Friday, October 6, 2017

The ratio of left-handed people in hunter-gatherer societies has been maintained since Prehistory

In her thesis Eder Domínguez has studied handedness by analysing the lithic industry

In her thesis Eder Dominguez-Ballesteros, who holds an international PhD from the UPV/EHU-University of the Basque Country, has explored the handedness of prehistoric populations through the lithic industry. The thesis of this researcher in the UPV/EHU's Department of Geography, Prehistory and Archaeology is entitled ‘Evaluación arqueológica del proceso de lateralización. Determinación cuantitativa de la lateralidad poblacional, desde los neandertales hasta la actualidad' [Archaeological evaluation of the handedness process. Quantitative determination of population handedness from the Neanderthals to the present day]. It was supervised by the lecturers Álvaro Arrizabalaga of the above-mentioned department, and Ignacio Martínez of the University of Alcalá de Henares.

"Prehistoric tools," explains Eder Dominguez, "provide a source of very valuable information to find out what the life of our ancestors was like, and also to understand how they behaved and how they thought. Due to the fact that it is the mind that creates the tool, we can try and obtain information about human cognition through the study of lithic industries". So the study of prehistoric tools can be completed with an analysis that includes ethological and cognitive approaches that will enable information, aside from that obtained from a purely typological study, to be extracted. Following this reasoning, the number of studies over the last few decades analysing the handedness of prehistoric populations through the lithic industry have been increasing.

Handedness is a quality exhibited by certain species and which involves assigning different roles to each side of the body whenever a specific task is carried out, by giving one of them greater dominance. "These studies endeavour to contribute information towards knowledge about cerebral asymmetries and the development of language during our evolution because they are strongly related to handedness," pointed out the new PhD holder.

The study carried out by this researcher has its starting point in the analysis of prehistoric societies of the Neolithic and Chalcolithic (producing societies), "which allow one to analyse how the cultural factors of population handedness exerted an influence" in order to go on studying societies made up of Neanderthals, already in the Palaeolithic (hunter-gatherer societies). She developed two methods to carry out this research. "The first one has enabled us to deduce the handedness of an axe maker from the morphology of the cut of a polished axe and which can be applied to Neolithic and Chalcolithic materials; the second has enabled us to establish the handedness of the carver by means of the flakes by analysing cracks that sometimes develop at the percussion point and are known as parabolic cracks. On the basis of these methods we have established the population levels of handedness at different moments of prehistory, and compared them with current population levels in various societies; this has allowed us to better understand cerebral asymmetries, how they evolved and how they relate to language," pointed out the UPV/EHU researcher.

Polished axes and flakes

For the Neolithic and Chalcolithic periods a large quantity of polished tools from various sites located in Bizkaia, Alava and Navarre were studied. The remains at a total of 36 sites were analysed (14 in Bizkaia, 21 in Álava and one in Navarre), and it was at the sites of the Urrunaga Reservoir in Legutiano (Álava), and of Pico Ramos in Muskiz (Bizkaia), where the highest number of prehistoric axes were studied (24 and 10, respectively). With regard to the Palaeolithic archaeological remains, the researcher Eder Dominguez analysed the Mousterian levels of Le Moustier shelter (40,000 years), and of the VII level of Grotte Vaufrey (about 200,000 years), as well as the complete sequence of the Axlor shelter (Dima, Bizkaia).

In the case of producing societies belonging to the Neolithic and Chalcolithic periods, 100 polished axes were studied, and in the hunter-gatherer societies of the Palaeolithic, 690 flakes (412 at Le Moustier, 28 at Grotte Vaufrey and 250 at Axlor) were analysed. The results obtained indicate that the "population levels of handedness for hunter-gatherer societies display a left-handed/right-handed ratio of 3/7, whereas in the producing societies they would be slightly more lateralized with a left-handed/right-handed ratio of 2.7/7.3, with a slightly higher proportion of right-handed people," she pointed out.

«The Neanderthals had a cerebral organisation capable of producing language»

These ratios are somewhat distanced from those of industrialised societies where the percentage of left-handed people ranges between 5% and 15% depending on the level of industrialisation. They are, however, similar to those of current hunter-gatherer societies. "Although there is genetic control of manual handedness, questions such as culture, the socioeconomic state or even sex and age exert a strong influence on the population levels and on the actual manual dominance of the individual. Even the type of task we use to measure it, its nature and its complexity, influences the direction and intensity of our manual dominance. So we have to cautiously compare the manual handedness of a prehistoric population with that of the current ones and exercise care when contrasting the tasks currently used to measure manual dominance (e.g. writing) with those that our ancestors were able to carry out," explained Dominguez.

So, on the basis of the levels of handedness detected in prehistoric societies made up of Neanderthals, "we can deduce that their brain organisation was adapted to the production of articulate speech. But even though the relationship between handedness and language is known, one cannot assert that the individuals in the settlements possessed language; the only thing that can be said is that evidence exists of a cerebral organisation capable of possessing it," explained Eder Dominguez.

In the future through the study of more archaeological levels this method would allow one to find out about the handedness of populations in the past and how they evolved across the Palaeolithic to understand how cerebral asymmetries have been evolving and provide information as to the origin and development of speech in our genus.