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Perea-García JO, Teuben A, Caspar KR. Look past the cooperative eye hypothesis: reconsidering the evolution of human eye appearance. Biol Rev Camb Philos Soc 2025. [PMID: 40366110 DOI: 10.1111/brv.70033] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2024] [Revised: 04/24/2025] [Accepted: 04/28/2025] [Indexed: 05/15/2025]
Abstract
The external appearance of the human eye has been prominently linked to the evolution of complex sociocognitive functions in our species. The cooperative eye hypothesis (CEH) proposes that human eyeballs, with their weakly expressed conjunctival and scleral pigmentation, are uniquely conspicuous and evolved under selective pressures to behave cooperatively, therefore signalling attentiveness to conspecifics. Non-human primates are instead assumed to display less-salient eye morphologies that help mask their gaze to facilitate competitive, rather than cooperative actions. Here, we argue that the CEH, although continuing to be influential, lacks robust empirical support. Over the past two decades, multidisciplinary research has undermined its original rationale and central premises: human eye pigmentation does not uniquely stand out among primates, it is not uniform at species level and the available evidence does not conclusively suggest that it facilitates gaze following to notable extents. Hence, the CEH currently provides a theoretical framework that risks confusing, rather than informing, inferences about the evolution of human external eye appearance and its selective drivers. In a call to move past it, we review alternative hypotheses with the potential to elucidate the emergence of the human ocular phenotype from the considerable spectrum of diversity found within the primate order.
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Affiliation(s)
- Juan Olvido Perea-García
- Center for Language Evolution Studies, Nicolaus Copernicus University in Toruń, Fosa Staromiejska 3, Toruń, 87-100, Poland
- University Institute for Health and Biomedical Research (IUIBS), Universidad Las Palmas de Gran Canaria, Las Palmas, Spain
| | - Aurora Teuben
- University of Amsterdam, Science Park 904, Amsterdam, 1098 XH, The Netherlands
| | - Kai R Caspar
- Institute of Cell Biology, Heinrich Heine University Düsseldorf, Universitätsstr. 1, Düsseldorf, D-40225, Germany
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Agnifili L, Palamini A, Brescia L, Porreca A, Oddone F, Tanga L, Ruggeri ML, Quarta A, Mastropasqua R, Di Nicola M, Mastropasqua L. Uveoscleral Outflow Routes after MicroPulse Laser Therapy for Refractory Glaucoma: An Optical Coherence Tomography Study of the Sclera. Int J Mol Sci 2024; 25:5913. [PMID: 38892100 PMCID: PMC11172512 DOI: 10.3390/ijms25115913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2024] [Revised: 05/21/2024] [Accepted: 05/26/2024] [Indexed: 06/21/2024] Open
Abstract
To analyze in vivo scleral changes induced by MicroPulse transscleral laser therapy (MP-TLT) in refractory glaucoma using anterior segment-optical coherence tomography (AS-OCT). Forty-two candidate patients for MP-TLT were consecutively enrolled and underwent AS-OCT at baseline and after six months. MP-TLT success was defined as an intraocular pressure (IOP) reduction by one-third. The main outcome measures were the mean superior (S-), inferior (I-), and total (T-) intra-scleral hypo-reflective space area (MISHA: mm2) and scleral reflectivity (S-SR, I-SR, T-SR; arbitrary scale) as in vivo biomarkers of uveoscleral aqueous humor (AH) outflow. The IOP was the secondary outcome. The relations between the baseline-to-six months differences (D) of DS-MISHA, DI-MISHA, and DT-MISHA and DS-SR, DI-SR, DT-SR, and DIOP, were investigated. At 6 months, the median IOP reduction was 21% in the failures and 38% in the successes. The baseline S-MISHA, I-MISHA, and T-MISHA did not differ between the groups, while S-SR and T-SR were higher in the successes (p < 0.05). At six months, successful and failed MP-TLTs showed a 50% increase in S-MISHA (p < 0.001; p = 0.037), whereas I-SR and T-SR reduced only in the successes (p = 0.002; p = 0.001). When comparing DS-MISHA, DI-MISHA, and DT-MISHA and DS-SR, DI-SR, and DT-SR, there were no significant differences between the groups. In the successful procedures, DIOP was positively correlated with DT-MISHA and DI-MISHA (ρ = 0.438 and ρ = 0.490; p < 0.05). MP-TLT produced potentially advantageous modifications of the sclera in refractory glaucoma. Given the partial correlation between these modifications and post-treatment IOP reduction, our study confirmed that the activation of the uveoscleral AH outflow route could significantly contribute to the IOP lowering after MP-TLT.
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Affiliation(s)
- Luca Agnifili
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
| | - Andrea Palamini
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
| | - Lorenza Brescia
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
| | - Annamaria Porreca
- Laboratory of Biostatistics, Department of Medical, Oral and Biotechnological Sciences, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy; (A.P.)
| | | | - Lucia Tanga
- IRCCS Fondazione Bietti, Via Livenza, 3, 00198 Rome, Italy
| | - Maria Ludovica Ruggeri
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
| | - Alberto Quarta
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
| | - Rodolfo Mastropasqua
- Department of Neuroscience, Imaging and Clinical Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy
| | - Marta Di Nicola
- Laboratory of Biostatistics, Department of Medical, Oral and Biotechnological Sciences, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy; (A.P.)
| | - Leonardo Mastropasqua
- Ophthalmology Clinic, Department of Medicine and Ageing Science, “G. d’Annunzio” University Chieti-Pescara, 66100 Chieti, Italy (L.B.)
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Wacewicz S, Perea-García JO, Lewandowski Z, Danel DP. The adaptive significance of human scleral brightness: an experimental study. Sci Rep 2022; 12:20261. [PMID: 36424405 PMCID: PMC9691750 DOI: 10.1038/s41598-022-24403-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Accepted: 11/15/2022] [Indexed: 11/27/2022] Open
Abstract
Homogeneously depigmented sclerae have long been proposed to be uniquely human-an adaptation to enable cooperative behaviour by facilitating interpersonal coordination through gaze following. However, recent evidence has shown that deeply pigmented sclerae also afford gaze following if surrounding a bright iris. Furthermore, while current scleral depigmentation is clearly adaptive in modern humans, it is less clear how the evolutionarily intermediate stages of scleral pigmentation may have been adaptive. In sum, it is unclear why scleral depigmentation became the norm in humans, while not so in sister species like chimpanzees, or why some extant species display intermediate degrees of pigmentation (as our ancestors presumably did at some point). We created realistic facial images of 20 individually distinct hominins with diverse facial morphologies, each face in the (i) humanlike bright sclera and (ii) generalised apelike dark sclera version. Participants in two online studies rated the bright-sclera hominins as younger, healthier, more attractive and trustworthy, but less aggressive than the dark-sclera hominins. Our results support the idea that the appearance of more depigmented sclerae promoted perceived traits that fostered trust, increasing fitness for those individuals and resulting in depigmentation as a fixed trait in extant humans.
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Affiliation(s)
- Slawomir Wacewicz
- Center for Language Evolution Studies, Nicolaus Copernicus University, Toruń, Poland.
| | - Juan Olvido Perea-García
- The Cognitive Psychology Unit, Faculty of Social Sciences, Leiden University, Leiden, The Netherlands
| | - Zdzisław Lewandowski
- Department of Human Biology, Wroclaw University of Health and Sport Sciences, Wroclaw, Poland
| | - Dariusz P Danel
- Department of Anthropology, Hirszfeld Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, Wroclaw, Poland
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