The science on this is clear: the Human Genome Project, completed in 2003, found that people share about 99.9% of their DNA. There is more genetic variation within so-called racial groups than between them. European scientists and colonial governments built the categories we use, then ranked them.
But "made up" doesn't mean "not real." US law made race real in its effects. The Naturalization Act of 1790 limited citizenship to "free white persons." In 1923, the Supreme Court ruled that Bhagat Singh Thind, an Indian immigrant and US Army veteran, couldn't be a citizen. The Court said that even if he was "Caucasian," he wasn't white in the common understanding (Equal Justice Initiative). That ruling stripped citizenship from other Indian Americans, too.
You can also see the construct shift over time. Under the one-drop rule, anyone with any known African ancestry was classified as Black, even if most of their ancestors were white (PBS). Meanwhile, Irish and Italian immigrants were once treated as nonwhite and racially inferior. Their skin color stayed the same while their place within whiteness changed, and some earned it by joining in the oppression of their Black neighbors (Irish Times).
So race is a social construct, and racism is still very real. The lines between groups have moved many times. But the laws and institutions built around those lines still shape who gets wealth, health and safety today.
Common questions
What does it mean that race is a social construct?
It means people invented racial categories and decided who belonged in each one. The categories reflect history and power, not deep biological differences.
If race isn't biological, why does it matter?
Because laws, institutions and people have treated race as real for centuries. Those choices still shape where people live, what they earn and how healthy they are.
Is there a genetic basis for race?
Not in any meaningful way. Humans share about 99.9% of their DNA, and there's more variation within so-called racial groups than between them.