt
The problem is that we divide people based on superficial and largely irrelevant traits simply because those particular traits are easily visible.  As a result, all people from southern Africa tend to get lumped into a single category such as "black", even though most human genetic variation is found in those populations.  

To put it another way, two random black Africans are likely to be genetically more distant from each other than either one is from a random "white" European or Japanese, even though the common understanding is that these are different races in some meaningful way.  

And aside from that, all the different categories we can construct based on physical appearance are going to shade into each other anyhow.  Humans do vary quite a bit, but dividing them up based on gross physical traits obscures a whole lot more than it illuminates.  For instance, a person with one parent of mostly African ancestry and another of mostly European will generally be considered black in the USA but white in Haiti.  If that doesn't point to a powerful cultural influence on these classifications, then what does?