The definition of a clade doesn’t seem to have a “lower” limit. It’s just defined as “one common ancestor and their descendants”. So your mom, you and your siblings form a clade.

It doesn’t really help to segregate between different populations, since pretty much any clade large enough to include everyone of a specific population will include people outside that population.

A cline would apply, since it shows a very general trend of a specific trait creating a spectrum between regional differences. E.g. rabbits living in snowy regions tend to have white fur, while rabbits living in regions where there’s never snow tend to have brown fur, and anything in between is a spectrum.

This does apply to humans (e.g. people living in sunnier regions tend to have darker skin than people living closer to the poles), but the purpose of clines is specifically to show that these populations aren’t a completely separate thing that can be easily divided along lines. Instead, it shows that differences only become apparent when you look at the extremes and ignore all the in-betweens. It is specifically about the fact that you can’t just categorize populations into boxes.

In regards of clusters, I’m not exactly sure what you mean. Gene clusters maybe? They don’t really have anything to do with populations…

A big issue with categorizing people into “genetic boxes” is coevolution. Superficial details like skin color are comparatively easy to evolve. These traits are usually a factor of many different genes working together and mutating just one of them will result in darker or lighter skin tones. This means that coevolution is super easy and common. Light skin (dark being the actual default skin color for humans) has evolved many times over independently. So while light skin looks like a common genetic trait, it very much is not. It is instead something that evolved multiple times separately.

If a population of dark skinned people moves into a polar region or a population of light skinned people moves into an equatorial region it will not take long (maybe a dozen or two generations) for their skin color to adjust.

You can see the same with animals: It’s super easy to breed e.g. a dog with a specific fur color. It just takes a few generations of forced selection.

I don’t even know how to frame the issue as you state it. My knowledge of “clades” is that they’re used to group various sets of species that have something in common that isn’t otherwise represented by classic taxonomy. How… how would that apply to humans, anyway?

As for “clines” and “clusters,” I’m just now learning their meaning in genetics, but they seem to be at considerable variance with each other(!)

Human races? There’s no such thing. What century are you from?