Skin, eye and hair color in humans as gibbon descendants

Today’s post was inspired by
this YouTube video on human skin color emphasizing the traditional factors: UV intensity, sunburn, skin cancer and vitamin D production vs melanin production.

In Europeans alone hair color
also varies according to latitude. As everyone knows, primitive darker colors were retained in Southern populations while blondes and reds had their sprinkled genesis in Northern European populations.

In a deeper dive,
results recovered by the large reptile tree (LRT, 2324 taxa) indicate there is more to the story of skin and hair color than latitude and sun exposure. In the LRT a lineage of gibbons was ancestral to humans. Bipedal by convergence, australopithecines were not human ancestors.

Gibbon ontogeny plays a part in skin and hair color, according to species.
Gibbon sexual dimorphism influences hair color, according to species.

Hair = fur color, part 1
“All northern white-cheeked gibbon infants are born with blonde fur like their mothers. By age two, their coloration turns black. It is not until the offspring reaches sexual maturity at 5 to 7 years old that females will change back to blonde while males stay black.”

Hair = fur color, part 2
“Lar gibbons color is variable, not related to sex – very dark brown, black, red or light buff.”

Hair color changes like these (Fig 1) are not found in chimps and gorillas.
Skin color in chimps is variable.

Hair = fur color, part 3
Southern white-cheeked gibbon: “unweaned juveniles are a light brown, turning to black after weaning. Adult males remain black, but adult females are brown.”

Skin color
In gibbon newborns the skin color is a light buff, darkening to black during maturity (Fig 1). So every variation of human skin and hair color can be traced back to gibbons.

Nostril orientation and eyebrows in gibbons
In most gibbons (Fig 2) the nose is a small bump, the nares are small and lateral. In the East Bornean gray gibbon the nares are rotated to right angles with one another = 45º from horizontal, closer to the condition in humans -= ventrally open. Eyebrows are also present. Eye color is lighter.

Nostril orientation in great apes
Gorillas, chimps and orangutans have much larger and anteriorly-facing nares at the tip of a flat nose atop a jutting muzzle (Fig 3), unlike humans. Eyebrows are lacking.

These are questions I wondered about as wee child. Finally there are answers!

Achilles tendon
According to Aerts et al 2018: “The well-developed Achilles tendon in humans is generally interpreted as an adaptation for mechanical energy storage and reuse during cyclic locomotion. All other extant great apes have a short tendon and long-fibred triceps surae, which is thought to be beneficial for locomotion in a complex arboreal habitat as this morphology enables a large range of motion. Surprisingly, highly arboreal gibbons show a more human-like triceps surae with a long Achilles tendon.”

Earlier
we looked at several other traits that more closely link the gibbon line to the human line, including Homo floresiensies (Fig 5), which were found on the island of Flores (Fig 6) very close to the East Borneo environs of Hylobates funereus (Fig 2) and Java man, Homo erectus (Fig 5).

Maybe the universally accepted “out-of-Africa” hypothesis needs to be modified in light of these insights. Borneo and Flores have a few overlooked human ancestors, too.

When I wrote and Little Brown published
“From the Beginning – The Story of Human Evolution” it was widely accepted that humans branched off prior to the knuckle-walking clade of orangutans, chimps and gorillas. No one then thought that Australopithecus (Fig 5) was bipedal by convergence.

Let’s see where these observations and hypotheses take us.

References
Aerts P et al 2018. The gibbon’s Achilles tendon revisited: consequences for the evolution of the great apes?. Proceedings of the Royal Society B. 285 (1880): 20180859. Online here.
Caspar KR, Biggemann M, Geissmann T et al. 2021. Ocular pigmentation in humans, great apes, and gibbons is not suggestive of communicative functions. Sci Rep 11, 12994 (2021). https://doi.org/10.1038/s41598-021-92348-z

wiki/Gibbon

More gibbon traits: Decide if these seem human-like.

Homo longi, aka ‘dragon man’, compared to Hylobates, the gibbon

Source: https://pterosaurheresies.wordpress.com/2024/09/09/skin-eye-and-hair-color-in-humans-as-gibbon-descendants/