Robert the Bruce's skull size shows he had high IQ

In a paper featuring an irresistible mix of history and psychology, researchers have estimated Robert the Bruce's IQ from his skull size and concluded that he was a highly intelligent man.

Ian Deary and colleagues first established the relationship between IQ and skull size among 48 men (aged 71-76) living in Edinburgh. The researchers scanned the men's brains using MRI and had them complete the National Adult Reading Test, known to be strongly related to full IQ test performance and designed especially for use with older participants.

Consistent with past research showing that head size and brain volume correlate with IQ, the new analysis revealed that skull size was significantly related to the men's IQ.

Next, the researchers scanned and measured a plaster cast of Robert the Bruce's skull, as well as measuring its size with callipers (see image above). Extrapolating from the statistical relationship between skull size and IQ found among the Edinburgh participants, the researchers estimated that Robert the Bruce, with his larger than average skull, had an impressive IQ of about 128, and possibly higher.

This would make Robert Bruce of similar intelligence to other military leaders as estimated by Catharine Cox in 1926, including Cromwell with an estimated IQ of 135, Napoleon at 145 and Washington at 140.

Robert Bruce is famed for his defeat of a full English army led by Edward II at Bannockburn in 1314, as well as his later efforts to consolidate Scotland's international position, culminating with the declaration of Arbroath in 1320.

"The IQ estimate for Robert Bruce accords with his military, political and intellectual achievements, especially given the highly personal nature of kingship in the Mediaeval period," the researchers concluded.
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Deary, I.J., Ferguson, K.J. Bastin, M.E., Barrow, G.W.S., Reid, L.M., Seckl, J.R., Wardlaw, J.M. & MacLullich. (2007). Skull size and intelligence, and King Robert Bruce's IQ. Intelligence, 35, 519-525.

Image credit and copyright: Ian Deary.

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