Multi domain sensory exploitation of visual signals in humans and its implications on the evolution of trichromacy in catarrhine primates

Current research

My research aims at the understanding of exactly which colours actually serve as signals in the domain of food recognition and evaluation, the domain of dominance and submission display and the domain of sexual signalling, and how they could have been taken over from one domain to another via sensory exploitation during evolution.
In cooperation with the Emmy Noether Research Group of Dr. Bernhard Fink, Elite University of Göttingen, Germany, I investigate which colours convey the signals proposed by current literature. I conduct interactive computer based experiments with humans and I analyse the regions of interest (ROIs) in different sorts of stimuli which convey colour signals with means of an Hi-Speed Eye-Tracker.

Analysis in CIELab colour space will reveal similarities and divergences in position and orientation of the colours which serve as signals in all three domains.

Scientific background

Food recognition and evaluation
The species of the catarrhine clade - old world monkeys, apes and humans - are the only ones within the mammals with routine trichromacy, i.e. their visual system operates with two colour channels instead of one: the blue-yellow and the red-green channel. Their neuronal systems have evolved to accurately spot young leaves or ripening fruit hidden in thick forest canopy. They readily assess ripeness, nutritive value and taste of their food over long distances. Furthermore, during evolution, once physiological or behavioural reactions of individuals to these colourful red-green signals were genetically fixed, they could be exploited in other domains than food recognition and evaluation.

Decoding emotional states
Catarrhine species live in groups of up to several hundred individuals. Social interaction is crucially based on the ability to properly assess the intentions and emotional state of others. The more sophisticated the group structure and interaction, the more accurate the communication between individuals must be. Emotional states are coded in behavioural but also in physiological signals. Before culturally biased signals like posture, facial expression, voice pitch etc., the universal signal of changing skin colouration had already evolved. The more complex the groups of a species, the more skin they reveal to others, ultimately ending up loosing all concealing body hair, as it was the case during human evolution. Reddening of skin is a signal in the domain of dominance and submission display and in the domain of sexual signalling.

Dominance and submission display
Dominant, aggressive individuals show high haemoglobin oxygen saturation of their blood, which makes their skin appear reddish, a straightforward signal which makes opponents back down and intuitively avoid conflict. This signal, enhanced by red ornaments, leads to fighters winning more often in the Olympics one on one fighting sports, when wearing red. In the submission context, facial blushing combined with defensive behaviour signals shame and embarrassment and triggers sympathy for the subjects.

Sexual signalling
The same physiological changes appear in females nearing ovulation, signalling their fertility. In this period women leave more skin visible. Additionally, sexual arousal is more easily triggered and red blush of flirtation and red flush of sexual excitation are more prevalent. While these physiological changes are more subtle in humans than in most apes, they are intuitively enhanced by women since the very first human cultures, using ochre body paint, and up to the most advanced societies today where they use a broad variety of coloured cloths and especially cosmetics like red lipstick, make up, rouge etc.