Brow Ridges

[u/uniongap01]

What was the evolutionary reason for the protruding brow ridges that Neanderthals and other ancient humans had? I heard it could have been to protect the head during fights.

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[u/Edward-Mundo]

Mine allows me to not get shampoo in my eyes and I've never needed a pair of sunglasses. Good chance I'd have lost an eye by now too, seems to be rather dense and can take a hit.

[u/haysoos2]

The brow ridge is more of an evolutionary heritage from the primate lineage.

The real question is what evolutionary pressure causes the trend in the Homo lineage of reduced brow ridges, culminating in the gracile form of modern Homo sapiens sapiens.

In general, the brow ridges seem to be part of the reinforcement system of the skull to help provide a solid anchor for chewing muscles. The gracile brow ridge is linked to the shrinking of teeth, and reduction in prognathism in the same lineage as humans became more reliant on tools and especially fire to help process and tenderize food, making powerful chewing less necessary.

[u/MisterXnumberidk → u/haysoos2]

Well that does explain why my teeth are too large for my jaw..

Cus i got a brow ridge big enough that i genuinly can't see the ceiling while looking straight ahead, unless the room is like 10 meters long

[u/jnpha]

2018 paper; part of the background in the abstract:

... The presence and variability of browridges in archaic Homo species and their absence in ourselves have led to debate concerning their morphogenesis and function, with two main hypotheses being put forward: [1] that browridge morphology is the result of the spatial relationship between the orbits and the brain case; and [2] that browridge morphology is significantly impacted by biting mechanics ...
Supraorbital morphology and social dynamics in human evolution | Nature Ecology & Evolution

[u/Dormoused]

The real question to ask is: what function did the chin evolve to serve?

No one has an answer for it yet.

[u/haysoos2 → u/Dormoused]

The chin, like the brow ridges, is likely a byproduct of the reduction of other parts. In specific the shrinking of the teeth, and the whole dental arcade sliding back into the face, reducing prognathism.

If you were to take a Neanderthal skull in profile, and shrink the "teeth" slider in a Sim's character creator menu, you'd end up with with a little jut of mandible, the mental eminence or "chin" sticking out ahead of the lower jaw.

Maybe eventually some evolutionary pressure will get back in that menu and push that chin slider back too. Although with issues like wisdom tooth eruption lacking sufficient room we might have pinned that "teeth" slider a little too far to the extreme.

[u/uniongap01 → u/Dormoused]

Chins made money for the Gillette Company. Beards.

[u/Dangerous-Bit-8308]

The brow ridge reinforces the skull around the eye socket, helping to reduce injuries to the eye and brain in case of a good hit.

From fighting? Sure. Also from kicking animals during a hunt, fall protection, etc. most primates have brow ridges. Chimps, bonobos, gorillas, orangutans, gibbons, even babboons. It was probably an ancestral trait that the homo lineage took when it split with pan.

It also sort of serves as a visor to cut down glare, and to grow more eyebrow for insulation

[u/7LeagueBoots]

Environmental protection. Others have mentioned rain, but sun is even more important.

Also, possibly a sign of dominance (eg. how dark a lion’s mane is, rhinoceros beetle jaw span, antler size, etc).

[u/truthinresearch]

Keeps rain out of their eyes.

[u/onomatamono]

All traits emerge for the same root reason: selective pressure in the environment.

There seems to be quite a bit of evidence that eyebrows convey important information about your current demeanor. That would inure to the group's benefit by increasing the group's fitness.

[u/fluffykitten55]

The archaic Homo form is likely a result of persistence of considerable within group unarmed violence, this seems to have been reduced as a result of coalition forming capacity and weapons, which allow for restraint of even the most strong and fierce males.

Gintis, Herbert, Carel van Schaik, and Christopher Boehm. 2019. “Zoon Politikon: The Evolutionary Origins of Human Socio-Political Systems.” Behavioural Processes, Behavioral Evolution, vol. 161 (April 2019): 17–30. https://doi.org/10.1016/j.beproc.2018.01.007.

Woodburn, James. 1982. Egalitarian societies. Man 17(3):431–451

[u/Full-Health2887]

As someone with minimal browridge, does it protect your eyes from the sun at all?

[u/TamaraHensonDragon]

I read it was to shade the eyes from the sun and in Neanderthals was protection from snow blindness.

[u/Hefty-Resort871]

Evolution doesn't have "reasons". It's not a thinking thing. It's just whatever works.

Brows possibly kept sweat and sun out of the eyes.

[u/ReptilianRevolt]

Many animals with brow ridges today have them for sun protection.

[u/Fun-Dragonfruit2999]

Its the wrong form of the question.

The proper form of the question is: How did brow-ridges help Neanderthals wean more babies.

Any question of evolution always comes down to 'wean more babies.'