https://www.cell.com/ajhg/pdf/S0002-9297%2818%2930363-X.pdf

"Genetics demonstrates that humans cannot be divided into biologically distinct subcategories."

"Most human genetic variation is distributed as a gradient, so distinct boundaries between population groups cannot be accurately assigned."

etc.etc.

You can only make that claim by examining a single locus. When you examine multiple loci, human populations are clearly separated into distinct groups. The fact that this oft repeated myth is so commonly addressed that it is a named fallacy should be an indication that it warrants a little investigation into its accuracy. Here's a handy graph to help visualize how Lewontin's claim is dishonest and false: https://ars.els-cdn.com/content/image/1-s2.0-S03069877090053...

If you want to argue about the science, please research the subject first. There's no way anyone could do even a cursory bit of research and not come across this as it has been beaten to death, resurrected, and re-beaten to death.