Morphological and population genomic evidence that human faces have evolved to signal individual identity.

Facial recognition plays a key role in human interactions, and there has been great interest in understanding the evolution of human abilities for individual recognition and tracking social relationships. Individual recognition requires sufficient cognitive abilities and phenotypic diversity within a population for discrimination to be possible. Despite the importance of facial recognition in humans, the evolution of facial identity has received little attention. Here we demonstrate that faces evolved to signal individual identity under negative frequency-dependent selection. Faces show elevated phenotypic variation and lower between-trait correlations compared with other traits. Regions surrounding face-associated single nucleotide polymorphisms show elevated diversity consistent with frequency-dependent selection. Genetic variation maintained by identity signalling tends to be shared across populations and, for some loci, predates the origin of Homo sapiens. Studies of human social evolution tend to emphasize cognitive adaptations, but we show that social evolution has shaped patterns of human phenotypic and genetic diversity as well

Programming human cell fate: overcoming challenges and unlocking potential through technological breakthroughs

In recent years, there have been notable advancements in the ability to programme human cell identity, enabling us to design and manipulate cell function in a Petri dish. However, current protocols for generating target cell types often lack efficiency and precision, resulting in engineered cells that do not fully replicate the desired identity or functional output. This applies to different methods of cell programming, which face similar challenges that hinder progress and delay the achievement of a more favourable outcome. However, recent technological and analytical breakthroughs have provided us with unprecedented opportunities to advance the way we programme cell fate. The Company of Biologists’ 2023 workshop on ‘Novel Technologies for Programming Human Cell Fate’ brought together experts in human cell fate engineering and experts in single-cell genomics, manipulation and characterisation of cells on a single (sub)cellular level. Here, we summarise the main points that emerged during the workshop's themed discussions. Furthermore, we provide specific examples highlighting the current state of the field as well as its trajectory, offering insights into the potential outcomes resulting from the application of these breakthrough technologies in precisely engineering the identity and function of clinically valuable human cells

Single-Unit Responses Selective for Whole Faces in the Human Amygdala

The human amygdala is critical for social cognition from faces, as borne out by impairments in recognizing facial emotion following amygdala lesions and differential activation of the amygdala by faces. Single-unit recordings in the primate amygdala have documented responses selective for faces, their identity, or emotional expression, yet how the amygdala represents face information remains unknown. Does it encode specific features of faces that are particularly critical for recognizing emotions (such as the eyes), or does it encode the whole face, a level of representation that might be the proximal substrate for subsequent social cognition? We investigated this question by recording from over 200 single neurons in the amygdalae of seven neurosurgical patients with implanted depth electrodes. We found that approximately half of all neurons responded to faces or parts of faces. Approximately 20% of all neurons responded selectively only to the whole face. Although responding most to whole faces, these neurons paradoxically responded more when only a small part of the face was shown compared to when almost the entire face was shown. We suggest that the human amygdala plays a predominant role in representing global information about faces, possibly achieved through inhibition between individual facial features

Two of the Same? Infants\u27 Conceptual Representation of Faces Based Upon Gender, Race, and Kind Information

Infants’ perceptual abilities allow them to distinguish faces of different races and genders from an early age (for a review, see Pascalis et al., 2011). However, it is still unknown when infants begin using these perceptual differences to represent faces in a conceptual, kind-based manner. The current dissertation examined this issue by testing whether 12- and 24-month-old infants represent faces of different races and genders as distinct ‘kinds’ or instead as variations of a single broader category (e.g., ‘human face’). The current dissertation included two experiments each with a different type of violation-of-expectation individuation paradigm. Experiment 1 used a passive viewing looking-time measure to establish infants’ baseline response to human- vs. non-human faces as well as their response to male versus female faces. Results from Experiment 1 replicated previous looking time measures and found evidence that 12-month-old infants have a representation for an ontological or ‘human’ kind. Using a manual search paradigm, infants’ face individuation based on gender and race was assessed in Experiment 2. Twenty-four-month-old infants, but not younger infants, displayed reaching behaviors that indicated they individuated faces based on the kind ‘human’ as well as face gender. There was no evidence of individuation based on a face’s race group. The current findings help to determine how infants begin to conceptually represent gender and race differences as identity-defining variations that might serve as a starting point for socio-cognitive biases observed later in development

Role of Temporal Processing Stages by Inferior Temporal Neurons in Facial Recognition

In this review, we focus on the role of temporal stages of encoded facial information in the visual system, which might enable the efficient determination of species, identity, and expression. Facial recognition is an important function of our brain and is known to be processed in the ventral visual pathway, where visual signals are processed through areas V1, V2, V4, and the inferior temporal (IT) cortex. In the IT cortex, neurons show selective responses to complex visual images such as faces, and at each stage along the pathway the stimulus selectivity of the neural responses becomes sharper, particularly in the later portion of the responses. In the IT cortex of the monkey, facial information is represented by different temporal stages of neural responses, as shown in our previous study: the initial transient response of face-responsive neurons represents information about global categories, i.e., human vs. monkey vs. simple shapes, whilst the later portion of these responses represents information about detailed facial categories, i.e., expression and/or identity. This suggests that the temporal stages of the neuronal firing pattern play an important role in the coding of visual stimuli, including faces. This type of coding may be a plausible mechanism underlying the temporal dynamics of recognition, including the process of detection/categorization followed by the identification of objects. Recent single-unit studies in monkeys have also provided evidence consistent with the important role of the temporal stages of encoded facial information. For example, view-invariant facial identity information is represented in the response at a later period within a region of face-selective neurons. Consistent with these findings, temporally modulated neural activity has also been observed in human studies. These results suggest a close correlation between the temporal processing stages of facial information by IT neurons and the temporal dynamics of face recognition

The role of attention in face processing

Selective attention is widely regarded as a crucial component of human perception. In the visual domain, attentional mechanisms have been implicated in stimulus encoding, implicit recognition, conscious perception and goal-directed behaviour. To date, however, the role of attention in face processing has been largely overlooked. This is remarkable given the social and biological importance of faces, and the wealth of psychological research that has focused on faces as stimuli. Moreover, if we are to better understand how the human brain processes faces, then this would also require an insight into the interaction between attention and face processing. The experiments in this thesis addressed the relation of attention and face processing directly by assessing the consequences of various attentional manipulations in response-competition and repetition priming tasks. The first line of enquiry examined observers’ ability to attend selectively to facial expression and identity, and whether attention is required for the integration of these types of information into a multi-dimensional face percept. Subsequent experiments examined capacity limits in face processing and attention biases to faces and nonface comparisons. The main findings indicated that face processing is capacity limited, such that only a single face can be processed at a time, and that faces are particularly efficient at retaining and engaging visual attention in comparison to nonface objects. However, while face processing limits appear to proceed independent of a general capacity, attention biases to faces may reflect processing stages that are shared with other stimuli. These findings are discussed in relation to existing research on faces and attention