Quantifying ocular morphologies in extant primates for reliable interspecific comparisons

García, Juan Olvido Perea

doi:10.1093/jole/lzw004

Cited by 12 publications

(35 citation statements)

References 22 publications

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“…The observation that all 3 species present conspicuous eye coloration suggests reliance on gaze cues was relevant to our last common ancestor (LCA), and may date to the LCA of all extant great apes, with differential patterns of scleral depigmentation reported in gorillas (5) and orangutans (6). We do not know the ancestral state of scleral pigmentation, so we can only speculate about why bonobos and humans take a different route to conspicuous eye color than chimpanzees.…”

Section: Discussionmentioning

confidence: 99%

“…Similarly, if the genetic underpinnings of variation in scleral pigmentation are a by-product of selection against aggression, these should correspond to genes that affect migration of NCC in embryogenesis. These methods could be applied to test whether selection against aggression underlies speciation between extant species of apes: Lowland gorillas display lighter sclerae than mountain gorillas (5), and Sumatran display lighter sclerae than Bornean orangutans (6).…”

Section: Discussionmentioning

confidence: 99%

“…We followed the procedure in ref. 6 but further specified our sampling area: The selection extended from the pupil and two-thirds the length of the iris radius into the sclera. The height was up to 10% of the total iris diameter.…”

Section: Methodsmentioning

confidence: 99%

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Scleral pigmentation leads to conspicuous, not cryptic, eye morphology in chimpanzees

García

Kret

Monteiro

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

111

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Gaze following has been argued to be uniquely human, facilitated by our depigmented, white sclera [M. Tomasello, B. Hare, H. Lehmann, J. Call, J. Hum. Evol. 52, 314–320 (2007)]—the pale area around the colored iris—and to underpin human-specific behaviors such as language. Today, we know that great apes show diverse patterns of scleral coloration [J. A. Mayhew, J. C. Gómez, Am. J. Primatol. 77, 869–877 (2015); J. O. Perea García, T. Grenzner, G. Hešková, P. Mitkidis, Commun. Integr. Biol. 10, e1264545 (2016)]. We compare scleral coloration and its relative contrast with the iris in bonobos, chimpanzees, and humans. Like humans, bonobos’ sclerae are lighter relative to the color of their irises; chimpanzee sclerae are darker than their irises. The relative contrast between the sclera and iris in all 3 species is comparable, suggesting a perceptual mechanism to explain recent evidence that nonhuman great apes also rely on gaze as a social cue.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Scleral pigmentation leads to conspicuous, not cryptic, eye morphology in chimpanzees

García

Kret

Monteiro

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

111

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“…In Western gorillas (Gorilla gorilla) and bonobos (Pan paniscus), scleral pigmentation appears to be particularly plastic, ranging from plain black to fully white (Mayhew & Gómez, 2015;Perea García et al, 2019). A small-scale study also found predominantly light sclerae in Sumatran orangutans (Pongo abelii) (Perea García, 2016). Bornean orangutans (Pongo pygmaeus), chimpanzees (Pan troglodytes) and Eastern gorillas (Gorilla beringei) were instead reported to almost consistently display dark sclerae (Mayhew & Gómez, 2015;Perea García, 2016;Perea García et al, 2019; but see e.g., Goodall, 1986) for exceptions), so that great ape scleral coloration does not appear to follow a clear phylogenetic pattern.…”

Section: Introductionmentioning

confidence: 98%

“…As described above, it has been argued that eye coloration in the genera Homo and Pan represents an adaptation for optimized glance cueing (Perea García et al, 2019) and that ocular coloration is tightly correlated with sociocognitive functions among great apes and humans (Kobayashi & Kohshima, 2001;Tomasello et al, 2007;Perea García, 2016). This notion implies that primates that are not expected to utilize glance cues should show less conspicuous ocular contrasts, representing an ancestral state compared to the optimized patterns (Perea García, 2016). Gibbon eyes indeed appear unspecialized based on a small mixed-species dataset presented by Kobayashi and Kohshima (2001).…”

Section: Introductionmentioning

confidence: 99%

Ocular pigmentation in humans, great apes, and gibbons is not suggestive of communicative functions - having an eye on the ‘cooperative eye hypothesis’

Caspar

Biggemann

Geissmann

et al. 2021

Preprint

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Pigmentation patterns of the visible part of the eyeball, encompassing the iris and portions of the sclera, have been discussed to be linked to social cognition in primates. In the context of the cooperative eye hypothesis, the white sclera of humans has been viewed as a derived adaptive trait, enhancing communication via glance cueing. Here, we provide a comparative analysis of ocular pigmentation patterns in 15 species of hominoids (humans, great apes & gibbons) representing all extant ape genera, based on photographs and literature data. Additionally, we quantify hominoid scleral exposure on the genus level during different glancing situations. Our data reveals a continuum of eye pigmentation traits among the studied taxa. Gibbons display darker, more uniformly colored eyes than great apes and expose less sclera, particularly during averted glancing. Iridoscleral contrasts in orangutans and gorillas approach the human condition but differ between congeneric species. Contrary to recent discussions, we found chimpanzee eyes to exhibit a cryptic coloration scheme that resembles gibbons more than other great apes and that does not enhance glance cueing or gaze following. We critically evaluate the evidence for links between social cognition and eye pigmentation in primates, concluding that the cooperative eye hypothesis cannot convincingly explain the patterns observed. Although the human eye exhibits unique traits that are likely linked to social communication, high iridoscleral contrast is not one of them. Differences in scleral pigmentation between great apes and humans are gradual and might have arisen via genetic drift and sexual selection.

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White sclera is present in chimpanzees and other mammals

Clark

Lee

Poux

et al. 2023

Journal of Human Evolution

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Quantifying ocular morphologies in extant primates for reliable interspecific comparisons

Cited by 12 publications

References 22 publications

Scleral pigmentation leads to conspicuous, not cryptic, eye morphology in chimpanzees

Scleral pigmentation leads to conspicuous, not cryptic, eye morphology in chimpanzees

Ocular pigmentation in humans, great apes, and gibbons is not suggestive of communicative functions - having an eye on the ‘cooperative eye hypothesis’

White sclera is present in chimpanzees and other mammals

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