[This post is under construction, beware of detouring thoughts, meandering meanings...]
DM: Hearing in water is not the same as sonar, just like hearing in air is not the same as sonar -- bats have sonar, we don't.
DD: False. Sonar uses echoes of sound energy waves (in water or air) to determine relative position in the same way that vision does using light energy. As in a blind person with cane or oral clicking. Google.
The tiny inner ear cells in humans are hair cells (cilia per DM), derived from the anterior sensory hair cells of the lateral line in fish. Yes, it has something to do with water, sound energy frequencies (vibrations) provide information about the environment, likely these hairs had once been external vibrissae for the crustacean-fish last common ancestor.
However, I was speaking of the middle ears, the little bones and eustachian tubes to the nasal cavity. A human non-scuba diver can submerge and allow seawater into the nasal cavity and middle ears (in order to avoid gas-equalization problems at depth), while the soft palate separates the nasal cavity from the oral cavity.
Notably sound is then magnified (increased sound conduction via bones and dissonance is reduced) at depth, as compared to having air filled middle ears, since there is electrolytic liquid in the inner ears, middle ears, and external ears. Thus humans retain a weak form of sonar capability, though far inferior to that of the specialized fish chasing dolphins.
DD: Dive-Song is simply the brief description of the causative agent for many "special" traits of humans. White eyes (enlarged sclerae), monogamy, reduced size dimorphism compared to apes, singing, humming, clicking, music, epicanthal eyelids, primitive pinnae, unusual breathing adaptations, photic sneezing, eating raw shellfish, gift-giving-trade, sustained vocal communication, facial gestures, much reduced laryngeal air sacs compared to similar sized apes, etc. etc.
Speculative zoology? Yes, but strongly correlative biology and ecology and anthropology (when not dismissed by savanna-centered theorists). Does Dive-Song answer all the questions? No just a few of the hardest.
Savanna woodlands were occupied by humans much much later, after development of dug-out boats and tools allowed safe passage inland, previous to that trees and cliffs provided the only refuge from large predators, producing the arboreal apes. Tropical rainforests inland were obviously not where humans diverged from other apes. Anything which places ancient human ancestors 7-1ma long distances away from the shores (previous to boats) adds complexity (abundant sweating = needs abundant salt + water, freshwater not enough).
DM: I did [look at the Dive Song brief]. I conclude that you got the idea that human hearing has something to do with water, so you made up an elaborate scenario to explain that.
DD: Nope. I just connected the facts in the most parsimonious manner. And that my friend is Science.
DM: "Don't you read anything about chemistry, .."
DM: "Most atomic nuclei are not spheres; they occupy a wide range from cigar-shaped to disk-shaped."
DM: "it was in a Scientific American special volume that I read long ago."
DD: 1) Yes. 2) False. 3) False. One must study and understand the primacy of the spherical shape in nature before one can speak intelligibly about egg shapes, planets, nuclear fission-fusion, meiosis-mitosis, gravity-density, diffusion-radiation, conduction-convection, erosion-deposition, estrus-menstrual cycles, etc. Else it is just blowing hot air. I just connected the facts in the most parsimonious manner.
DM: It's not the most parsimonious possibility -- the whole diving stuff is not needed to explain the features you mentioned. It is an unnecessary ad hoc assumption. One must study and understand the primacy of the spherical shape in nature before one can speak intelligibly about [...]
DM: First, one must find out whether there is, in a meaningful way, such a thing as "the primacy of the spherical shape in nature". You assume a priori that there's a common underlying reason for all spheres, even if this necessitates introducing an ad hoc assumption. What if one sphere has nothing to do with another?
DD: Odd statement, sphere's share common sphericity, that is not nothing.
DM: And no, spheres have zero to do with meiosis, mitosis, gravity, density, or menstruation. If you have evidence to the contrary, please tell me.
DD: "spherical shape of most nuclei" as I referenced earlier, do you dispute that? Even simple nuclei tend toward sphericity, although they don't resemble perfect spheres due to having only a small quantity of neutrons and protons. Eg. a nucleus of 2 P and 2 N might appear tetrahedral, but are the most spherically possible shape when Nucleons = 4.
To avoid repeating, here's an online text helpful in comprehending the properties of common sphericity in nature, by the inventor of the geodesic dome.
http://www.rwgrayprojects.com/synergetics/synergetics.html
The tiny inner ear cells in humans are hairs (hair cells), derived from the anterior sensory hairs of the lateral line in fish. Yes, it has something to do with water, sound energy frequencies (vibrations) provide information about the environment, likely these hairs had once been external vibrissae for the crustacean-fish last common ancestor.
However, I was speaking of the middle ears, the little bones and eustachian tubes to the nasal cavity. A human non-scuba diver can submerge and allow seawater into the nasal cavity and middle ears (in order to avoid gas-equalization problems at depth), while the soft palate separates the nasal cavity from the oral cavity.
Notably sound is then magnified (increased sound conduction via bones and dissonance is reduced) at depth, as compared to having air filled middle ears, since there is electrolytic liquid in the inner ears, middle ears, and external ears. Thus humans retain a weak form of sonar capability, though far inferior to that of the specialized fish chasing dolphins.
Dive-Song is simply the brief description of the causative agent for many "special" traits of humans. White eyes (enlarged sclerae), monogamy, reduced size dimorphism compared to apes, singing, humming, clicking, music, epicanthal eyelids, primitive pinnae, unusual breathing adaptations, photic sneezing, eating raw shellfish, gift-giving-trade, sustained vocal communication, facial gestures, much reduced laryngeal air sacs compared to similar sized apes, etc. etc.
Speculative zoology? Yes, but strongly correlative biology and ecology and anthropology (when not dismissed by savanna-centered theorists). Does Dive-Song answer all the questions? No just a few of the hardest.
Savanna woodlands were occupied by humans much much later, after development of dug-out boats and tools allowed safe passage inland, previous to that trees and cliffs provided the only refuge from large predators, producing the arboreal apes. Tropical rainforests inland were obviously not where humans diverged from other apes.
DDeden
DD: I used those as modern examples (reindeer, grey whales, figs) as parallels with past events of evolutionary significance, since I'm not familiar with specific pre-pleistocene mammals and plants.
MD: Here we have the problem. Why do you talk about things that you know full well you don't understand? Learn about them first, and then come back -- before then you won't know which parts of today's biosphere are parallels to past conditions and which are not.
DD: Point taken, I doubt I have much time to dig so deeply and thoroughly. However, life today does not differ very much from life 20 or 200 million years ago, if one understands natural selection, which I do, and one has good data on climate-environmental changes which I don't.
DDeden
(My "I see" comment refers to my underappreciation of the diversity of snake tooth shapes.)
Please substantiate your claim that "ppt" means "part per trillion".
Don't you read anything about chemistry, including reports of pollution? Google for "parts per trillion", and you'll see... percent, permil, ppm, ppb, ppt, ppq. I have seen "ppt" used for "parts per thousand", but that's a rare mistake.
DD: I've found nothing to substantiate your claim. Please provide a ref.
Sorry, it was in a Scientific American special volume that I read long ago. But what results did you get from googling for "double magic" nucleus? Does none of them help?
The tiny inner ear cells in humans are hairs, derived from the anterior sensory hairs of the lateral line in fish.
They are not hairs, they are cilia (and thus outgrowths of cells, not that it matters here). Cilia occur in lots of sense organs, like vertebrate eyes and the lateral line organ, so you're right that the inner ear and the lateral line organ are on some level the same, "fish" have their own inner ears. We're talking about vertebrate inner ears, not human inner ears which are in no way special.
likely these hairs had once been external vibrissae for the crustacean-fish last common ancestor.
No, that common ancestor had cilia all over its skin and used them for locomotion (in addition to having specialized cilia in certain sense organs, e.g. one kind of eye). Flatworms, nemertines and several other clades still move that way most of the time (like Paramecium).
Notably sound is then magnified (increased sound conduction via bones and dissonance is reduced) at depth, as compared to having air filled middle ears, since there is electrolytic liquid in the inner ears, middle ears, and external ears.
Fine.
Thus humans retain a weak form of sonar capability
Hearing in water is not the same as sonar, just like hearing in air is not the same as sonar -- bats have sonar, we don't.
The soft palate is common to all mammals.
Dive-Song is simply the brief description of the causative agent for many "special" traits of humans. White eyes (enlarged sclerae), monogamy, reduced size dimorphism compared to apes, singing, humming, clicking, music, epicanthal eyelids, primitive pinnae, unusual breathing adaptations, photic sneezing, eating raw shellfish, gift-giving-trade, sustained vocal communication, facial gestures, much reduced laryngeal air sacs compared to similar sized apes, etc. etc.
Fine, but it's still a just-so story. It doesn't explain anything that can't be explained otherwise. (Except maybe for the sclerae -- can you direct me to more info about those? What are epicanthal eyelids, and what do you mean by pinnae -- certainly not the external ears?) Let me try:
- We are, on average, not monogamous. We fuck around almost like bonobos.
- Reduced size dimorphism comes with reduced male-male competition, as do the shrunken canines and the absence of large laryngeal air sacs. Make love, not war... see above.
- Music including singing and humming can be explained in lots of other ways that don't necessitate regular diving. Try communication. Anything can come out of a brain as bloated as ours.
- Clicking? Do you mean click consonants?
-- These have probably developed from consonant clusters. Plenty of languages in West Africa today have coarticulated kp and/or gb, that is, you put the tongue against the velum, close the lips, and then open both closures at almost the same time. Try pronouncing that. More often than not you'll open the lips just before instead of just after the velar closure. Voilà, the bilabial click. link
-- The idea that the last common ancestor of all extant languages contained click consonants comes from the idea that the Khoisan languages are the sister-group to all the rest. Even if that is true, and even if the presence of clicks in all Khoisan languages is retained (plesiomorphic) instead of an innovation (autapomorphic), clicks can still have arisen in the MRCA of all extant languages as described above. Keep in mind that there's no evidence that the MRCA of all extant languages was the first language; most likely, it was spoken long after the first language.
- What do you mean by "unusual breathing adaptations", and how many of these have been tested in other mammals, especially other apes? It is indeed interesting that our heart rate drops when we dive -- but we don't know if the same happens to a chimp, because chimps don't dive. Maybe we could convince an orang-utan to do it; they do go quite deep into water if they need to.
- "Photic sneezing" means having to sneeze when looking into the sun, right? I don't have that, and I don't think it's widespread, so I don't think it's likely that any population of our ancestors all had it. On the other hand, how widespread is it beyond humans? Do any chimps have it?
- We are the only apes that ever get a chance to eat raw shellfish. You don't know if there's any "special trait of humans" involved here; as long as you don't, you can't hope to explain anything about it.
- Gifts are widespread among mammals and birds. Trade and communication come with a bloated brain -- and how other than vocal would you communicate? Constantly having to look at each other is a disadvantage. I'm trying to say "sustained vocal communication" doesn't need an explanation at all.
- Facial gestures are normal for Old World monkeys at the least. Nothing to explain here.
Savanna woodlands were occupied by humans much much later, after development of dug-out boats and tools allowed safe passage inland,
Then why do we find their remains long, long before any kind of boat?
previous to that trees and cliffs provided the only refuge from large predators, producing the arboreal apes.
Arboreality is the normal state for primates; it does not need to be explained. You are right that the loss of arboreality needs to be explained -- and that happened twice, because 5 % of all surviving chimps live in the savanna. Predators are not much of a concern for a group of chimps; they are famous for putting up a fight, with weapons.
Tropical rainforests inland were obviously not where humans diverged from other apes.
The oldest human remains do not come from outright rainforests, but still from wooded environments with a more or less closed canopy. The savanna came later, when the forest shrunk.
DM: I did [look at the Dive Song brief]. I conclude that you got the idea that human hearing has something to do with water, so you made up an elaborate scenario to explain that.
Nope. I just connected the facts in the most parsimonious manner. And that my friend is Science.
DDeden
> I forgot to mention: you can't eat the eggs of a mosasaur or
plesiosaur any more than those of a stagodontid or "pediomyid"
metatherian.
On the effect of the K/Pg extinction on stagodontids:
It might be wishful thinking on my side - I happen to like stagodontids - but doesn`t Eobrasilia look like a post-K/Pg (Itaboraian) survivor?
Marshal (Journal of Paleontology, Vol 58, No 1; Jan. 1984; pp. 173-177)
seems to come to the same conclusion.
DM: "Don't you read anything about chemistry, .."
DM: "Most atomic nuclei are not spheres; they occupy a wide range from cigar-shaped to disk-shaped."
DM: "it was in a Scientific American special volume that I read long ago."
DD: 1) Yes. 2) False. 3) False. One must study and understand the primacy of the spherical shape in nature before one can speak intelligibly about egg shapes, planets, nuclear fission-fusion, meiosis-mitosis, gravity-density, diffusion-radiation, conduction-convection, erosion-deposition, estrus-menstrual cycles, etc. Else it is just blowing hot air.
DDeden
Nope. I just connected the facts in the most parsimonious manner.
It's not the most parsimonious possibility -- the whole diving stuff is not needed to explain the features you mentioned. It is an unnecessary ad hoc assumption.
One must study and understand the primacy of the spherical shape in nature before one can speak intelligibly about [...]First, one must find out whether there is, in a meaningful way, such a thing as "the primacy of the spherical shape in nature". You assume a priori that there's a common underlying reason for all spheres, even if this necessitates introducing an ad hoc assumption. What if one sphere has nothing to do with another?
And no, spheres have zero to do with meiosis, mitosis, gravity, density, or menstruation. If you have evidence to the contrary, please tell me.
Congratulations! You're reaching the average thread length of Pharyngula! :-)
"spherical shape of most nuclei" as I referenced earlier, do you dispute that? Even simple nuclei tend toward sphericity, although they don't resemble perfect spheres due to having only a small quantity of neutrons and protons. Eg. a nucleus of 2 P and 2 N might appear tetrahedral, but are the most spherically possible shape when Nucleons = 4.
Anything which places ancient human ancestors 7-1ma long distances away from the shores (previous to boats) adds complexity (abundant sweating = needs abundant salt + water, freshwater not enough).
-----
85 comments (+1).
DDeden
We just had a computer crash, I think I sent a comment just now, but not sure if it posted. To avoid repeating, here's an online text helpful in comprehending the properties of common sphericity in nature, by the inventor of the geodesic dome.
http://www.rwgrayprojects.com/synergetics/synergetics.html
DDeden
DM: Hearing in water is not the same as sonar, just like hearing in air is not the same as sonar -- bats have sonar, we don't.
DD: False. Sonar uses echoes (water or air), aka blind person with cane or oral clicking. Google.
DD: Dive-Song is simply the brief description of ...
DM: Fine, but it's still a just-so story. It doesn't explain anything that can't be explained otherwise.
DD: It explains them most parsimoniously, these functions all worked together and were selected for.
DM: (Except maybe for the sclerae -- can you direct me to more info about those? What are epicanthal eyelids, and what do you mean by pinnae -- certainly not the external ears?) Let me try:
DD: Jane Goodall found 1 chimp with white sclerae, and the albino gorilla Snowflake had white sclerae, all other apes & monkeys (and nearly all mammals) do not have exposed/enlarged white sclerae. All humans do, although Central Africans have a yellowish tint. Why? It fits perfectly into a diving scenario for our ancestors. As well the epicanthic (slant) eyelids of the Khoisan, some Nubian and Middle Eastern and East Asian people, and the previous reduction and subsequent enlargement of the pinnae and poor ear muscular control compared to typical arboreal and savanna spp.
DM: We are, on average, not monogamous. We fuck around almost like bonobos.
DD: We (viewed as all age, not just young adult) are far more monogamous than any great ape.
DM: Reduced size dimorphism comes with reduced male-male competition, as do the shrunken canines and the absence of large laryngeal air sacs. Make love, not war... see above.
DD: Is this found in any typical savanna or arboreal spp.?
Savanna chimps tend to be more dimorphic (and less bipedal) than rainforest bonobos. Since you have stated human ancestors were on the savannas, how do you resolve this?
It would however be expected to occur if the male & female (with infant) dove together alternatively, changing from direct male-male competition to male/female-male/female, something which could not occur terrestrially but could occur at the shores and arboreally (see partial parallel in gibbons re. air sacs).
DM: Music including singing and humming can be explained in lots of other ways that don't necessitate regular diving. Try communication. Anything can come out of a brain as bloated as ours.
DD: What savanna/woodland mammals sing or hum? Notably, arboreal songbirds sing, ground birds don't. Presuming our ancestors were terrestrial, what indicates that they would sing and hum? Why would they alter from a loud long call to a continuous vocalizing pattern? Mice have proportionately larger brains than humans, and they sing and live on savannas, is that the only comparison?
DM: Clicking? Do you mean click consonants?
-- These have probably developed from consonant clusters.
DD: Clicks as you noted. Ancient, unknown date of origin, possibly derived from breath holding mannerisms.
DM: What do you mean by "unusual breathing adaptations", and how many of these have been tested in other mammals, especially other apes? It is indeed interesting that our heart rate drops when we dive -- but we don't know if the same happens to a chimp, because chimps don't dive. Maybe we could convince an orang-utan to do it; they do go quite deep into water if they need to.
DD: Although uncertain, I'd guess any great ape immersed would fill their laryngeal air sac with exhaled air and could not dive.
DM: "Photic sneezing" means having to sneeze when looking into the sun, right? I don't have that, and I don't think it's widespread, so I don't think it's likely that any population of our ancestors all had it. On the other hand, how widespread is it beyond humans? Do any chimps have it?
Darwin found no sun-frown and assumably no sun-sneeze when he tested a young chimp and orang from very dark to bright light conditions. Uniquely human AFAIK, but likely similar to marine iguanas which look at the sun and sneeze to remove salt brine from nasal glands (they dive and eat salty seaweed). The photic sneeze exhales old air from the body entirely at roughly the same speed as a dolphin ventilatory cycle, far faster than a normal aerobic exhale in a human.
DM: We are the only apes that ever get a chance to eat raw shellfish. You don't know if there's any "special trait of humans" involved here; as long as you don't, you can't hope to explain anything about it.
DD: Chimps eat freshwater shrimp larvae in inland non-tidal streams underneath leaves. No apes live on tidal waters, apes developed their derivations (eg. longer fingers) as they moved from the coasts inland.
DM: Gifts are widespread among mammals and birds. Trade and communication come with a bloated brain -- and how other than vocal would you communicate?
DD: Savanna animals typically use scent and visual, vocal is usually danger-related. Mammalian gift-giving not so common (exc. chimp male exchange food for sex with older females)
DM: Constantly having to look at each other is a disadvantage. I'm trying to say "sustained vocal communication" doesn't need an explanation at all.
DD: How many inland wooded savanna spp. have sustained vocal communication?
DD: Savanna woodlands were occupied by humans much much later, after development of dug-out boats and tools allowed safe passage inland,
DM: Then why do we find their remains long, long before any kind of boat?
DD: Butted hand axe/adze remnants (Eritrea reef 125,000yrs) indicate possible dug-out contsruction. Boats rot quickly, bones less so, teeth less so. There were certainly hominids inland with at least partial arboreal adaptations, but our ancestors were generally along coasts and near-shore isles.
No doubt however there was indeed some mixing, simply due to the long periods involved.
DD: previous to that trees and cliffs provided the only refuge from large predators, producing the arboreal apes.
DM: Arboreality is the normal state for primates; it does not need to be explained. You are right that the loss of arboreality needs to be explained -- and that happened twice, because 5 % of all surviving chimps live in the savanna. Predators are not much of a concern for a group of chimps; they are famous for putting up a fight, with weapons.
DD: Fight against a small leopard perhaps, no chance against a lion, dead meat. That's why savanna chimps stay near trees, and why our ancestors avoided that whole scene until they came upstream on boats.
DM: The oldest human remains do not come from outright rainforests, but still from wooded environments with a more or less closed canopy. The savanna came later, when the forest shrunk.
DD: The further away from seashores/isles, no matter what eco-type, the less likely a non-tree-sleeper would survive, until dug-outs (and fire?), due to the big cats. Human ancestors lost their tree gripping feet a long time ago, and consider the pregnant females & chubby infants, very unlike the lightning fast quadruped baboons and patas monkeys.
I considder it most likely that at different periods, our ancestors were islanded but sometimes able to travel to coastal shores, with variable results (like sea turtles and croc populations, unlike inland theropods or sauropods). They weren't absolutely island isolates.
Gosh, enough already!
DDeden
DM: Fine, but it's still a just-so story. It doesn't explain anything that can't be explained otherwise.
DD: It explains them most parsimoniously, these functions all worked together and were selected for.
DM: (Except maybe for the sclerae -- can you direct me to more info about those? What are epicanthal eyelids, and what do you mean by pinnae -- certainly not the external ears?) Let me try:
DD: Jane Goodall found 1 chimp with white sclerae, and the albino gorilla Snowflake had white sclerae, all other apes & monkeys (and nearly all mammals) do not have exposed/enlarged white sclerae. All humans do, although Central Africans have a yellowish tint. Why? It fits perfectly into a diving scenario for our ancestors. As well the epicanthic (slant) eyelids of the Khoisan, some Nubian and Middle Eastern and East Asian people, and the previous reduction and subsequent enlargement of the pinnae and poor ear muscular control compared to typical arboreal and savanna spp.
DM: We are, on average, not monogamous. ... like bonobos.
DD: We (viewed as all age, not just young adult) are far more monogamous than any great ape.
DM: Reduced size dimorphism comes with reduced male-male competition, as do the shrunken canines and the absence of large laryngeal air sacs. Make love, not war... see above.
DD: Is this found in any typical savanna or arboreal spp.?
Savanna chimps tend to be more dimorphic (and less bipedal) than rainforest bonobos. Since you have stated human ancestors were on the savannas, how do you resolve this?
DD: It would however be expected to occur if the male & female (with infant) dove together alternatively, changing from direct male-male competition to male/female-male/female, something which could not occur terrestrially but could occur at the shores and arboreally (see partial parallel in gibbons re. air sacs).
DM: Music including singing and humming can be explained in lots of other ways that don't necessitate regular diving. Try communication. Anything can come out of a brain as bloated as ours.
DD: What savanna/woodland mammals sing or hum? Notably, arboreal songbirds sing, ground birds don't. Presuming our ancestors were terrestrial, what indicates that they would sing and hum? Why would they alter from a loud long call to a continuous vocalizing pattern? Mice have proportionately larger brains than humans, and they sing and live on savannas, is that the only comparison?
DM: Clicking? Do you mean click consonants?
-- These have probably developed from consonant clusters.
DD: Clicks as you noted. Ancient, unknown date of origin, possibly derived from breath holding mannerisms.
DM: What do you mean by "unusual breathing adaptations", and how many of these have been tested in other mammals, especially other apes? It is indeed interesting that our heart rate drops when we dive -- but we don't know if the same happens to a chimp, because chimps don't dive. Maybe we could convince an orang-utan to do it; they do go quite deep into water if they need to.
DD: Although uncertain, I'd guess any great ape immersed would fill their laryngeal air sac with exhaled air and could not dive.
DM: "Photic sneezing" means having to sneeze when looking into the sun, right? I don't have that, and I don't think it's widespread, so I don't think it's likely that any population of our ancestors all had it. On the other hand, how widespread is it beyond humans? Do any chimps have it?
DD: Darwin found no sun-frown and assumably no sun-sneeze when he tested a young chimp and orang from very dark to bright light conditions. Uniquely human AFAIK, but likely similar to marine iguanas which look at the sun and sneeze to remove salt brine from nasal glands (they dive and eat salty seaweed). The photic sneeze exhales old air from the body entirely at roughly the same speed as a dolphin "spouting" ventilatory cycle, far faster than a normal aerobic exhale in a human.
DM: We are the only apes that ever get a chance to eat raw shellfish. You don't know if there's any "special trait of humans" involved here; as long as you don't, you can't hope to explain anything about it.
DD: Chimps eat freshwater shrimp larvae in inland non-tidal streams underneath leaves. No apes live on tidal waters, apes developed their derivations (eg. longer fingers) as they moved from the coasts inland.
DM: Gifts are widespread among mammals and birds. Trade and communication come with a bloated brain -- and how other than vocal would you communicate?
DD: Savanna animals typically use scent and visual, vocal is usually danger-related. Mammalian gift-giving not so common (exc. chimp male exchange food for sex with older females)
DM: Constantly having to look at each other is a disadvantage. I'm trying to say "sustained vocal communication" doesn't need an explanation at all.
DD: How many inland wooded savanna spp. have sustained vocal communication?
DD: Savanna woodlands were occupied by humans much much later, after development of dug-out boats and tools allowed safe passage inland,
DM: Then why do we find their remains long, long before any kind of boat?
DD: Butted hand axe/adze remnants (Eritrea reef 125,000yrs) indicate possible dug-out contsruction. Boats rot quickly, bones less so, teeth less so. There were certainly hominids inland with at least partial arboreal adaptations, but our ancestors were generally along coasts and near-shore isles.
No doubt however there was indeed some mixing, simply due to the long periods involved.
DD: previous to that trees and cliffs provided the only refuge from large predators, producing the arboreal apes.
DM: Arboreality is the normal state for primates; it does not need to be explained. You are right that the loss of arboreality needs to be explained -- and that happened twice, because 5 % of all surviving chimps live in the savanna. Predators are not much of a concern for a group of chimps; they are famous for putting up a fight, with weapons.
DD: Fight against a small leopard perhaps, no chance against a lion, dead meat. That's why savanna chimps stay near trees, and why our ancestors avoided that whole scene until they came upstream on boats.
DM: The oldest human remains do not come from outright rainforests, but still from wooded environments with a more or less closed canopy. The savanna came later, when the forest shrunk.
DD: The further away from seashores/isles, no matter what eco-type, the less likely a non-tree-sleeper would survive, until dug-outs (and fire?), due to the big cats. Human ancestors lost their tree gripping feet a long time ago, and consider the pregnant females & chubby infants, very unlike the lightning fast quadruped baboons and patas monkeys.
DD: I consider it most likely that at different periods, our ancestors were islanded but sometimes able to travel to coastal shores, with variable results (like sea turtles and croc populations, unlike inland theropods or sauropods). They weren't absolutely island isolates.
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