Port Charlotte chambered cairn

Port Charlotte chambered cairn is located on the Rinns Peninsula in the west of Islay (NR 233 584; CANMORE ID 37313) (Figs 2 & 3). It is one of six such monuments on the island (Fig. 2; Mithen Reference Mithen2021) and one of two that has been excavated in the modern era to provide radiocarbon dates, the other being Nereabolls (see below). Excavation in 1976 identified its façade and a chamber with four compartments (Harrington & Pierpoint Reference Harrington and Pierpoint1980). Finds from the chamber included human bones, three leaf-shaped arrowheads, flint knives, sherds of five Neolithic vessels, and charcoal that provided two radiocarbon dates, both falling into the mid-4th millennium bc (Table 1). Although the charcoal samples were unidentified, causing a risk of old wood, the dates are stratigraphically consistent with those from pre-cairn activity. CANMORE records the bones as having been accessioned into the Islay Museum, but this appears not to have occurred (Islay Museum, pers comm). There is no known report on the bones and their whereabouts remain unknown.

An occupation horizon below the cairn was described as containing over 2000 flint flakes, charred hazelnut shells, and fragments of sheep bone, this providing three further dates falling into the 4th millennium (Table 1). There is no published report of these finds and hence the technology of the flint remains unknown. Connock et al. (Reference Connock, Finlayson and Mills1992) suggest the bones might be from roe deer rather than sheep, raising a possibility that the pre-cairn deposit is culturally Mesolithic rather than Neolithic.

Newton

Newton is located close to the head of Loch Indaal, 10 km to the east of the Port Charlotte chambered cairn (NR 34179 62830; CANMORE ID 37769). Excavations in 1988 identified a Mesolithic occupation dated to the early 6th millennium bc and a sample of features associated with Neolithic pottery (McCullagh Reference McCullagh1989). The Neolithic features consisted of narrow grooves c. 20 cm wide and 25 cm deep. Two ran parallel to each other for about 20 m, with one continuing at an angle for a further 5 m. Another groove cut these at an approximate right-angle. Some had stake-holes along their bottoms, with a further cluster of stake-holes and pits found nearby. McCullagh interpreted the grooves as the remnants of a fence line, repeatedly rebuilt. The fence, or whatever the grooves represent, had been constructed over a pit containing Neolithic pottery and charcoal, while a second pit had been dug over a groove line to hold a massive post. Both pits provided radiocarbon samples that dated to the 4th millennium (Table 1). The proposed fence was interpreted by McCullagh as representing an initial attempt at farming. This was supported by near-by pollen evidence indicating weed species associated with arable cultivation and pastoralism, although lacking any traces of cereal pollen. If correct, such farming was unsuccessful, with no further archaeological traces at Newton until the Bronze Age, while the pollen record had soon become dominated by heather, bog myrtle, and other plants indicative of increasing soil acidity (McCullagh Reference McCullagh1989).

Bolsay

The Mesolithic site of Bolsay is 2.5 km south-west of Port Charlotte chambered cairn. It is inland at 70 m OD on the lower slope of Beinn Tart a’Mhill (NR 227 571; CANMORE ID 70280). Following reports of microliths being collected from a ploughed field in the 1960s, the site was located by test-pitting through pasture in 1989 and excavated in 1990 and 1992 (Mithen et al. Reference Mithen, Lake and Finlay2000b; Reference Mithen, Lake and Finlay2000c). The test-pitting recorded an extensive and dense scatter of NBI artefacts. Charcoal from amidst a cluster of NBI artefacts within a test-pit provided a late 3rd millennium date (Beta-32236, Table 1). A 7 × 4 m trench was excavated in 1990 to establish site stratigraphy and gain a sample of artefacts. A radiocarbon date from a sealed feature indicated activity in the mid-7th–late 6th millennium bc (Q-3219, Table 1). Although this date provided an ideal fit with the material culture, the charcoal was not identified and hence could be old wood, giving a spuriously early date. This trench, and the 1989 radiocarbon dated test-pit, were encompassed by a 20 × 15 m trench in 1992 that focused on mapping the spatial distribution of finds within a 5 cm spit (Fig. 4). This involved the excavation, wet sieving, and sorting of material from 4429, 0.25 m² square quadrates.

Drawing on sedimentary, geochemical and micromorphological data, artefact distributions, and the location of 19th century field drains, the settlement was identified as having been adjacent to a natural spring located on a gentle slope. Primary occupation was on the dryland immediately above the spring, where flint knapping, tool manufacture, the use of coarse stone tools, processing of hazelnuts, and use of wood from hazel, alder, birch, and oak occurred. Post-holes and stake-holes may have related to shelters but were too few to discern patterning. The spring cut into the slope, forming a step below which small pools of standing water and an expanse of boggy ground was formed. Gradual downslope erosion of sediment occurred from the occupation area into the boggy ground, this containing flint debris, discarded tools, and wood charcoal (Fig. 5). Some waste appears to have been deliberately discarded into the boggy ground, while there were periods in which this area evidently dried out because features had been cut through it and then sealed by further sediment deposition. Activity is also likely to have occurred directly on the sometimes-boggy area itself.

Fig. 5.

Macro-debitage and microlith distributions at Bolsay (after Mithen et al. Reference Mithen, Lake and Finlay2000c).

The quantity of finds was considerable: 329,667 pieces of NBI chipped stone were recovered, estimated to be 20% (at most) of that within the pasture at Bolsay and including almost 12,000 microliths, microburins, and truncations (Fig. 6). In comparison to other Mesolithic sites on Islay, Bolsay has a high frequency but narrow range of retouched artefacts; although a wide range of microlith forms are present, the microliths are dominated by scalene triangles (Finlay et al. Reference Finlay, Finlayson and Mithen2000). Together with the large quantity of artefacts and their limited spatial patterning (Fig. 5), these features imply many short-term visits to an especially ecologically attractive location for a specific task, most likely hunting deer (Mithen Reference Mithen2000b). Beinn Tart’Mhill is known today as a favoured location for red deer hunting, as reflected in its name derived from the Old Norse for ‘Stag Mountain’ (Macniven 2015). The spring and nearby wetland of Loch a’Bhogaidh, with evidence of woodland exploitation from the 6th millennium bc onwards (Edwards & Berridge Reference Edwards and Berridge1994), and ready access to beaches rich in flint pebbles (Marshall Reference Marshall2000), would have made Bolsay a particularly attractive location for a Mesolithic hunting camp.

Fig. 6.

Selection of microliths from Bolsay (after Mithen et al. Reference Mithen, Lake and Finlay2000b).

Forty-seven coarse stone artefacts were recovered. Of these, 31 are elongated pebble tools, eight are hammerstones, four stone flakes and two unworked pieces, as typically found on Scottish Mesolithic sites. One of the remaining pieces is a perforated stone, found within the dryland area, which has been flaked but not polished and was likely the weight for a digging stick or a fish-net sinker, of which no other examples are known from Mesolithic sites (to my knowledge) (Fig. 7).

Fig. 7.

Perforated stone, leaf point and fragment of polish stone axe from Bolsay (Mithen et al. Reference Mithen, Lake and Finlay2000c).

While dominated by NBI artefacts, the Bolsay assemblage also contains two diagnostic Neolithic artefacts, a leaf point and the blade end of a ground stone axe made from locally available stone (Fig. 7). Both were found within what would have been the boggy, downslope area. The axe had been broken in antiquity, probably during use. Several flake scars extend below the fractured surface all around the axe head. Their number suggest they are unlikely to have derived from accidental mis-hits during manufacture, while they are not sufficiently extensive to suggest the reflaking of the broken axe for rehafting. The impression is of broken axe head used as a platform core. A small number of other artefacts might also reflect post-Mesolithic activity although these are not culturally diagnostic: multi-platform, amorphous and bipolar cores that had been reworked after patination; a petit-tranchet derivative arrowhead; several double-sided and convex ‘thumbnail’ scrapers.

Pottery was recovered: 655 heavily fragmented and abraded sherds were intermixed with the chipped stone and dispersed throughout the former dryland and boggy areas. A sample of 180 sherds represented four fabrics, with the large majority being undecorated body sherds. Two sherds are from Early Bronze Age beakers, one decorated with twisted cord impressions and the other with comb impressions. Only four others were decorated, three with incised lines and one with a row of nail impressions. Apart from the two beaker sherds, the assemblage is undiagnostic.

More than 10,000 pieces of wood charcoal were recovered, these also intermingled with the chipped stone in the former dryland and boggy areas. Eight samples of wood charcoal were selected for radiocarbon dating, supplementing the two dates acquired from the 1989 test-pit and 1990 trench, both of which were encompassed within the 1992, 20 × 15 m trench. The samples were randomly chosen from across the former dryland and boggy areas (Table 1). Of these, one indicated activity in the mid-7th millennium bc, one in the 6th millennium, four in the mid–late 4th millennium, and two in the 3rd millennium. The absence of 5th millennium dates is commensurate with the rarity of such dates throughout western Scotland, attributed to climate-induced population decline (Wicks & Mithen Reference Wicks and Mithen2014; Mithen & Wicks Reference Mithen and Wicks2021)

Storakaig

Storakaig lies 5 km to the east of Newton at c. 115 m OD (NR 3963 6264; CANMORE ID 304908) (Fig. 8). It consists of a c. 18 × 13 m area of organic-rich sediment underlain by clay and sealed by peaty topsoil, containing at least 80,000 NBI chipped stone artefacts intermixed with charred hazelnut shell and heavily calcined fragments of animal bone, primarily from red deer, roe deer, and wild boar (Wicks et al. Reference Wicks, Pirie and Mithen2014). The site is interpreted as a repeatedly used, upland hunting camp.

Fig. 8.

Excavation at Storakaig, August 2011. The site location is marked by the white polytunnel in the lefthand image (photo: Steven Mithen).

Storakaig was sampled in 2010–11 by a 9.5 × 7 m trench located within its western extent. Twenty out of 7539 catalogued artefacts have characteristics suggestive of the Neolithic. These include relatively broad, regular blade fragments that may be retouched, used, and/or occasionally truncated. Several artefacts have regular invasive retouch, including two knives and various flakes, while others have ad hoc ‘tangs’, some of which also have invasive retouch. Such characteristics have been considered diagnostic of Neolithic assemblages (Edmonds Reference Edmonds1995), although Islay lacks Neolithic chipped stone assemblages for a direct comparison. These artefacts were found scattered across the site, indistinguishable from the diagnostically Mesolithic artefacts in their condition and patination.

Eight radiocarbon dates were obtained from fragments of charred hazelnut shell recovered from within the artefact and bone-rich deposit (Table 1). The returned dates straddled the late 5th and early 4th millennia bc, suggesting activity was spread over 610 years, most likely taking the form of multiple short-term visits (Wicks et al. Reference Wicks, Pirie and Mithen2014). The 5th millennium dates overlapped with those from the Oronsay middens suggesting a mobile settlement pattern exploiting both coastal and terrestrial resources. Based on ethnographic records of hunter-gatherer mobility (Kelly Reference Kelly2013. table 4.1), the annual range of single residential group exploiting Islay and Oronsay would have also encompassed Raschoille Cave and Carding Mill Bay.

Nereabolls

Nereabolls chambered cairn is 2 km to the south-west of Bolsay and hence just 4 km south-west from the Port Charlotte cairn (NR 2015 5642; CANMORE ID 37355). This site was originally named Slochd Measach and is known locally as the Giant’s Grave. Although partially obscured by peat growth, the cairn had evidently been extensively robbed and was in a poor state of preservation when surveyed by the RCHAMS (1984).

Survey and excavation were undertaken in 2015, 2016, and 2017 to investigate pre-cairn activity, the architecture of the Neolithic monument, and its use in later prehistoric and historic periods (Maričević Reference Maričević2017; Maričević & Mithen in prep.) (Fig. 9). Regarding pre-cairn activity, four areas of a buried soil were exposed at the base of trenches in different areas of the site. Three provided radiocarbon dates falling into the 4th millennium, while a further date of this period was acquired from the fill of the cut for the chamber (Table 1). The fourth area of exposed buried soil produced a leaf-shaped arrowhead and a flint flake, with charcoal that provided a 2nd millennium bc date.

Fig. 9.

Excavation at Nereabolls chambered cairn, August 2011 (photo: Steven Mithen).

When constructed, the monument had a chamber with four compartments, a massive façade, and cairn constructed with stone slabs and rubble that likely extended for 30 m in length. Activity in the forecourt had continued until 3368–3105 cal bc. Small cists for the deposition of pottery vessels had been constructed within the rubble of the partially collapse cairn during the 2nd and early 1st millennia bc, with extensive robbing and re-use of the site occurred during the latter half of the 1st millennium bc and recent times.

Cherry-picking or an uncritical acceptance of dates?

Each scenario involves a level of risk regarding either cherry-picking supportive radiocarbon dates or uncritically accepting dates that may be contaminated or derive from redeposited material. The swift succession scenario must explain why 12 single entity samples from contexts associated with NBI technology fall into the mid-4th millennium bc or later, these coming from Bolay, Lussa River, Gleann Mor, and Rockside, none of which was identified as potentially contaminated by the laboratories and, when available, their δ¹³ values are within the expected range. Citing ‘contamination’ for these samples but not others might be considered as cherry-picking dates that conform to chronological preconceptions while rejecting others that challenge the conventional notion of a swift Mesolithic–Neolithic succession. Otherwise, why would seven of the dates from Bolsay be contaminated but not the remaining three? Why would two of the dates from Rockside be contaminated but not the third?

An alternative means to sustain the swift succession scenario is to claim the post-mid- 4th millennium dates at Bolsay, Gleann Mor, Rockside, and Lussa River are intrusive into Mesolithic deposits from later prehistoric activity. Other than at Bolsay there is no evident case for this because there is no known later prehistoric activity within the vicinity of Gleann Mor, Rockside, and Lussa.

Might post-depositional disturbance at Bolsay have mixed-up charcoal from Neolithic and later activity with the NBI artefacts deriving from 6th millennium and earlier Mesolithic activity? The seven 4th and 3rd millennium dates are difficult to accept as intrusive. How would such marginally represented Neolithic activity in this area – just two diagnostic Neolithic artefacts compared to almost 12,000 from the Mesolithic (microliths, microburins, and truncations) – generate 70% of the radiocarbon dates when the samples were randomly selected from over 10,000 pieces of wood charcoal/charred hazelnut shell? One might imagine a large Neolithic fireplace generating considerable quantities of charcoal which then became dispersed by post-deposition mixing. This, however, would be special pleading and fails to accord with the evidence. There are no traces of large fireplaces and the character of the Bolsay wood charcoal and charred hazelnut shell – its fragmentation, species representation, pervasive and unform distribution – is entirely consistent with that found at Mesolithic sites elsewhere on Islay, such as Storakaig, Gleann Mor, and Rubha Port an t-Seilich.

Neither the dual population nor the biocultural merger scenarios need to ‘explain away’ the post-mid-4th millennium dates from Bolsay and Lussa River by contamination or intrusive charcoal. Both models could also accommodate the 3rd and 2nd millennium dates from Gleann Mor and Rockside as indicative of a ‘very long Mesolithic’ (for the dual population) or the continuation of NMI technology within a merged population (bioculture merger).

Accounting for settlement and economic continuity in western Scotland

The swift-succession scenario appears incongruous with the evidence for settlement and economic continuity between the Mesolithic and Neolithic throughout western Scotland (Armit & Finlayson Reference Armit and Finlayson1992; Reference Armit, Finlayson, Pollard and Morrison1996; Mithen et al. Reference Mithen, Pirie, Smith, Wicks, Whittle and Cummings2007). On Islay, this is represented at Bolsay and at 14 undated artefact scatters containing NBI and non-NBI technology (Mithen et al. Reference Mithen, Lake and Finlay2000b; Reference Mithen, Lake and Finlay2000c). At Kinloch, Isle of Rum, the archaeological remains attributed to the Mesolithic and Neolithic are almost identical in terms of their chipped stone technology and types of features, although microliths and blades are less common in the Neolithic component (Wickham-Jones Reference Wickham-Jones1990); a bifacially worked leaf point was recovered from a pit containing charred hazelnut fragments. Both Mesolithic and Neolithic people used the shell midden sites of Oronsay (Mellars Reference Mellars1987), Ulva Cave (Bonsall et al. Reference Bonsall, Sutherland and Lawson1991; Reference Bonsall, Sutherland, Lawson and Russell1992), and An Corran (Saville et al. Reference Saville, Hardy, Miket and Ballin2012), although the sites may have been used for different purposes (Milner & Craig Reference Milner, Craig, Allen, Sharples and O’Connor2009). At Risga, a leaf-shaped arrowhead made from Rum bloodstone was recovered from the shell midden (Pollard Reference Pollard and Young2000), while a flake from a polished stone axe of Antrim porcellanite was found within the microlithic scatter at Lussa Wood, Jura (Mercer Reference Mercer1968). Although there are traces of Mesolithic settlement in the Western Isles (eg, Church et al. Reference Church, Bishop, Blake, Nesbitt, Perri, Piper and Rowley-Conwy2011; Reference Church, Bishop, Blake, Nesbitt, Perri, Piper, Rowley-Conwy, Snape-Kennedy and Walker2012; Bishop et al. Reference Bishop, Church, Clegg, Johnson, Piper, Rowley-Conwy and Snape-Kennedy2013), that available is too sparse to comment on Mesolithic–Neolithic settlement continuity. Intriguingly, occupation may have begun at Eilean Dòmhnuill on North Uist prior to 3720–3510 cal bc (Copper & Armit Reference Copper and Armit2018) and, hence, has the possibility of being Mesolithic.

The dual population scenario explains such technological mixes by use of the same location on different occasions by contemporary Neolithic and Mesolithic populations, living within separate communities but with a sufficient degree of interbreeding to have created the Raschoille Cave genome. The biocultural merger scenario suggests there is a single population with a chipped stone technology that made both microliths and leaf points.

Use of the same locations in western Scotland need not imply continuity in diet and economy. Schulting and Richards (Reference Schulting and Richards2002; Richards & Schulting Reference Richards and Schulting2006) used isotopic analysis of human remains to argue the Neolithic people had excluded marine foods from their diet, these being a Mesolithic mainstay. Their conclusion has been challenged on methodological grounds (Milner et al. Reference Milner, Craig, Bailey, Pedersen and Andersen2004), claiming it to be partially incorrect for ‘Neolithic’ individuals at An Corran (Milner & Craig Reference Milner, Craig, Allen, Sharples and O’Connor2009) and Carding Mill Bay (Bownes et al. Reference Bownes, Ascough, Cook, Murray and Bonsall2017) but with Schulting et al. (Reference Schulting, MacDonald and Richards2022) arguing the Carding Mill Bay re-analysis is methodologically invalid. Whatever the correct interpretation of the isotopic data, the quantity of samples remains too sparse to make generic statements about Mesolithic and Neolithic diet in the coastal regions of western Scotland, especially for the entire duration of these periods.

The rarity of Neolithic archaeobotanical assemblages from western Scotland also leaves the contributions of plants to the Neolithic diet, and overlap or otherwise with that of the Mesolithic, as unresolved. Bishop et al. (Reference Bishop, Church and Rowley-Conwy2009, 87) noted an absence of cereal remains from the west coast of mainland Scotland and the Inner Hebrides although a single grain of barley has since been recovered from Nereabolls. Bishop et al. (Reference Bishop, Church and Rowley-Conwy2009) also noted a continued use of hazelnuts in the Neolithic. A possible indication of continuity comes from Staosnaig, Colosany. Its scale of hazelnut shell exploitation, with their shells potentially used as a glowing fuel source within a large pit (Mithen et al. Reference Mithen, Finlay, Carruthers, Carter and Ashmore2001; Mithen Reference Mithen2019), suggests feasting of a type not dissimilar to that proposed for the Neolithic in the Outer Hebrides (Copper & Armit Reference Copper and Armit2018).

Interbreeding and the maintenance of demographic viability and food security

The swift succession scenario assumes interbreeding occurred soon after the Neolithic arrival and was quickly followed by the extinction of the Mesolithic population and culture. The dual population scenario allows for a longer period of interbreeding on an intermittent basis between independent populations; if such interbreeding was frequent, any meaningful distinction between the populations would collapse leading to biocultural merger. While interbreeding may have arisen for several reasons, one motivation – whether consciously articulated or not – may have been to sustain the demographic viability of a local community, whether Mesolithic or Neolithic.

As noted above, the Mesolithic population of western Scotland is always likely to have been demographically fragile, only just above the minimum viable threshold of c. 150 persons. As White (Reference White2017) explained, the viability of small populations can be enhanced by relaxing marriage rules. While he was writing about rules within a hunter-gatherer population, the relaxation of rules between populations/cultures would also compensate for the random and potentially fatal fluctuations in the balance of males and females of reproductive age. Interbreeding with a migrant Neolithic group may, therefore, have been a group decision made by a demographically fragile Mesolithic community. An alternative perspective is that of Mesolithic individuals, whether male or female, seeking to follow the Darwinian imperative of ensuring their own reproductive success by interbreeding with Neolithic migrants.

Likewise, for the Neolithic migrants themselves – they too needed to remain demographically viable. With the notoriously treacherous coastal waters of western Scotland it is difficult to envisage large numbers of colonists having originally arrived in western Scotland, nor for that population to have been continually replenished by new arrivals. Other than the chambered cairns, which may have been constructed soon after arrival, the Neolithic population on Islay is almost invisible, with only Newton and sparse finds of leaf points suggesting a presence. The conservatism of Hebridean pottery in the Outer Hebrides throughout the 4th millennium bc (Copper & Armit Reference Copper and Armit2018) also suggests a low population density, one lacking the capacity for innovation and change (cf. Shennan Reference Shennan2001). The proposed collapse in Neolithic populations throughout Britain and Europe that occurred a few centuries after initial colonisation (Collard et al. Reference Collard, Edinborough, Shennan and Thomas2010; Shennan et al. Reference Shennan, Downey, Timpson, Edinborough, Colledge, Kerig, Manning and Thomas2013; Bevan et al. Reference Bevan, Colledge, Fuller, Fyfe, Shennan and Stevens2017; Colledge et al. Reference Colledge, Conolly, Crema and Shennan2019) may have been a cause of, or further exacerbated, the marginal viability of the Neolithic population in western Scotland.

The proposed collapse is based on the analysis of summed calibrated probability distributions of radiocarbon dates from 12 regions of Europe, involving rigorous statistical tests to control for sampling variation and features of the calibration curve (Shennan et al. Reference Shennan, Downey, Timpson, Edinborough, Colledge, Kerig, Manning and Thomas2013). Having shown a marked boom in the inferred population during the first half of the 4th millennium bc, reflecting Neolithic immigration and farming, Scotland has one of the most significant collapses seen within Europe. The reason for the European-wide collapse remains unclear, although soil degradation from intensive cereal cultivation and a shift to greater reliance on livestock systems appear significant (Steven & Fuller Reference Stevens and Fuller2012; Reference Stevens and Fuller2015; Bishop Reference Bishop2015; Colledge et al. Reference Colledge, Conolly, Crema and Shennan2019), Bevan et al. (Reference Bevan, Colledge, Fuller, Fyfe, Shennan and Stevens2017) favour a climate driven population collapse. As Shennan et al. (Reference Shennan, Downey, Timpson, Edinborough, Colledge, Kerig, Manning and Thomas2013, 4) note, irrespective of the cause, Neolithic population decline would have inevitably influenced their economy and society. It may have driven local communities to relax their marriage rules to allow interbreeding with local Mesolithic groups and/or motivated individuals to interbreed to maintain their own reproductive success.

The Neolithic population of western Scotland may have also been impacted by local environmental factors. While there is no consistent pattern towards or away from warmer and wetter conditions in the late 4th millennium bc (Schulting Reference Schulting2010), Tipping (Reference Tipping, Finlayson and Warren2010) suggests that climatic instability may have been significant – just as we see today with local communities challenged by alternating periods of droughts and flooding. Sediment cores from Islay indicate notable periods of storminess at 3955–3810 and 3255–3040 bc (Kylander et al. Reference Kylander, Soderlindh, Schenk, Gyllencreutz, Rydberg, Bindler, Martinez Cortizas and Skelton2020). The likely failure of initial attempts at cultivation at Newton (McCullagh Reference McCullagh1989) might be an example of the wider decline of cereal farming as identified by Stevens and Fuller (Reference Stevens and Fuller2012), even if cereal farming continued longer on other Scottish islands than it did on the mainland (Bishop Reference Bishop2015; Stevens & Fuller Reference Stevens and Fuller2015). This may have driven the Neolithic migrants on Islay and elsewhere in western Scotland to supplement their pastoralism with hunting and gathering – for which they may have required Mesolithic-type knowledge and technology.

Dual population and biocultural merging in continental Europe

It is useful to reflect on the Mesolithic–Neolithic interaction scenarios for western Scotland from the perspective of continental Europe, where the genomic database is substantially larger. This indicates Mesolithic populations had a longer, varied, and more profound impact on the Neolithic than initial interpretations of demic diffusion and swift-succession scenarios implied (Lipson et al. Reference Lipson, Szécsényi-Nagy, Mallick, Pósa, Stégmár, Keerl and Rohland2017).

The ‘hunter-gatherer resurgence’ in Neolithic genomes within continental Europe at c. 4500 bc indicates that after initial Neolithic colonisation, dual populations were present for centuries throughout the region, with the Mesolithic hunter-gatherers remaining archaeologically invisible (Brandt et al. Reference Brandt, Haak, Adler, Roth, Szécsényi-Nagy, Karimnia and Möller-Rieker2013; Haak et al. Reference Haak, Lazaridis, Patterson, Rohland, Mallick, Llamas and Brandt2015; Lipson et al. Reference Lipson, Szécsényi-Nagy, Mallick, Pósa, Stégmár, Keerl and Rohland2017; Fernandes et al. Reference Fernandes, Strapagiel, Borówka, Marciniak, Żądzińska, Sirak and Siska2018; Jensen et al. Reference Jensen, Niemann, Iversen, Fotakis, Gopalakrishnan, Vågene and Winther Pedersen2019; Rivollat et al. Reference Rivollat, Jeong, Schiffels, Küçükkalipçi, Pemonge and Alt2020). Detailed analysis of the genomic data indicates the hunter-gatherer resurgence arose from multiple local populations of hunter-gatherers rather than from one source (Lipson et al. Reference Lipson, Szécsényi-Nagy, Mallick, Pósa, Stégmár, Keerl and Rohland2017; Lazaridis Reference Lazaridis2018), resulting in a complex pattern of population interactions (Fernandes et al. Reference Fernandes, Strapagiel, Borówka, Marciniak, Żądzińska, Sirak and Siska2018).

Analysis of genomic-data from 101 individuals from France and Germany by Rivollat et al. (Reference Rivollat, Jeong, Schiffels, Küçükkalipçi, Pemonge and Alt2020) confirmed the long period of co-existence between LBK and hunter-gatherer populations in south-west Germany – a dual population scenario. Relatively swift biocultural merger appears more applicable to southern Europe where the genomes of the Neolithic colonists have a significantly higher Mesolithic contribution than those in continental Europe. Neolithic material culture was also more evidently influenced by that of the Mesolithic in southern Europe, with observations by Rivollat et al. (Reference Rivollat, Jeong, Schiffels, Küçükkalipçi, Pemonge and Alt2020) building on Guilaine and Manen’s (Reference Guilaine, Manen, Whittle and Cummings2007) notion that Mesolithic population has ‘perpetuated’ itself in the Neolithic system.

The existence of dual populations within restricted regions of northern Europe is illustrated by those on Gotland during the 4th and early 3rd millennia bc (Fraser et al. Reference Fraser, Sanchez-Quinto, Evans, Storå, Götherström, Wallin, Knutsson and Jakobsson2018). Two groups co-existed for several hundred years with separate cultural identities, lifestyles, and dietary patterns, one with greater use of marine protein and deriving from an indigenous Mesolithic population and the other reliant on terrestrial sources and arising from migrant farmers, the Pitted Ware Culture and Funnel Beaker Cultures respectively. The extent of genetic admixture is yet to be determined (Fraser et al. Reference Fraser, Sanchez-Quinto, Evans, Storå, Götherström, Wallin, Knutsson and Jakobsson2018, 331). At c. 3000 km², Gotland fits comfortably into the area of the Inner Hebrides (c. 4000 km²) and is approximately the same latitude north as the Isle of Islay. A site specific example is the burial site of Blätterhöhle, Germany. A combination of isotopic and genomic analysis demonstrated the co-existence of a Neolithic farming community and a ‘Neolithic’ foraging and fishing community for over 2000 years, with the latter having a much higher degree of Mesolithic ancestry (Bollongino et al. Reference Bollongino, Nehlich, Richards, Orschiedt, Thomas, Sell, Fajkoova´, Powell and Burger2013). Such location sharing provides a precedent for that at Bolsay within the dual population scenario for western Scotland.

Mathieson et al. (Reference Mathieson, Lazaridis, Rohland, Mallick, Patterson, Roodenberg and Harney2015) note the hunter-gatherer resurgence is also represented by the re-appearance in Europe of the Mesolithic tradition of extended supine burial, this replacing the Early Neolithic tradition of flexed burial and suggesting a shift towards complete biocultural merger. This appears to have been driven by the movement of hunter-gatherer males into the farming communities (Gamba et al. Reference Gamba, Jones and Teasdale2014; Mathieson et al. Reference Mathieson, Lazaridis, Rohland, Mallick, Patterson, Roodenberg and Harney2015). Such integration may have been for the provision of hunter-gatherer environmental knowledge and technology into Neolithic communities, as proposed by González-Fortes et al. (Reference González-Fortes, Jones, Lightfoot, Bonsall, Lazar, Grandal-d’Anglade, Garralda, Drak, Siska, Simalcsik and Boroneanţ2017). They detected a cline across eastern Europe with greater Mesolithic–Neolithic genetic admixture in northern regions, suggesting a ‘progressive mixing with local hunter-gatherers and the acquisition of local knowledge’. That might also be applicable to the far north-west of Europe, with the environmental knowledge of Mesolithic hunter-gatherers in western Scotland being an attractive resource for the Neolithic immigrants to acquire, especially in the context of demographic stress and food insecurity from farming.

Ethnographic analogies

The feasibility of both dual population and bioculture merger is evident from the ethnographic record. This has well-documented studies of hunter-gatherers living alongside farmers, with the exchange of material goods and food items (eg, Turnbull Reference Turnbull1965), as might have occurred with a dual population model for Neolithic western Scotland. Ahedo et al. (Reference Ahedo, Zurro, Caro and Galan2021) found that mixed farming-foraging economies constitute 25% of 1290 societies documented in the Ethnographic Atlas, the majority of which also contained a fishing component. Such mixed economies are ethnographically well documented in south-east Asia (Barton Reference Barton, Cummings, Jordan and Zvelebil2014) and North America (Spielmann Reference Spielmann, Cummings, Jordan and Zvelebil2014), where clear-cut dichotomies between farmers and foragers are rare and it is common for groups to switch between a predominance of hunting and gathering to agriculture, and then back again.