Differences in the human genomes of our global populations is helpful towards unraveling our history. Consider the question, How did agriculture spread 10,000 years ago. As irrelevant to our subject as this subject seems, remember that when people migrate they take their genes with them. Thus, deciding whether agriculture was spread by the spread of ideas or of farmers can be investigated using the different alleles that individuals in the populations. In a classic study, Cavalli-Sforza accumulated genotypes at 95 alleles for several hundred individuals from 26 present-day European populations. Allele frequencies among populations were summarized by Principal Components. The first component of a principle components analysis recovered 28% of the variation in the data. When mapped to globe the PC1 showed migration from the Middle East, reflecting the spread of agriculture by migration.
The arrival of agriculture is thought to have originated in the Middle-East and propagated as a "wave" through Europe with the earliest in Greece and the latest in northern Europe.
The technological advance of agriculture allowed an increased population density from the Palaeolithic hunter gatherers.
Genetic analysis suggests that the first PC represents this spread due to the date (post the last glacial maximum) and geographical distribution are strikingly similar.
The genetic evidence shows that the wave of agriculture assimilated the previous populations giving a genetic distribution across Europe with the maximum of Neolithic genes in the south east and the minimum in Scandinavia, thus outdating the "migration" theories.
The spread of agriculture can be seen in the arrival of wheat from the Middle-East. Ceramic pottery arrived in Europe around the same time with differing regional forms.
The spread of Indo-European languages into Europe from a "homeland" either in the middle east or north of the Black Sea has been suggested to be associated the spread of agriculture.
PC1 correlates with Eu4 [incidentally, this is a YAP+ lineage that probably derives from Ethiopians() within the past 20000 years], Eu9, Eu10, and Eu11. This component has been "proposed to reflect the diffusion of Neolithic farmers". That may be it's primary cause, but it may also incorporate earlier and later migrations from the Middle East.
mtDNA patterns are also consistent with a Neolithic expansion from the Near East. ()