Being left-handed and dyslexic, the first area of the brain that interested me, long ago, was Broca’s area. The theory that has been around for some time in various forms – that the evolution of language is connected to the evolution of fine motor skills with the hands – has intrigued me. A recent paper gives some evidence for the co-evolution of language and complex tool knapping (see citation below).
Knapping stone is not something that can be done in a scanner. The researchers used functional transcranial Doppler ultrasonography (fTCD) to measure brain blood flow lateralization patterns. This method allow the subjects to move more or less naturally. Competent knappers made stone tools and did language exercises while the difference in blood flow between the two hemispheres was measured. The language test was cued word generation; a letter was given and the subject generated a string of words beginning with that letter. The tool making was the production of Acheulean tools, an early but sophisticated style of knapping. They found a similarity in the blood flow pattern in the two tasks during the first 10 seconds. After that the pattern diverged with the language task having more blood flow to the left hemisphere and the knapping task having more to the right. In both tasks the first few seconds are used to ‘set up’ or plan the activity.
“Our participants showed correlated LIs (lateralization indices ) during the initial 10 seconds after task onset for cued word generation and handaxe production. A number of previous studies have directly correlated LI values for different tasks and shown that tasks which draw on shared neural processing sites, such as the three language tasks described by Bishop, result in highly correlated LI measures. In contrast, cognitive tasks that draw on disparate brain areas, such as language and visuo-spatial tasks like driving, visual attention, or visual memory, lead to uncorrelated LIs. Since Acheulean stone knapping is a highly visuo-spatial task , our finding of a correlation between knapping and language requires explanation.
Making an Acheulean handaxe requires both working memory and planning memory. This careful planning is dominant in the initial phase of each experimental block in our study. This action planning draws on brain areas that are shared with language tasks, such as the left-lateralized ventral premotor areas and Broca’s area. Our subject pool shows highly correlated individual brain blood flow lateralization in the early phases of task execution for both tasks. Our findings add empirical data to the hypothesis that action planning for tool-making and language draw on shared functional brain structures. The correlated time-signatures for Acheulean knapping and language, which remain significantly correlated within subjects despite variability between subjects, indicates that the same brain networks are being activated for both tasks. They suggest that tool-making and language share a basis in more general human capacities for complex, goal-directed action. ”
If tool making and language co-evolved then this says something about the age of language.
“… the network for complex action planning might have emerged in human evolution as part of our brain size increase and reorganization, leading to both language and tool-making . We suggest the start of the Acheulean techno-complex at 1.75 million years ago as a likely candidate for this because Acheulean knapping required more complex action planning than Oldowan technologies.”
This is not a new idea. There is an interesting paper by Greenfield (see citation below) from 12 years ago. Here is the abstract:
During the first two years of human life a common neural substrate (roughly Broca’s area) underlies the hierarchical organization of elements in the development of speech as well as the capacity to combine objects manually, including tool use. Subsequent cortical differentiation, beginning at age two, creates distinct, relatively modularized capacities for linguistic grammar and more complex combination of objects. An evolutionary homologue of the neural substrate for language production and manual action is hypothesized to have provided a foundation for the evolution of language before the divergence of the hominids and the great apes. Support comes from the discovery of a Broca’s area homologue and related neural circuits in contemporary primates. In addition, chimpanzees have an identical constraint on hierarchical complexity in both tool use and symbol combination. Their performance matches that of the two-year-old child who has not yet developed the neural circuits for complex grammar and complex manual combination of objects.
This points to a very long history for the development of language. Current estimates for the start of language vary from almost 2 million years ago to 50,000. The 50,000 figure is often quoted but is probably no longer accepted by most Evolutionary Biologists but only by ‘one-mighty-leap’ theorists.
Uomini NT, & Meyer GF (2013). Shared Brain Laterialization Patterns in Language and Acheulean Stone Tool Production: A Functional Transcranial Doppler Ultrasound Study. PLoS ONE, 8 (8) : 10.1371/journal.pone.0072693
Greenfield PM (1991). Language, tools and brain: the ontogeny and phylogeny of hierachically organized sequential behavior. Behavior & Brain Sciences, 14, 531-595