9 ms·

How do they reconcile the fact that apparently only brains after 35k years ago show this new brain morphology when humans left Africa at least 70k years ago (wh

How do they reconcile the fact that apparently only brains after 35k years ago show this new brain morphology when humans left Africa at least 70k years ago (when they showed up in Australia). So one of the groups, either the "in Africa group" or the "out of Africa" group still should have the "old style brains" unless magically the changed happened in both groups at simultaneously. And yet I believe all humans currently alive have essentially similar brains.

astebbin 9y ago
It's uncomfortable to consider, but there is strong evidence to suggest that the brains of Australian aboriginal people differ in significant ways from their Caucasian bretheren. One study found the aboriginal visual cortex to be significantly larger than the Caucasian equivalent [0], possibly as an adaption to Australia's (visually) vast open spaces. The same study found the Caucasians had significantly larger parietal lobes and cerebellums - the same structures mentioned in this article. Another study found that Caucasians have significantly larger brains on average compared to those of aboriginals [1]. There's also evidence to suggest that modern humans from India [2] have contributed to the Australian gene pool for millennia (long before the arrival of the British), so more dramatic cranial differences may have already been averaged out. EDIT: deleted figure mis-remembered from an unrelated study. [0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1261675/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1261675/ [1] https://www.ncbi.nlm.nih.gov/pubmed/6926391 https://www.ncbi.nlm.nih.gov/pubmed/6926391 [2] http://www.pnas.org/content/110/5/1803 http://www.pnas.org/content/110/5/1803
- lobf 9y ago
  Isn't gene expression dependent on environment though? Is there some reason to believe that these differences are inherent, and not the result of gene expression being affected by the environment?
  - astebbin 9y ago
    IANA biologist. That said, if by "inherent" you mean primarily genetically determined, I'd say that explanation seems most likely given the evidence.
    - lobf 9y ago
      >primarily genetically determined Even this statement isn't as absolute as you seem to think it is. Your genes may or may not express based on the environment in which you grow up. Primarily genetically determined doesn't make sense, since genes aren't working in a vacuum.
  - TheAdamAndChe 9y ago
    > Is there some reason to believe that these differences are inherent, and not the result of gene expression being affected by the environment? That is a question that remains to be answered, and is only just beginning to be looked into through research on epigenetics[1]. [1] https://en.wikipedia.org/wiki/Epigenetics https://en.wikipedia.org/wiki/Epigenetics
    - why42 9y ago
      If our brain structures were different (at least in so far as the organization or distribution of cells within the cranium and not the external measurement) then one would expect adopted children from places where brains are very different to perform differently then peers in new locations. Yet I remember reading a study that showed that black children from Africa adopted by white parents in Germany performed at the same level as their peers. There have been other such studies with very similar conclusions.
      - ankjl 9y ago
        It could also be that differences in academic performance (I'm assuming academic is the performance you were referring to in your comment) are not accurate metrics for identifying the effects of differential brain organization. In scenarios like that, it's also difficult to control for the impact of different level of support for students in academic matters. For example, focused support for under-performing students compared to relatively relaxed support for students meeting expectations. I could probably also see the impact of different psychological factors associated with being adopted by a family on a different continent being hard to control for.
        why42 9y ago
        My rambling brain confounded a few studies I had read. My mistake. I was incorrect about the study being related to adoptions. It was actually something interesting that happened in Germany. I had read an environmental interpretation of the Eyferth Study: https://en.wikipedia.org/wiki/Eyferth_study https://en.wikipedia.org/wiki/Eyferth_study
- kakarot 9y ago
  We better get this racism thing in check before we're literally dealing with different species of human (assuming that some groups of people remain isolated and we don't experience total global homogeneity in the future)
  - taneq 9y ago
    What do you mean by "get in check"? It's pretty well accepted that we deal differently with different species. We'll need to decide what counts as ethically acceptable, but blind insistence that "all humans are created equal" isn't going to fly when we have undeniably different species of human.
    - kakarot 9y ago
      I mean racism needs to be obliterated before the differences our governments and world religions trick us into bickering about become even greater, and we regress on fair and ethical treatment of all people in both the eyes of the law and the heart of the common man.
  - tomrod 9y ago
    I thought racism was defined as: > prejudice, discrimination, or antagonism directed against someone of a different race based on the belief that one's own race is superior. I completely agree that when looking at differences among population groups in a species, one should avoid normative statements such as "such and such makes this population superior," but is there harm caused by identifying differences in averages, medians, and variance in said defined population groups? In other words, if I am speaking about dogs, is it inappropriate to say chihuahuas are on average smaller than boxers and labs? Same species, but distinct populations. I think that is at the heart of it. To be "colorblind" to both the historical and modern claims of specific population superiority in one dimension or another is misguided-bad claims made in good faith should be addressed head on, in requests for citations, evidence, etc. Similarly, to identify where differences may occur seems to be a reasonable action so long as there is recognition to cultural or historical drivers too, as GP implicitly identifies with the optical adaptation mentioned (though, TBH, I have not read the study he or she proffers and thus have no insight to the claim).
- kingkawn 9y ago
  Sounds much more like science revealing its still-lingering capacity for producing racist hierarchical judgements of human anatomy
  - astebbin 9y ago
    I honestly can't tell if this comment is satire. If it's not, please point to the racism. The study makes no moral judgement as to whether it's better to have a bigger parietal lobe vs. visual cortex. Do you think the study's results are somehow inaccurate, or improperly obtained?
- x2398dh1 9y ago
  From the article: > Only fossils younger than 35,000 years show the same globular shape as present-day humans and > They used state-of-art statistics to analyze endocasts of various fossils and present-day humans. There's nothing uncomfortable about this. They analyzed modern day humans and compared it to humans 35k years ago and found a statistical difference. "Uncomfortable" thoughts fall into the category of pseudoscience which has been long discredited - phrenology, essentially.
- anentropic 9y ago
  Is this any different to the "taxi drivers have bigger [part of] brains" or "musicians have bigger [part of] brains" memes that go around? i.e. true but insignificant
Arnt 9y ago
"Only fossils younger than 35,000 years show the same globular shape as present-day humans, suggesting that modern brain organization evolved some time between 100,000 and 35,000 years ago." If humans reached Australia well before 35,000 years ago and lived in isolation there and the evolutionary pressure in Australia differed noticeably from that in the rest of the world, then that narrows the gap. And, and.
- undersuit 9y ago
  I don't know how much isolation they had. The Sahul Schelf was walkable ground only 18,000 years ago by our current knowledge.
danieltillett 9y ago
There is the interesting hypothesis that the first people to reach Australia were the Denosovans and African peoples came much later. It would explain a lot of interesting observations about the peopling of Australia, not least evidence of there being people in Australia before African peoples had left the Middle East and why you can only find significant Denosovan genetic ancestory on the Australasian side of the Wallace line.
- ZeroGravitas 9y ago
  Your use of "African" seems confusing here. In particular the line "evidence of there being people in Australia before African peoples had left the Middle East" seems to suggest you think Denosovan people didn't originate in Africa.
  - danieltillett 9y ago
    Well the Denosovans really originated in East Asia somewhere as their ancestors left Africa a long time ago. We don't really have a good name for the ancient sub-Saharan humans that have contributed most of the genetic background to all living humans. The problem with the peopling of Australia is the time has been push back so far now (80K BCE) that it is before the ancient sub-Saharans really got much further than the Middle East.
  - dalbasal 9y ago
    We (sapiens) and perhaps late model erectus are the African species/subspecies of the archaic human group. Denisovans are Asian and neanderthals are European. It's all based on migration theories which are far from certain, currently. The story gets more complex with every find. The morrocan find is a spanner, as it "proves" a wide distribution of sapiens early on. This essentially excludes the idea of a migration out of the horn of Africa 200kya, the original out of Africa theory. Modern variations have gotten bigger. In the Levant neanderthals follow sapiens in the archeological record. The early sapiens are a little more neanderthal looking, especially the brows. This has lead some to a theory that neanderthals evolved from sapiens, and arboreal subspecies. The Australian story is even more confusing. 70kya is before behavioural modernity. But, seagoing boats are unmistakably modern behaviour. If modernity is strongly genetic, did (almost identical evidence) modernity evolve separately in Oz?... A lot of mystery still. We have very few finds.
chimprich 9y ago
> So one of the groups, either the "in Africa group" or the "out of Africa" group still should have the "old style brains" unless magically the changed happened in both groups at simultaneously. Just because one group migrated earlier doesn't mean they were genetically isolated. Presumably there were subsequent migrations, counter-migrations (of large populations and smaller groups) and associated interbreeding between them.
lawlessone 9y ago
That doesn't mean they were completely isolated once they arrived or that evolution stopped once they arrived.
Symmetry 9y ago
I'd tend to assume that any genetic trait that improves intelligence without significant drawbacks would spread rapidly through interbreeding and selective pressure even without wholesale population transfers. It took about 10,000 years for adult lactose tolerance to spread to its modern range and this brain organization trait would have 35,000 years and potentially give a larger selective benefit. EDIT: The corollary is that the large genetic component of intelligence is mostly non-linear. E.g. being heterozygous is an advantage and being homozygous a disadvantage.
- joshmarlow 9y ago
  > I'd tend to assume that any genetic trait that improves intelligence without significant drawbacks would spread rapidly through interbreeding... I would agree if we were confident that greater intelligence was always worth it, no matter the metabolic cost. Brains are expensive! Making them bigger incurs additional metabolic costs (and potential complications in the developmental phase). It's very possible that another 20 IQ points wouldn't have really made humans better hunter-gatherers, but would've meant they had to eat more. Granted, there are likely other ways to get smarter, but it's possible that there would be other systematic tradeoffs required.
  - Symmetry 9y ago
    Brain size is certainly an issue but from my understanding it's more about the constraints of childbirth than metabolic cost that are restraining it. When you're resting flat on your back your brain uses up 10 of the 100 watts you're dissipating but the variation in brain size given other constraints is pretty low and I'd expect plausible power differences from that to be pretty small too. And brain size only has something like a .3 correlation with IQ so other factors like efficient myelination or organization are probably much more important. I'd expect better myelination to reduce energy consumption if anything. As to organization I'm too unfamiliar with the scaling laws of neurons to be sure but I'd suspect brain organization that increased intelligence at least wouldn't increase energy usage much. So I'm still inclined to view intelligence as being constrained, evolutionarily, by issues of complexity rather than tradeoffs between efficiency and effectiveness as with height.

astebbin 9y ago

It's uncomfortable to consider, but there is strong evidence to suggest that the brains of Australian aboriginal people differ in significant ways from their Caucasian bretheren. One study found the aboriginal visual cortex to be significantly larger than the Caucasian equivalent [0], possibly as an adaption to Australia's (visually) vast open spaces. The same study found the Caucasians had significantly larger parietal lobes and cerebellums - the same structures mentioned in this article. Another study found that Caucasians have significantly larger brains on average compared to those of aboriginals [1]. There's also evidence to suggest that modern humans from India [2] have contributed to the Australian gene pool for millennia (long before the arrival of the British), so more dramatic cranial differences may have already been averaged out. EDIT: deleted figure mis-remembered from an unrelated study. [0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1261675/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1261675/ [1] https://www.ncbi.nlm.nih.gov/pubmed/6926391 https://www.ncbi.nlm.nih.gov/pubmed/6926391 [2] http://www.pnas.org/content/110/5/1803 http://www.pnas.org/content/110/5/1803

lobf 9y ago
Isn't gene expression dependent on environment though? Is there some reason to believe that these differences are inherent, and not the result of gene expression being affected by the environment?
- astebbin 9y ago
  IANA biologist. That said, if by "inherent" you mean primarily genetically determined, I'd say that explanation seems most likely given the evidence.
  - lobf 9y ago
    >primarily genetically determined Even this statement isn't as absolute as you seem to think it is. Your genes may or may not express based on the environment in which you grow up. Primarily genetically determined doesn't make sense, since genes aren't working in a vacuum.
- TheAdamAndChe 9y ago
  > Is there some reason to believe that these differences are inherent, and not the result of gene expression being affected by the environment? That is a question that remains to be answered, and is only just beginning to be looked into through research on epigenetics[1]. [1] https://en.wikipedia.org/wiki/Epigenetics https://en.wikipedia.org/wiki/Epigenetics
  - why42 9y ago
    If our brain structures were different (at least in so far as the organization or distribution of cells within the cranium and not the external measurement) then one would expect adopted children from places where brains are very different to perform differently then peers in new locations. Yet I remember reading a study that showed that black children from Africa adopted by white parents in Germany performed at the same level as their peers. There have been other such studies with very similar conclusions.
    - ankjl 9y ago
      It could also be that differences in academic performance (I'm assuming academic is the performance you were referring to in your comment) are not accurate metrics for identifying the effects of differential brain organization. In scenarios like that, it's also difficult to control for the impact of different level of support for students in academic matters. For example, focused support for under-performing students compared to relatively relaxed support for students meeting expectations. I could probably also see the impact of different psychological factors associated with being adopted by a family on a different continent being hard to control for.
      - why42 9y ago
        My rambling brain confounded a few studies I had read. My mistake. I was incorrect about the study being related to adoptions. It was actually something interesting that happened in Germany. I had read an environmental interpretation of the Eyferth Study: https://en.wikipedia.org/wiki/Eyferth_study https://en.wikipedia.org/wiki/Eyferth_study
kakarot 9y ago
We better get this racism thing in check before we're literally dealing with different species of human (assuming that some groups of people remain isolated and we don't experience total global homogeneity in the future)
- taneq 9y ago
  What do you mean by "get in check"? It's pretty well accepted that we deal differently with different species. We'll need to decide what counts as ethically acceptable, but blind insistence that "all humans are created equal" isn't going to fly when we have undeniably different species of human.
  - kakarot 9y ago
    I mean racism needs to be obliterated before the differences our governments and world religions trick us into bickering about become even greater, and we regress on fair and ethical treatment of all people in both the eyes of the law and the heart of the common man.
- tomrod 9y ago
  I thought racism was defined as: > prejudice, discrimination, or antagonism directed against someone of a different race based on the belief that one's own race is superior. I completely agree that when looking at differences among population groups in a species, one should avoid normative statements such as "such and such makes this population superior," but is there harm caused by identifying differences in averages, medians, and variance in said defined population groups? In other words, if I am speaking about dogs, is it inappropriate to say chihuahuas are on average smaller than boxers and labs? Same species, but distinct populations. I think that is at the heart of it. To be "colorblind" to both the historical and modern claims of specific population superiority in one dimension or another is misguided-bad claims made in good faith should be addressed head on, in requests for citations, evidence, etc. Similarly, to identify where differences may occur seems to be a reasonable action so long as there is recognition to cultural or historical drivers too, as GP implicitly identifies with the optical adaptation mentioned (though, TBH, I have not read the study he or she proffers and thus have no insight to the claim).
kingkawn 9y ago
Sounds much more like science revealing its still-lingering capacity for producing racist hierarchical judgements of human anatomy
- astebbin 9y ago
  I honestly can't tell if this comment is satire. If it's not, please point to the racism. The study makes no moral judgement as to whether it's better to have a bigger parietal lobe vs. visual cortex. Do you think the study's results are somehow inaccurate, or improperly obtained?
x2398dh1 9y ago
From the article: > Only fossils younger than 35,000 years show the same globular shape as present-day humans and > They used state-of-art statistics to analyze endocasts of various fossils and present-day humans. There's nothing uncomfortable about this. They analyzed modern day humans and compared it to humans 35k years ago and found a statistical difference. "Uncomfortable" thoughts fall into the category of pseudoscience which has been long discredited - phrenology, essentially.
anentropic 9y ago
Is this any different to the "taxi drivers have bigger [part of] brains" or "musicians have bigger [part of] brains" memes that go around? i.e. true but insignificant

Arnt 9y ago

"Only fossils younger than 35,000 years show the same globular shape as present-day humans, suggesting that modern brain organization evolved some time between 100,000 and 35,000 years ago." If humans reached Australia well before 35,000 years ago and lived in isolation there and the evolutionary pressure in Australia differed noticeably from that in the rest of the world, then that narrows the gap. And, and.

undersuit 9y ago
I don't know how much isolation they had. The Sahul Schelf was walkable ground only 18,000 years ago by our current knowledge.

danieltillett 9y ago

There is the interesting hypothesis that the first people to reach Australia were the Denosovans and African peoples came much later. It would explain a lot of interesting observations about the peopling of Australia, not least evidence of there being people in Australia before African peoples had left the Middle East and why you can only find significant Denosovan genetic ancestory on the Australasian side of the Wallace line.

ZeroGravitas 9y ago
Your use of "African" seems confusing here. In particular the line "evidence of there being people in Australia before African peoples had left the Middle East" seems to suggest you think Denosovan people didn't originate in Africa.
- danieltillett 9y ago
  Well the Denosovans really originated in East Asia somewhere as their ancestors left Africa a long time ago. We don't really have a good name for the ancient sub-Saharan humans that have contributed most of the genetic background to all living humans. The problem with the peopling of Australia is the time has been push back so far now (80K BCE) that it is before the ancient sub-Saharans really got much further than the Middle East.
- dalbasal 9y ago
  We (sapiens) and perhaps late model erectus are the African species/subspecies of the archaic human group. Denisovans are Asian and neanderthals are European. It's all based on migration theories which are far from certain, currently. The story gets more complex with every find. The morrocan find is a spanner, as it "proves" a wide distribution of sapiens early on. This essentially excludes the idea of a migration out of the horn of Africa 200kya, the original out of Africa theory. Modern variations have gotten bigger. In the Levant neanderthals follow sapiens in the archeological record. The early sapiens are a little more neanderthal looking, especially the brows. This has lead some to a theory that neanderthals evolved from sapiens, and arboreal subspecies. The Australian story is even more confusing. 70kya is before behavioural modernity. But, seagoing boats are unmistakably modern behaviour. If modernity is strongly genetic, did (almost identical evidence) modernity evolve separately in Oz?... A lot of mystery still. We have very few finds.

chimprich 9y ago

> So one of the groups, either the "in Africa group" or the "out of Africa" group still should have the "old style brains" unless magically the changed happened in both groups at simultaneously. Just because one group migrated earlier doesn't mean they were genetically isolated. Presumably there were subsequent migrations, counter-migrations (of large populations and smaller groups) and associated interbreeding between them.

lawlessone 9y ago

That doesn't mean they were completely isolated once they arrived or that evolution stopped once they arrived.

Symmetry 9y ago

I'd tend to assume that any genetic trait that improves intelligence without significant drawbacks would spread rapidly through interbreeding and selective pressure even without wholesale population transfers. It took about 10,000 years for adult lactose tolerance to spread to its modern range and this brain organization trait would have 35,000 years and potentially give a larger selective benefit. EDIT: The corollary is that the large genetic component of intelligence is mostly non-linear. E.g. being heterozygous is an advantage and being homozygous a disadvantage.

joshmarlow 9y ago
> I'd tend to assume that any genetic trait that improves intelligence without significant drawbacks would spread rapidly through interbreeding... I would agree if we were confident that greater intelligence was always worth it, no matter the metabolic cost. Brains are expensive! Making them bigger incurs additional metabolic costs (and potential complications in the developmental phase). It's very possible that another 20 IQ points wouldn't have really made humans better hunter-gatherers, but would've meant they had to eat more. Granted, there are likely other ways to get smarter, but it's possible that there would be other systematic tradeoffs required.
- Symmetry 9y ago
  Brain size is certainly an issue but from my understanding it's more about the constraints of childbirth than metabolic cost that are restraining it. When you're resting flat on your back your brain uses up 10 of the 100 watts you're dissipating but the variation in brain size given other constraints is pretty low and I'd expect plausible power differences from that to be pretty small too. And brain size only has something like a .3 correlation with IQ so other factors like efficient myelination or organization are probably much more important. I'd expect better myelination to reduce energy consumption if anything. As to organization I'm too unfamiliar with the scaling laws of neurons to be sure but I'd suspect brain organization that increased intelligence at least wouldn't increase energy usage much. So I'm still inclined to view intelligence as being constrained, evolutionarily, by issues of complexity rather than tradeoffs between efficiency and effectiveness as with height.