Filling, color, and shape: individuality in chimpanzee drawings.

Understanding the origins of drawing in humans requires studying the drawing behavior of our closest relatives, the great apes. This study examines the drawing behavior of chimpanzees to assess cognitive abilities in a long-term context. Our systematic analysis of previously unseen and newly documented drawings from six chimpanzees over several years revealed significant inter- and intra-individual differences, as well as seasonal variation. Chimpanzees used multiple colors, but no specific color preferences were observed. Although they use their right hand more, they can use both hands to produce a single drawing. Using Principal Component Analysis (PCA), we identified three graphically significant dimensions: filling aspect, color aspect and shape aspect, suggesting that the measures were meaningfully or intentionally regrouped. Drawing style varied between seasons, but more importantly between individuals, with each chimpanzee exhibiting a kind of unique drawing personality. In addition, changes in drawing style were observed over the years, suggesting a development in individual drawing behavior. Comparisons with previous studies on orangutans and human children suggest that chimpanzee drawing may reflect personality traits and common cognitive abilities. These findings add to our understanding of the evolutionary origins of human artistic expression.