[Martin J Sallberg (OP)]

Why is it assumed that explanations of cultural similarities across the world based on contacts should assume a "center of civilization" originally surrounded by "barbarians"? Why is the third possibility, decentralized spreading of ideas stepwisely through neighbours of neighbours of neighbours, ignored? And why assume that a culture must have been isolated just because there is no absolute proof of contact? Would you assume that a DNA sample from a fossil was uncomtaminated just because there was no absolute proof of contamination?

The idea that biologistic explanations should somehow be better at explaining similarities across cultures than other explanations is based on the obsolete assumption of "evolutionary speed limits". The evidence for rapid evolution, especially from domestication/feralization research, shows that biologistic psychology makes racist predictions as inevitably as the theory of a lumniferous aether predicts annual changes in the speed of light in different directions. This cannot be explained away by "multifactorial inheritance buffering change". There are different forms of multifactoriality. Those based on addition can budge the average just as quickly as can single-factoriality. Buffer effects are only appliceable to threshold effect multifactoriality, and any buffer strong enough to save biologistic psychology from making racist predictions would have to be of the strength of phenotypic saltationism. And that a trait is needed to some extent does not mean that it is needed to the same extent.

In some cases, skewed definitions are used to support biologistic explanations. For instance, academia defines "matriarchy" far more strictly than it defines "patriarchy" (if the definition of "patriarchy" were as strict as that of "matriarchy" the existence of a few queens would have disqualified even medieval Europe from the "patriarchal" title) with the result that it is falsely assumed that male dominance should be hardwired. The formal definition of "matriarchy" is so strict that, even assuming that gender roles were distributed completely at random, it would be statistically unlikely that any tribe in the world should fulfil all those criteria (and because of the religion criterium, animal groups such as troops of bonobos would not qualify). So the absence of evidence for such does not prove any hardwired male dominance at all. There are tribal societies where women on average have more power than men, although they fall one or two criteria short of the formal definition of "matriarchy", and what specific criteria they fall short of varies. In fact, historical evidence for eunuch-dominated societies, especially in Asia, definitely falsifies the testosterone-based explanation of male dominance, at least on a "culturally universal" level.

As shown in "British journal of psychiatry" the increased frequency of autism in children of immigrants disappears if the parents immigrated many years ago, falsifying the vitamin D hypothesis. The theory that it should be due to stress during pregnancy does not hold up, since other stressing factors affecting pregnant women does not give such an autism statistic. This supports the theory that traces of culture are inherited by things such as epigenetics. That falsification means that studies of infant behavior is not valid as evidence for hardwiring at all. And some aspects of body language may be practical side effects of metabolism or sensory, not for communication at all. And if we are all descended from black Africans, how did blushing evolve?

Early monument building from the last ice age, such as Göbekli Tepe, falsifies the theory that it was climatologically impossible to build large enough communities in that era. There have also been many fluctuations in climate during the ice age, sometimes relatively warm periods lasting thousands of years. Why no cities from that time? Obviously people once thought differently, even those who looked sapiens. There is also evidence that some tribes in modern times have chosen to not build monuments despite having had the opportunities, extending those cases much further forward in time.

[cheryl j]

Why is it assumed that explanations of cultural similarities across the world based on contacts should assume a "center of civilization" originally surrounded by "barbarians"? Why is the third possibility, decentralized spreading of ideas stepwisely through neighbours of neighbours of neighbours, ignored?

Cities were found in ancient times and even in recent history on major travel and commerce routes, ports, etc. So even if a cultural innovation started in a remote area, it probably didn't spread very quickly or widely until it hit a city. Epidemics followed this pattern. Dumping on sick sailor on an isolated island would not have the same effect as letting him get off the ship in Genoa.

But, today, with the internet and social media, some cultural trends do pass from friends to friends of friends, and music is no longer controlled by a few major record labels.

[Martin J Sallberg (OP)]

Why is it assumed that explanations of cultural similarities across the world based on contacts should assume a "center of civilization" originally surrounded by "barbarians"? Why is the third possibility, decentralized spreading of ideas stepwisely through neighbours of neighbours of neighbours, ignored?

Cities were found in ancient times and even in recent history on major travel and commerce routes, ports, etc. So even if a cultural innovation started in a remote area, it probably didn't spread very quickly or widely until it hit a city. Epidemics followed this pattern. Dumping on sick sailor on an isolated island would not have the same effect as letting him get off the ship in Genoa.

But, today, with the internet and social media, some cultural trends do pass from friends to friends of friends, and music is no longer controlled by a few major record labels.

This does not rule out the possibility that contacts between proto-cities may have spread ideas far and wide, not just ideas invented in the city but also ideas invented around it.

[cheryl j]

This does not rule out the possibility that contacts between proto-cities may have spread ideas far and wide, not just ideas invented in the city but also ideas invented around it.

No it doesn't, just that innovations probably had to hit a city to become more widely spread. And innovations probably began with whom ever had the need for it or the materials to create it.

[dlorde]

... innovations probably had to hit a city to become more widely spread. And innovations probably began with whom ever had the need for it or the materials to create it.

There would also be a larger potential market (and, as you imply, it would be a market of individuals from a variety of places, suggesting rapid and broad distribution). One wonders if the start of trade between population centres was what triggered the rapid spread of ideas and innovations; as soon as a practical idea or innovation reached the nearest trading centre, it would rapidly be distributed throughout the trading network.