In his discussion of the Bramanti et al mtDNA paper, Dienekes states the following...
"
However, the evidence of this paper also contradicts the plain demic diffusion hypothesis. According to this hypothesis, farmer genes are gradually replaced by hunter genes as the farming economy spreads, because in each step there is a mix of farmer-indigenous populations which go on to colonize regions beyond the frontier. This is
not what appears to have happened. Rather, it seems the farmers moved across Europe with very little interaction with pre-farmers. A long period of no contact between the LBK and foragers is actually supported by
archaeology. I have termed this type of diffusion the "skipping stone":
In the
Skipping Stone model, farmers move out in search of new territories before they have started to blend with the local foragers; the genetic impact of the initiators of the movement is preserved".
This seems to be supported by the following paper, which claims that there was no real interaction in northwestern Europe between hunter/gatherers and the first farmers for at least 1000 years.
Forager-farmer connections in an 'unoccupied'land: First contact on the edge of LBK Territory, Bart Vanmonfort, p.9-12
https://lirias.kuleuven.be/bitstream/123456789/206831/1/Vanmontfort-forager.pdf
Dienekes take on it...
It is important to determine how long it took for indigenous populations and immigrant farmers to warm up to each other. The
rate of spread (in km/year; and
here) of the Neolithic may imply that by the time the farmer/forager societies started to blend, the wave of advance had already moved far away; the implication of this would be that the Neolithic bearers at the edge would have a smaller contribution from the indigenous populations of the regions they had already passed through.
On the other hand, the case may have been slightly different in the Balkans...
Dusan Boric et al, Strontium isotopes document greater human mobility at the start of the Balkan Neolithic.
http://www.pnas.org/content/110/9/3298.full
It seems that from the first arrival of the newcomers, there was interaction between the two groups...
From the paper: "New aspects of body decoration, such as the first appearance of
Spondylus and stone Neolithic-looking beads in burials placed in typical Mesolithic posture of extended supine inhumation at both Lepenski Vir and Vlasac (refs.
17 and
52 and
SI Appendix, section II and Figs. S4–S6), along with the appearance of other items of material culture (e.g., pottery, flint, polished stone axes, a new tradition of bone artifacts), confirm important changes were taking place in these forager societies that came under pressure from the growing Neolithic presence in the adjacent areas after ∼6200 cal B.C. (
14,
16,
17). This process of asymmetrical acculturation ended up in a complete absorption of forager specificity in the first several centuries of the sixth millennium B.C. ..."
The question arises as to why this happened so quickly in the Balkans and whether the disappearance of all the mesolithic cultures was because they left, died our or were incorporated. The authors of the paper take the view that they were incoporated.
From the paper: "The social ethos of these Neolithic communities might have been in large part aiming at incorporation of foreign groups encountered in parts of southeastern Europe, as a way of “domesticating the other” (
53). As for the Danube Gorges foragers, judging by, at first, a rather organic appropriation and incorporation of new elements of social and material existence as well as biologically “new blood” into the existing modes of being, and, consequently, the abandonment of forager cultural specificity, the mentioned process might have had a predominantly positive connotation or at least represented the only viable solution in the face of the emerging demographics."
By new blood, they mean that it is their view that there was mate exchange between the groups. From the paper:
"Of 10 nonlocal individuals associated with the Mesolithic–Neolithic transition phase I-II and Early/Middle Neolithic phase III at Lepenski Vir, all but one burial (no. 20) are females or possible females. This pattern could be interpreted as suggesting a reciprocal mating network between the Danube Gorges foragers and the earliest farming communities in the surrounding areas, with largely nonlocal women being buried at the central forager site of Lepenski Vir during these phases. "
That's certainly intriguing, but it's not DNA evidence. I hope the Bean Project includes some of these samples in their analysis.
Still, it seems clear that the pattern was slightly different in the Balkans. Perhaps it was a strategic decision by the farmers in the Balkans, as the paper seems to imply, to incorporate these people because they lived athwart the easiest and most direct route north and west. Also, the density of farmer settlement may have been much higher at the point of entry into Europe than it was in central Europe. Or, given the relatively empty spaces in central and northwestern Europe, the two groups there could for a long time essentially ignore each other.
I do think that if there was mate exchange in the Balkans, it might fit in with the comment made upthread that perhaps an adoption of the farming culture was made much easier if some farming genes were adopted first. I think that might have been true at a very basic level. I haven't thoroughly studied which mutations might be involved with the adoption of a mainly cereals diet, but just off the cuff, perhaps it's not a co-incidence that the highest levels of celiac disease are in northern and western Europe. Mutations must also have occurred among the farmers which provided some immunity to infectious diseases engendered by living in close proximity to domestic animals and, indeed, to relatively large groups of other humans.
As to other, more cognitive and psychologically based mutations, I think they must have existed as well. Farming requires not only sustained, often repetitive, and hard, physical activity. It also requires extremely long term planning. We very easily say that these people domesticated certain crops and animals, but it was a process that required great persistence and patience over a very long period of time.
I also don't know how much of our view of these supposedly far-roaming hunter bands is actually a romantic view of much earlier Paleolithic hunters of the tundra, rather than the actual situation for these Mesolithic people of Europe, perhaps more aptly named fisher/gatherers, who, as the vegetation in Europe massively increased, seem instead to have rarely moved from the ecological niches they had developed. In fact, at this particular period, they seem to have been much more sedentary than the Neolithic farmers. As the authors of this study point out...
"Our study unequivocally proves that in the earliest phases of the Neolithic in southeastern Europe, perhaps paradoxically, farming communities were much more mobile than local foraging populations, which in the case of the Danube Gorges remained tied to the exploitation of particular ecological niches since the beginning of the Holocene up until ∼6200 cal B.C. Conclusions reached by the strontium isotope evidence for the Danube Gorges region are corroborated by other archaeological indicators."
Also, the real adventure, it would seem to me, would lie not in seasonal trudges back and forth along routes known for milennia, but in setting off into the total unknown, with only a few animals, some seeds, and some paltry belongings. It's the settling of the west in Amercia times 10.
Finally, I'd just like to point out that farming culture might have had much more appeal for women in hunter gatherer communities than for the men. Much has been made of the fact that many infants died in Neolithic societies. However, what was the survival rate in mesolithic societies? Along with the high numbers of all H/G's that must have died from injuries sustained in hunting, especially if their resistance to blood infections wasn't very high, the death rate for infants must also have been extremely high, not to mention that it has been speculated that deliberate attempts were made to keep the population low. The hope, for a woman, that she might be able to keep more of the children she bore, would have been a powerful inducement.
Ed. As to the issue of violence between the two groups, the paper on the Balkans provides evidence for two heads, non-local in origin, found in a Mesolithic burial context. Again, however, it seems that the farmers ultimately prevailed.