We can measure it.
For decades, every single year, scientists have visited the Galapagos and measured the beaks of a particular species of finch.
And year after year, with each generation, the beaks change, exactly as we'd expect from the weather patterns of the year before. Evolutionary biology works, and rigorous data collection backs it up.
For hundreds of years, though, science has gotten it wrong about gender, race and ethnicity. Eugenics and its brethren sound simple, but often lead to tragic outcomes.
The sloppy scientist says, "on average, across populations, left to its own devices, this group is [not as skilled] [neurotic] [hard to work with] [not as smart] [not as strong] [slower]" etc. They make assumptions without sufficient data, and the rigor is missing.
The first problem is that human beings aren't averages, they're individuals. And the bigger problem is that we're never left to our own devices. We are creatures of culture.
The math that we can do on populations of hedgehogs or pigeons doesn't apply to people, because people build and change and experience culture differently than any other species.
Your DNA is virtually identical to that of the hordes that accompanied Ghengis Khan, as well as most Cro-Magnon cavemen–pass one on the street and you wouldn't be able to tell that he's different from you. The reason you don't act the way they did is completely the result of culture, not genes.
It's culture that pushes us to level up, to dig deeper, to do things that we might not otherwise do. It's culture that finds and encourages and pushes people to become better versions of themselves than anyone else expected to find.
So it was sloppy/lazy/fearful science that said that women couldn't handle being doctors. And it was sloppy science that worked to limit the number of Asian or Jewish students at various institutions. And it's sloppy science that's been used against black people for hundreds of years.
And sloppy science said that a 4 minute mile was impossible and that a woman could never finish a marathon.
Sloppy because it doesn't include all the relevant factors. There's nothing wrong with the scientific method, but everything is wrong with using it poorly (and often intentionally).
What we need are caring human beings who will choose to change the culture for the better.
Not all of it, of course. Merely the culture they can touch. The people they can engage with. The human beings they can look in the eye, offer to help, offer encouragement and offer a hand up.
Once we reset the standard, it becomes the new normal, and suddenly, the sloppy science seems like phrenology. Because culture is up to us.
Sloppy science isn't science at all. It's the lazy or wrongheaded use of the scientific method part of the time, mixing in fear for good measure. Ignoring culture ignores the part that truly matters.
It's tempting to judge people by their DNA. It makes a lot more sense, though, to see people based on what they can contribute instead.