Researchers at Cambridge University, U.K. finds that after agriculture’s emergence in Central Europe starting around 5300 BC, bones of those living in the Danube River valley became progressively less strong, pointing to a regressive decline in human mobility and loading.
The scientists observe that human bones are remarkably adaptable and respond surprisingly quickly to change. When under stress through physical exertion – such as long-distance walking or running – bones gain in strength as fibres are added or redistributed according to where stress is are highest. This ability of bone to adapt to loading is shown by analysis of skeletons of modern athletes, whose bones show remarkably rapid adaptation to both the intensity and direction of strains.
Because the structure of human bones can inform us about the lifestyles of the individuals they belong to, they can also provide valuable clues for biological anthropologists investigating past cultures. Research by Alison Macintosh, a PhD candidate in Cambridge University’s Department of Archaeology and Anthropology, finds functional adaptation in postcranial skeletal morphology in response to prolonged cultural and behavioural change across ~6150 years of agriculture in Central Europe (~5300 cal BC to 850 AD). Ms. Macintosh has investigated changes in upper limb manipulative behaviour, lower limb loading, and mobility using engineering-based estimates of mechanical performance (cross-sectional geometric properties and shape indices) derived from 3D laser scans and silicone moulds. She has also examined distribution and integration of plasticity to mechanical loading within and between the limbs. Ms. Macintosh’s research at Cambridge is affiliated with the ERC-funded project: “From the earliest modern humans to the onset of farming (45,000-4,500 BP)”.
That study’s principal investigator – Dr. Ron Pinhasi of the University College in Dublin, Ireland, notes that colonization of Europe by anatomically modern humans (AMHs) ca. 45,000 years before present (BP) and the transition to farming ca. 8,000 BP were two pivotal events in human prehistory. Both of these developments involved certain cultural and biological adaptations, technological innovations, and behavioural plasticity that are unique to our species.
Dr. Pinhasi notes that reconstruction of these processes and the causality between them has so far remained elusive due to technological, methodological and logistical complexities, and the study investigates the complex intertwined interface among morphological, genetic, behavioural, and cultural factors that shaped the population history of European AMHs. The approach taken includes (a) the collection of bioarchaeological, aDNA, stable isotope (for the analysis of ancient diet) and radiometric data on 500 skeletons from key sites/phases in Europe and western Anatolia, and (b) the application of existing and novel aDNA, bioarchaeological and simulation methodologies.
Ms. Macintosh will present some of her research results at the 83rd Annual Meeting of the American Association of Physical Anthropologists at Calgary, Alberta, running 8-12 April, 2014. In her presentation, entitled “Femoral and tibial morphology reflects complex change in sex roles, mobility and division of labour across ~6200 years of agriculture in Central Europe,” She will show that mobility and lower limb loading in male agriculturalists declined progressively and consistently through time and were more significantly affected by culture change in Central Europe than they were in females.
The presentation will draw on work published by biological anthropologist Dr. Colin Shaw (of the University of Cambridge McDonald Institute for Archaeological Research that has enabled Ms. Macintosh to interpret this male decline in relation to present day Cambridge University students.
Ms. Macintosh’s primary research focus is hominin skeletal morphology, and in particular post-cranial variation, and she says she is interested in reconstructing prehistoric activity patterns by determining how morphology reflects adaptation. She employs a unique approach that utilizes 1) traditional in-vitro analyses of skeletal and fossil hominin remains, 2) non-traditional in-vivo analyses that assesses skeletal and soft tissue variation in living humans and, 3) human physiological experimentation aimed at defining the effect of prehistoric activity patterns on morphology. The research requires application of advanced analytical techniques, including high-resolution 3D imaging and experimental archaeology.
Robust To Sedentary
Using Dr. Shaw’s study of bone rigidity among modern Cambridge University undergraduates, Ms. Macintosh suggests that male mobility among primitive farmers (around 7,300 years ago) was, on average, at a level near that of student cross-country runners in 2014, observing that within just over 3,000 years, average human mobility had dropped to the level approximating that of students categorized as sedentary today, after which the decline slowed.
“Long-term biomechanical analyses of bones following the transition to farming in Central Europe haven’t been carried out,” says Ms. Macintosh in a Cambridge U. release. “But elsewhere in the world they show regional variability in trends. Sometimes mobility increases, sometimes it declines, depending on culture and environmental context. After the transition to farming, cultural change was prolonged and its pace was rapid. My research in Central Europe explores whether – and how – this long term pressure continued to drive adaptation in bones.”
Noting that archaeological evidence has shown that gradual intensification of agriculture was accompanied by rising production and complexity of metal goods, technological innovation and the extension of trade and exchange networks, Ms. Macintosh says “These developments are likely to have brought about changes in divisions of labour by sex and socioeconomic organisation as men and women began to specialize in certain tasks and activities – such as metalworking, pottery, crop production, tending and rearing livestock…. I’m interested in how the skeleton adapted to people’s specific behaviours during life, and how this adaptation can be used to reconstruct long-term changes in behaviour and mobility patterns with cultural diversification, technological innovation, and increasingly more complex and stratified societies since the advent of farming.”
Gradual Loss Of Mobility
As a means of tracking changes in the structure of bones over time, Ms. Macintosh laser-scanned skeletons found in cemeteries across Central Europe, concentrating in particular on an analysis of engineering-based cross-sectional geometric properties as measures of the loading imposed on the lower limb bones during life. Her research took her to sites in Germany, Hungary, Austria, the Czech Republic and Serbia. The earliest skeletons she examined dated from around 5300 BC with the most recent from around 850 AD – a time span of 6,150 years.
Using a portable desktop 3D laser surface scanner to scan femora and tibiae, she found that male tibiae became less rigid and bones in both males and females became less strengthened to loads in one direction more than another, such as front-to-back in walking. These findings all indicate a drop in mobility. In other words, she deduces that it is likely the people to whom the skeletons belonged became, over generations, less intensely active and probably covered less distance, or carried out less physically demanding tasks, than preceding generations.
“Both sexes exhibited a decline in anteroposterior, or front-to-back, strengthening of the femur and tibia through time, while the ability of male tibiae to resist bending, twisting, and compression declined as well,” says Ms/ Macintosh, “My results suggest that, following the transition to agriculture in Central Europe, males were more affected than females by cultural and technological changes that reduced the need for long-distance travel or heavy physical work. This also means that, as people began to specialize in tasks other than just farming and food production, such as metalworking, fewer people were regularly doing tasks that were very strenuous on their legs.”
Female Multitasking A Factor
Although there was some evidence for declining mobility in females as well, trends were inconsistent through time in most properties. Macintosh believes this variation may indicate that women in early farming cultures performed a great variety of tasks – multi-tasking, as it were – or at least undertook fewer tasks requiring significant lower limb loading. Ms. Macintosh notes that there is evidence from two of the earliest cemeteries she studied that females were using their teeth in processing activities to carry out tasks unlikely to have loaded their lower limbs much.
The Cambridge release notes that interesting comparisons can be made between archaeological evidence from Central European skeletons dating from around 7,300-1,150 years ago and data from modern farming populations elsewhere in the world, citing a study by Panter-Brick in 1996 that found relative workload (as exhibited by time allocation and energy expenditure) between males and females in modern farming populations is much more variable than in foraging groups. As in early Central European farming communities, higher physical activity is recorded among males than females in Indian and Nepalese farming communities, but females have a higher relative workload than males in farming communities in the Upper Volta and the Gambia.
“This variability in the sexual division of labour in living agro-pastoralist groups shows the importance of context, ecology, and various cultural factors on sex differences in physical activity. So it is important when studying long-term trends in behavioural change between the sexes that the geographic region is kept small, to help control for some of this variability,” says Ms. Macintosh, who points to female skeletons showing a major change in femoral bending and torsional rigidity from the Bronze Age into the Iron Age – between about 1450 BC and 850 BC in the samples studied – when women had the strongest femora of all the females examined in the study. She suggests that this could be because the Iron Age sample included skeletons of Hungarian Scythians, a group for whom large animal husbandry, horsemanship and archery were particularly important, and Scythian females are thought to have performed heavy physical work and were known to participate in combat.
“However, if this high Iron Age female bone strength in the femur was due to high mobility, it would also probably be visible in the tibia as well, which it was not. In that case, it could be something other than mobility that is driving this Iron Age female bone strength, possibly a difference in body size or genetics,” comments Ms. Macintosh, observing that because the skeleton holds a record of the loading it experiences during life, it can provide important clues as to the behaviour of past people through prolonged cultural change, and concluding that overall, during the first 6,150 years of farming in Central Europe prosperity generated by intensive agriculture drove socioeconomic change and allowed people to specialize in tasks other than food production.
“In Central Europe, adaptations in human leg bones spanning this time frame show that it was initially men who were performing the majority of high-mobility tasks, probably associated with tending crops and livestock,” Ms. Macintosh notes. “But with task specialization, as more and more people began doing a wider variety of crafts and behaviours, fewer people needed to be highly mobile, and with technological innovation, physically strenuous tasks were likely made easier. The overall result is a reduction in mobility of the population as a whole, accompanied by a reduction in the strength of the lower limb bones.”
University College Dublin
University College Dublin