Chimpanzee 'mini-brains' hint at secrets of human evolution

Chimpanzee ‘mini-brains’ hint at secrets of human evolution
A chimpanzee (Pan troglodytes) mother nursing her baby in Tanzania’s Mahale Mountains National Park, on the shores of Lake Tanganyika, where study co-author Alex Pollen was first inspired to study human and chimpanzee brain evolution. Credit: Susan K. McConnell for Cell Press

At some point during human evolution, a handful of genetic changes triggered a dramatic threefold expansion of the brain's neocortex, the wrinkly outermost layer of brain tissue responsible for everything from language to self-awareness to abstract thought. Identifying what drove this evolutionary shift is fundamental to understanding what makes us human, but has been particularly challenging for scientists because of ethical prohibitions against studying the developing brains of our closest living relative, the chimpanzee, in the lab.

"By birth, the human cortex is already twice as large as in the chimpanzee, so we need to go back much earlier into to understand the events that drive this incredible growth," said Arnold Kriegstein, MD, Ph.D., the John Bowes Distinguished Professor in Stem Cell and Tissue Biology, founding director of the Eli and Edyth Broad Center of Regenerative Medicine and Stem Cell Research at UC San Francisco, and member of the UCSF Weill Institute for Neurosciences.

In a study published February 7, 2019, in Cell, Kriegstein and collaborators have gotten around this impasse by creating chimpanzee "organoids"—small clusters of brain cells grown from in a laboratory dish that mimic the development and organization of full-size brains.

Kriegstein's group was among the early pioneers of growing human brain organoids from so-called induced (iPSCs)—adult cells (usually skin cells) reprogrammed into stem cells that can become any tissue in the body. Organoids have since become a valuable tool for studying human tissue development and disease in a controlled laboratory setting, but the new study, in which the researchers generated 56 organoids from stem cells derived from the skin of eight and 10 humans, marks the first time researchers have been able to produce and study chimpanzee brain organoids en masse.

"Our ability to take skin cells from an adult chimpanzee, turn them into iPSCs, and then study their development in laboratory dishes is astounding," said Kriegstein. "It's a 'science fiction' experiment that couldn't have happened 10 years ago."

"These chimpanzee organoids give us an otherwise inaccessible window to six million years of our evolution. They let us ask new questions about what makes us human," added study co–first author Alex Pollen, Ph.D., an assistant professor of neurology and former Kriegstein lab postdoctoral researcher, who led the development of the new great ape stem cell and technology.

Chimpanzee ‘mini-brains’ hint at secrets of human evolution
The human (left) and chimpanzee (right) brain organoids contain multiple types of neural stem cells (red and green) and mature brain cells (magenta and cyan), mimicking the development of real human and chimpanzee brains. (Scale bar 100 micrometers). Credit: Pollen and Kriegstein Labs / UCSF

In the new study, co–first author Aparna Bhaduri, Ph.D., a postdoctoral researcher in the Kriegstein lab, deconstructed human and chimpanzee organoids at different stages of development, allowing her to directly compare the specific cell types and genetic programs that orchestrate the growth of the chimp and human brain.

By looking for differences in gene activity between human organoids and chimp organoids (as well as reference tissue from another primate, the rhesus macaque monkey) Bhaduri identified several hundred genetic changes unique to the human lineage that could help explain the evolutionary origins of the distinctly human brain.

For instance, Bhaduri discovered that neural precursor cells called outer radial (oRG)—originally discovered by the Kriegstein lab—showed heightened activity of a key growth signaling network known as the mTOR pathway in human organoids.

The Kriegstein lab has been studying the potential role of oRGs in the expansion of the human cortex for nearly a decade, "so it was particularly exciting to discover a molecular pathway in these cells that appears to have been specifically targeted during evolution and may help explain their specialized role in generating the advanced human cortex," Bhaduri said.

Tantalizingly, problems with mTOR signaling have also been linked to autism and other uniquely human neurodevelopmental disorders, suggesting new questions about whether pathways involved in the relatively recent evolution of our unusually large brains play some special role in these disorders.

For his part, Pollen says he has been working towards these experiments for more than a decade, since he was an undergraduate researcher studying the evolution of cichlid fishes in Tanzania's Lake Tanganyika, just miles from Jane Goodall's famous chimpanzee research station at Gombe Stream National Park.

"Being so close to wild chimpanzees made me want to ask questions about our own species' evolution," Pollen said. "But first we needed genomes, stem , and single-cell RNA sequencing to be able to understand the evolutionary programs that drive brain development in the two species. All of these things have since fallen into place, letting us address these long-standing questions more precisely than ever before."


Explore further

Differing division rates of brain stem cells

More information: Alexa A Pollen et al. Establishing Cerebral Organoids as Models of Human-Specific Brain Evolution. Cell. Published: February 7, 2019. DOI: 10.1016/j.neuron.2019.01.027
Journal information: Cell

Citation: Chimpanzee 'mini-brains' hint at secrets of human evolution (2019, February 8) retrieved 18 September 2019 from https://phys.org/news/2019-02-chimpanzee-mini-brains-hint-secrets-human.html
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Feb 09, 2019
Unfortunately the Chimpanzee brain has also been evolving the whole time... so it doesn't give us a window on the past at all. It shows us what 7 million years of parallel evidence produces.

Feb 09, 2019
"Identifying what drove this evolutionary shift is fundamental to understanding what makes us human, but has been particularly challenging for scientists because of ethical prohibitions..."

-against admitting the reality of tribalism and all its ramifications.

Tech drove overpopulation which resulted in tribes... protohumans who banded together in ever-larger groups to secure and defend resources.

"The basic cause of war is rivalry. And Ferguson sees positive value in it, where Hobbes had seen only a necessary evil. Ferguson points out that warfare enforces civic unity, engenders civic virtue, promotes social organization, and in fact may be an essential condition for the very existence of civilization (Dawson, 1996).
In addition to maintaining the balance-of-power between societies, Ferguson ascribes to warfare the function of maintaining solidarity and morale within societies. In-group amity depends upon out-group enmity and vice versa."
Cont>

Feb 09, 2019
Group selection began choosing ever larger and more cohesive tribes. The increasing complexities of tribal living created pressures to behave in very unnatural ways, such as sacrificing personal well-being, repro rights, and even life itself for the greater good.

Our brains grew in response. Individuals with greater capacity to communicate more complex information, to grasp more abstract ideas, and to both remember the past and imagine possible futures - these are the ones who would survive the rigors of tribal living and reproduce.

Conquering tribes would kill or enslave all the males of the vanquished and incorporate the females, thereby accelerating the evolution of bigger brains.

This was the path that created the first domesticated ape. Tribalism is ingrained in our genetic structure. It dictates our social structure and social interaction. It easily explains our history in very uncomfortable ways and threatens to unravel the artifice of our conditioning.

Feb 09, 2019
Unfortunately the Chimpanzee brain has also been evolving the whole time... so it doesn't give us a window on the past at all
It shows us where we would be without technology, chronic overpopulation, and tribalism.

Feb 09, 2019
Unfortunately the Chimpanzee brain has also been evolving the whole time..

Stuff doesn't evolve 'just because time passes' . Stuff evolves under environmental pressures.

There's loads of stuff around (some fungi, viruses, plankton, .. ) that hasn't changed much in the past billion years or so - just because it works so well that there hasn't been enough environmental pressure for it to need to adapt.

Feb 09, 2019
Interesting pieces to the particular puzzle.

Unfortunately the Chimpanzee brain has also been evolving the whole time... so it doesn't give us a window on the past at all. It shows us what 7 million years of parallel evidence produces.


What on Earth are you talking about? Not biology in any case. It is trivial that the similarities help us reconstruct the common ancestor, and the individual lineage differences the individual evolution. Of course it becomes more uncertain since no reconstruction can be exact, but it is a far cry from saying that it gives no information at all. This is Biology 101.

Group selection began choosing ever larger and more cohesive tribes.


It seems to me you mean a racial construct; that is unlikely to have been an important factor in the human lineage and no factor in the chimp lineage.

- tbctd -

Feb 09, 2019
- ctd- Reversely, if you mean aggression between groups which can be severe in some chimp groups but not all, and rare in humans, that too is unlikely to have affected chimps much.

"Group selection" has never been observed and deemed unlikely to be so by most biologists for that and for theoretical reasons (more unlikely and less pervasive than "selfish" gene selection), it is a fringe concept.

Feb 09, 2019
no factor in the chimp lineage
I was talking about humans re the first sentence in the article:

"At some point during human evolution, a handful of genetic changes triggered a dramatic threefold expansion of the brain's neocortex"

-Tribalism. Mystery solved (200 years ago.)
and rare in humans
Are you serious???

"Tribalism implies the possession of a strong cultural or ethnic identity that separates one member of a group from the members of another group. Based on strong relations of proximity and kinship, members of a tribe tend to possess a strong feeling of identity. Objectively, for a customary tribal society to form there needs to be ongoing customary organization, enquiry and exchange. However, intense feelings of common identity can lead people to feel tribally connected."
Cont>

Feb 09, 2019
"Challenges like war and crowding fostered among conquering races qualities of social cohesion, mutual aid, inventiveness in artifacts and weapons, economic specialization and human differentiation: "From the very beginning the conquest of one people over another has been, in the main, the conquest of social man over anti-social man; or, strictly speaking, of the more adapted over the less adapted" (1851, p. 455; Cf. Bagehot)
http://rint.recht...rid2.htm

-Ive posted quotes from this essay many times. If you think you have valid objections to what I'm saying you ought to at least read it in its entirety.

Feb 09, 2019
Group selection" has never been observed and deemed unlikely to be so by most biologists for that
Group selection is such a taboo topic that lots of mainstream academies refuse to touch it. Tribalism is unique to the human species although it has many natural analogues. Goodall observed intergroup warfare among apes. Worker bees have surrendered their repro rights for the good of the tribe.

But it is only with human influence that we can use the term domestication. We have domesticated plants and animals to serve us. The tribe has domesticated the human ape to serve IT.

"Self-domestication theories describe how humans developed and evolved."
https://en.wikipe...tication
Cont>

Feb 09, 2019
"Gregory Stock, director of the UCLA School of Medicine's Program of Medicine, Technology and Society, describes self-domestication as a process which "... mirrors our domestication [of animals] ... we have transformed ourselves through a similar process of self-selection ... our transformation has been primarily cultural [read tribe], but it has almost certainly had a biological component."

"The most comprehensive case for human self-domestication has been proposed for the changes that account for the much later transition from robust humans such as Neanderthals or Denisovans to anatomically modern humans."

-And theres plenty of evidence

"a statistically significant number of genes associated with domestication which overlapped between domestic animals and modern humans, but not with their wild equals, like Neanderthals"

-I can keep throwing quotes at you but unless you read their sources (a few wiki pages and the rechten essay) then you have no argument.

Feb 09, 2019
Group selection" has never been observed and deemed unlikely to be so by most biologists for that and for theoretical reasons (more unlikely and less pervasive than "selfish" gene selection), it is a fringe concept
I see you have done a little reading...

"Dawkins suggests that group selection fails to make an appropriate distinction between replicators and vehicles.[57]

"The psychologist Steven Pinker concluded that "group selection has no useful role to play in psychology or social science"

-Again, the idea that humans emerged as a result of millenia of larger and more cohesive tribes systematically wiping out the competition and impregnating all the females, is a little hard for these guys to swallow. And also outside their disciplines.

Selfish genes know when the best way to propagate is to band together with other 'vehicles' to ensure their survival. IOW the ones that failed to do this were the ones that died out. Slaughtered and consumed. Ground into dust.

Feb 10, 2019
Are you serious


Yes, Humans are relatively peaceful, and you provide no reference to "tribalism" effects under millions of years of evolution.

Group selection is such a taboo topic


Are *you* serious? We discussed group and other selection in basic biology courses at university; it is not taboo but as I said found to be not happening; your own quotes allude to that fact.

And again you give no references supporting group selection. Maybe I should read you as confused by what it means, since you start to discuss self-domestication and gene-level selection.


Feb 11, 2019
Yes, Humans are relatively peaceful, and you provide no reference to "tribalism" effects under millions of years of evolution
This is like saying that lions or raccoons or dogs are relatively peaceful. Any animal can be expected to fight like hell when cornered or its family is threatened.

Due to the FACT that humans have been using tech for a million years to systematically eliminate the natural attritive elements from their environment, the FACT is that overpopulation has always been a problem. It forced humanity to band into tribes for survival. And tribes have been fighting ever since.

It's what caused the rapid and thorough spread of our species around the globe and into every possible niche no matter how inhospitable.
discussed group and other selection in basic biology courses
-And I bet you discussed such crap as tabula rasa as well.

Academies - their job is to mold and shape human opinion and behavior, not explain it. Domestication is ongoing.

Feb 11, 2019
And again you give no references supporting group selection
The greatest legend ever told, was about group selection. God gave the 12 tribes the right to invade the holy land and cleanse it of canaanites, philistines, and the lot.

More recently the bantu tribes set out to claim their holy land from the khoisan, who would have been exterminated without western intervention. Any natural evolutionary advantages they had accrued would have been lost.

Iroquois, with western help, chased the huron north to an island in the great lakes and exterminated them. And then the west exterminated the iroquois. Western influence was for them both a very unnatural evolutionary advantage and a detriment.

Where did the Basque come from? All related tribes exterminated. Tribe after tribe overrun, obliterated, enslaved, their women absorbed, their genes added to the amalgam.

Our history is nothing BUT a record of intertribal conflict, which is the human form of group selection.

Feb 11, 2019
The recent Rwanda/Burundi genocides. Tutsi and hutu tribes, among the highest fertility rates in the world. Evidence says they were originally a single people, driven apart by the age-old herder/grower conflict as immortalized in the cain/abel fratricide, the first murder... and by nefarious euro machinations.

Classic intertribal warfare, driven by explosive population growth and subsequent shortages of land and resources.

Countless examples throughout all of history, including the history we have gleaned form innumerable hunter gatherer tribes around the globe.
Cont>

Feb 11, 2019
What makes you think that this wasnt common throughout the pleistocene?

"So why were the people of Nataruk attacked? We have to conclude that they had valuable resources that were worth fighting for – water, meat, fish, nuts, or indeed women and children. This suggests that two of the conditions associated with warfare among settled societies – territory and resources – were probably common among these hunter-gatherers, and that we have underestimated their role so far."

-Academies wanted us to believe that maya and Aztec were peaceful, innocent people until undeniable evidence of their bloodthirsty savagery was unearthed.

"Maori Warriors were some of the fiercest warriors the world has ever known. Their bravery and savageness are legendary. Throughout their history war was a part of Maori life. Conflicts over land and insults of any type were the main catalyst for war."

-new guinea cannibals, Sentinelese murdering outsiders, inuit slaughtering vikings. The norm.

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