I guess you should define what exact mechanism you’re describing when you use the term ‘group selection’. Richard Dawkins would describe the phenomena you mention (multi-cellular organisms and eusocial insects) as cases of the genes which create those complex phenotypes being selected.

In a group without exogamy, selection for the group is selection for those genes responsible for the complex phenotype that is the group, in a similar but less strict way. This is true even with sufficiently minor exogamy.

Right, but then you don’t need a mechanism other than genetic selection. Because that’s what is typically meant by group selection: that there is an additional selective mechanism that exists aside and apart from genetic selection.

Maybe we are talking past each other then. Because to me group selection is a type of genetic selection.

Then we are in agreement. Typically, group selection is not meant in that way, though. Just an FYI.

Yes.

I think a definition of "group selection" which includes either multicellular organisms or social insects would be extremely unusual, and basically misses the whole debate. Nobody is confused about why oak leaves sacrifice themselves every autumn.

The Pechenga Oak Tree is 2000 years. Imagine a cell line being content playing a support role. For thousands of years. Without trying to spread itself. I find that amazing and mysterious. Unless all long-lived lines in a tree have a shot at spreading?

There must be some interesting game theory to keep everyone aligned for that long.

Cancer is an instance of the tension you’re describing erupting into open rebellion as a lineage of cells starts over-consuming resources to the detriment of the organism (and all the other cell lineages contained in the organism). I’m not sure what your depth of knowledge is with regard to genetics and evolution, but a fruitful google search might be “germ line vs somatic cells”. This tension also exists at the level of DNA, with some fragments of DNA replicating themselves willy nilly all over the genome, rather than merely being replicated through the normal mechanism. And regarding the game theory: I think the typical thinking is that incentives are dependent on the mode of replication. If something replicates only when the organism creates offspring, then it tends to work harmoniously with the rest of the organism to further this goal. If it replicates via a different mechanism, such as a parasite or disease, then it tends to be uncooperative in collective endeavors.

In humans, even individual selection is pretty negligible as an effect. We breed too slowly, we're too homogeneous, there aren't enough of us, and we don't face anywhere near the kind of selective pressure most species do.

We absolutely face the same degree of selective pressure that other species do. You can clearly see that some people leave many descendants, whereas others leave none. The selective pressure we face is different though. Other species may be selected primarily on ability to extract food from the environment while surviving predation and disease, whereas we are being selected on our desire to have children.

The fact that some people leave many descendants while others do not does not necessarily imply the existence of strong selective pressure, particularly selective pressure for genetically heritable traits. For example, it could be mostly random, resulting in genetic drift that has essentially nothing to do with external environmental factors. By most definitions genetic drift is not natural selection, because it doesn't select for any particular attributes in the species, outside of preserving basic functional requirements (e.g. members of the species must be able to reproduce at a reasonable rate).

"Desire to have children" is a good example of something that does not obviously select for any particular genes. Many people who don't have children (or have only one) simply don't feel they can afford it, or (e.g. in China until recently) live somewhere where having extra children is a liability; while money is indeed heritable, selection against the poor or legally disadvantaged is not natural selection. Similarly, selecting for people who believe in a particular religion that encourages reproduction, etc. These things are not correlated with genetic markers to begin with so this "selective" process will just lead to more drift, or (if the population shrinks sufficiently) result in bottleneck events that lead to even more genetic homogeneity without selecting for any useful traits.

I'm not saying sexual selection isn't a thing, incidentally--but I am saying that there's very little evidence that sexual selection is the primary driver of whether humans reproduce.

This is qualitatively different from "real" natural selection, which requires a combination of any or all of: significant external stressors, significant untapped resources, a lot of generations, and a high population or mutation rate. We can see that humans are not under especially significant selective pressure when we consider that despite huge death tolls and a very strong negative effect on ability to reproduce, it will take a very long time (IIRC, on the order of 1000 years) before a large majority of people in any area of the world are naturally resistant to HIV.

Out of your four claims, zero are true.