Psychology: Portraits help track historical changes in trustworthiness

Facial displays that convey trustworthiness in European portraits increased from 1500–2000 and are suggestive of shifts in social trust, reports a study in Nature Communications. The findings, obtained using a face-processing algorithm, also suggest that the rise in trustworthiness displays (based on an analysis of facial muscle contractions) was associated with improving living standards over the period.

Social trust is associated with positive societal outcomes, including improved economic performance and lower crime rates. However, the origins of trust are unclear, partly because changes in social trust are difficult to quantitatively document over time.

To track historical changes in trustworthiness, Nicolas Baumard and colleagues designed an algorithm to generate trustworthiness evaluations of portraits. The validity of the algorithm was first tested using photographs of faces where trustworthiness had been rated by human participants. In further tests, the algorithm reproduced findings on perceived trustworthiness from the scientific literature based on factors including age, gender and emotion displayed.

By analysing a collection of 1,962 English portraits from the National Portrait Gallery in London from 1506–2016, the authors found a significant increase in trustworthiness displays over time. They were also able to replicate their findings in 4,106 portraits from the Web Gallery of Art, spanning 19 Western European countries from 1360–1918.

In line with the assumption that increased trustworthiness in portraits reflects changes in social trust, the algorithm was applied to 2,277 selfies on social media from six cities. Here, increased displays of trustworthiness were observed in images from cities where interpersonal trust and cooperation had been assessed as being higher in the European and World Value surveys.

Looking at potential influences on the rise in trustworthiness displays over the period, Baumard and co-authors found that this shift was more strongly associated with rises in GDP per capita than institutional change (for example, the rise of more democratic institutions).