Group selection can roughly be defined as a form of natural selection by which the fitness (probable reproductive success) of the group is maintained or enhanced, even at the cost of reduced fitness of individuals in that group.
In considering group selection it is worth having a definition of what constitutes a group of the type capable of acting as a selection pressure on the individuals composing the group; since the minimal requirement of group selection is the presence of a suitable group that is stable (in those key respects which enforce selection) over a sufficient number of generations.
(Most of the ways of conceptualizing groups selection are, I believe inadequate)
This question can be reduced to the definition of a biological entity.
A biological entity is a (relatively) concentrated and sustained network of communications and interactions. Thus a single cell, a multicellular organism, an organ (such as the heart, or a gland) within a multicellular organism, and the social group in social organisms may all be considered to be entities.
For example, in social animals (including humans) that which makes them social animals can be defined as a sufficient density of particular types of communications and interactions between individuals - sustained across sufficient numbers of generations - such that this acts upon the individuals to shape behaviour by mechanisms that are transmissible between generations (for example, by inducing genetic, or some types of epigenetic, change of individuals).
In other words, the group itself displays a system-autonomy from the individuals which compose the group - therefore the group itself is a selection pressure on the individual animals within the group.
What is meant by autonomy? That the group entity operates to sustain and expand and/or reproduce itself - this being a defining property of all complex systems.
If an emergent complex system (occurring by chance) were to lack the ability to sustain and reproduce itself, it will soon simply cease to be - and would not be observable (or only momentarily so).
This is because a system is defined in contrast to its environment, and the basic property of a system is to separate itself from the environment in a context where chance/ entropic change will tend to assimilate the system into the environment (e.g. this happens after death).
Therefore any complex system which is sustained, must have the ability to sustain itself - to re-make and re-produce itself in the context of its environment - and for social groups individual organisms are a part of its environment. Therefore, social groups are buffered against the individuals which constitute it - but this is not a paradox, because what makes the social group definable as a complex system is the interaction of inter-individual communications, therefore not the actual physical individual organisms.
So, when we consider group selection of humans, we should be looking at the frequency and complexity of communications between individuals. from this perspective, I think we can see that the emergence of complex agriculture will have had the effect of increasing the density of inter-individual communications by expanding both the size of the social group and also the necessity for planning, specialization and coordination of agricultural (and also industrial) economic activities - with the extra communications necessary to enable this.
What about the industrial revolution? From a communications perspective, the key factor about the industrial revolution is expansion of the population, and a much more extensive but less concentrated network of communications. I would conjecture that the switch from face-to-face to written (and later digital) interpersonal communications was associated with a great reduction in the complexity of communications.
Direct, face to face communication is informationally far richer, far denser, than the abbreviated, abstract, precise but simplified communications of electronic media (or than the preceding bureaucratic communications such as 'memos' and the 'minutes' of meeting). So, it is likely that industrialization is associated with a reduction in the complexity of group-level entities, and a reduction in the strength of group selection - and therefore with the re-emergence of individual level selection.
Hence, modernity is characterized by increased atomism of individuals, increased individual versus individual competition; and a loss of the strength of 'communities'. This will lead onto changes among individual humans, to make them more individual and less adapted to group cooperation.
In conclusion, it is reasonable to assume that in human history, group selection was strengthened by at least some forms of agriculture; and that individual humans in complex agricultural societies are more strongly group selected than the individual humans in 'simple' hunter-gatherer societies (i.e. 'simple' hunter gatherers are those without either food storage or complex technologies).
In terms of genius, which Dutton and I argue (in our forthcoming book The Genius Famine) to be a group selected phenomenon (with the genius serving a specialized function to benefit the reproductive success of the group), this fits with the historical evidence that some types of complex agricultural society seem to provide the optimal selective environment for producing the highest density of geniuses - since these are probably the most group selected of societies.
