What does it take to get Carl Zimmer to review your research in the New York Times?
I suppose it helps to be at Harvard. It also helps to have a combination of subjects — evolution and the human brain — that Zimmer has written about in the past. It helps to have a paper with lots of very pretty diagrams — the authors’ hypothesis is professionally illustrated. It’s also a good idea to have a vast sweeping explanation for the exceptionalism of the human brain. In this case, they call it the Tethering Hypothesis, and it’s supposed to explain how humans evolved all these remarkable cognitive abilities.
The human cerebral cortex is vastly expanded relative to other primates and disproportionately occupied by distributed association regions. Here we offer a hypothesis about how association networks evolved their prominence and came to possess circuit properties vital to human cognition. The rapid expansion of the cortical mantle may have untethered large portions of the cortex from strong constraints of molecular gradients and early activity cascades that lead to sensory hierarchies. What fill the gaps between these hierarchies are densely interconnected networks that widely span the cortex and mature late into development. Limitations of the tethering hypothesis are discussed as well as its broad implications for understanding critical features of the human brain as a byproduct of size scaling.
You know what you don’t need? Data, or a hypothesis that makes sense.
The paper is largely a review of neuroanatomy, describing features of the human brain that we’ve known about for a long, long time…except now we can illustrate them with lovely color diagrams and fMRI scans. Here’s an illustration of the problem in human evolution:
There are areas of the brain that we know what they do: in red, for instance, is the primary somatosensory cortex, which is a map of muscles and sensory areas on our skins, while blue is the primary visual cortex, which is where information from our eyes is processed. In between these known areas are great beige unknowns — regions of the brain called association cortex, which integrate information from various other regions in complex ways. Our primary somatosensory and visual cortices aren’t much bigger than those of a chimpanzee, which makes logical sense, since there isn’t much difference in surface area or visual acuity between us, and most of the growth has occurred in the association cortex.
All well and good. The question is, what made our association cortex expand in our evolution, and how is that expansion related to specific human intellectual capacities? Those are good questions, and I’d be curious to see them answered. Too bad this paper doesn’t.
One problem is that it is a review paper and really doesn’t test anything — it catalogs some existing knowledge about brain organization and then throws out this Tethering Hypothesis to explain it all, which it doesn’t. I do like the fact that it suggests that most of our abilities are spandrels, not explainable as adaptations, and that what it proposes is that novel abilities arose from regions of the brain that were not constrained by ancestral functional requirements. I just don’t see how their mechanism explains that.
Here’s one short paragraph from the paper that neatly summarizes their hypothesis.
The idea of some form of radiation outward from core organizing centers is appealing because the hominin cerebral cortex vastly expanded in a short time. It seems implausible that molecular gradients could emerge fast enough to specify new cortical areas, although developmental expression patterns have clearly been modified. Building from Rosa and colleagues’ ideas about visual cortex organization, we propose a more general tethering hypothesis to explain how new features of cortical organization might have emerged during the rapid evolutionary expansion of the cerebral mantle. The word ‘tether’ is used to emphasize that the expanding cortical plate is tethered to gradients that initially evolved in a cortex with a far smaller surface area. Much as taffy, being pulled apart, thins until it breaks in the middle, the expanding cortical zones far from the strong constraints of developmental gradients and sensory input may become untethered from the canonical sensory–motor hierarchies.
OK, that begs the question: why did the hominin cerebral cortex expand in the first place? They keep talking about this “expanding cortical plate”, but not why it was expanding or why it necessitates new organizing centers. The taffy metaphor is also telling; why are they talking about things being pulled apart, when expansion of the brain is not caused by external forces pulling on it, but on internal forces of growth generating more tissue between known cortical zones?
I’m also put on edge by the phrase “It seems implausible that…”, especially when applied to something that doesn’t seem implausible at all. Why balk at a timescale of several million years to evolve a use for a bit of extra brain matter?
But even worse, nervous systems growing bigger is what I study. My Ph.D. research was on connectivity in the developing spinal cord of zebrafish, for instance.
The first neurons in the zebrafish embryo emerge at about 18 hours after fertilization, at a time when the nascent spinal cord is about 2mm long, in total. Cells in the hindbrain send axons all that distance (2mm is a long way in an embryo!), and as they grow, they make a little knot of synapses every 40-50µm with cells called primary motoneurons.
That’s in the embryo. In the adult, the spinal cord is roughly 4cm long — there’s been a 20-fold expansion in size. What do you think happened to that earlier array of cells? Did the system stretch and break?
No, it grew. In the adult, the same hindbrain neurons are still present, and their axons still reach all the way back to the tailtip. And the same motoneurons are still present, they’re just spread out more to be separated by 1-1.5mm, and they still retain the same synapses.
I also did research on the earliest neurons to differentiate in the grasshopper nervous system. I studied Q1, a neuron that established one of the commissures in the grasshopper ganglion. That story is a little different: Q1 doesn’t seem to have any function in the adult, and in fact looks to be abandoned and gone. But what it does is send the first slender thread across on a specific pathway; it pioneers a route across the nervous system, and then other axons pile on and follow it across. It’s like sending a kite string across a chasm, then using the string to pull a rope across, and then using the rope to pull a cable across, and pretty soon you’ve got a bridge — and it’s doing this as the chasm is widening, because like the zebrafish, the grasshopper is also growing substantially during these events.
Growth is an integral process in the development of the nervous system. Without specific evidence that these developmental mechanisms break down during growth (which seems implausible to me…), why would you postulate that a failure of developmental processes was an essential element of human evolution? A tripling of brain size from the human-chimpanzee common ancestor to the modern human seems like a small shift relative to the much larger expansion of the human fetal brain to the adult brain.
What I’d like to see, and did not find in this paper, are comparative developmental studies. When these various cortical regions of the brain are specified or establishing connectivity, how far apart are they in different species? Compare mouse and rat, for instance, or rhesus monkey and human. I suspect that in early embryos, the distances, and their relative differences, will be minuscule, and that signaling centers will be close enough that it will seem silly to argue that broad patterns of connectivity would be unable to form in the biggest brains, leaving gaps that need to be filled in by novel mechanisms and structures.
But again, the paper doesn’t look at any of that at all. I found one paragraph that briefly discusses other observations that association cortex matures later than other regions of the brain, and that’s about it — it is definitely not sufficient information to argue that association cortex is out of reach of intrinsic signaling gradients in the early brain.
At least the first subtitle in the paper is “A Speculative Hypothesis,” which is entirely accurate. I don’t see how it justifies the praise it was given in Carl Zimmer’s article.
Dr. Sherwood, the George Washington University expert, praised the hypothesis for being “fairly frugal.” The emergence of the human mind might not have been a result of a vast number of mutations that altered the fine structure of the brain. Instead, a simple increase in the growth of neurons could have untethered them from their evolutionary anchors, creating the opportunity for the human mind to emerge.
Oh, wait. When the best thing you can say about a hypothesis is that it is “fairly frugal”, that’s not much praise at all.
Buckner RL, Krienen FM (2013) The evolution of distributed association networks in the human brain. Trends Cogn Sci 17(12):648-65.
This will be useful shorthand. You may recall that Alec Baldwin lost his show for calling a photographer a “cocksucking faggot” — now Geraldo Rivera weighs in on the phrase.
SKLAR: When I heard about what Alec Baldwin – Alec Baldwin had a history of making these homophobic slurs.
RIVERA: That wasn’t a homophobic slur.
SKLAR: Okay –
RIVERA: I mean if you grew up where we grew up –
SKYLAR: And yet he is no longer on the network, right?
RIVERA: Sean, Baldwin and I all grew up within ten miles of each other and when we were growing up, in my year especially, those comments were commonplace.
Remember that next time someone strolls in and starts flinging the “cunt” insult around, and tries to excuse it because it was commonplace when they were growing up in Australia or England or New Jersey or wherever. Just let them know they’re using Geraldo Logic, and with any luck they’ll feel a twinge of shame.
Nah, they won’t. We know from long experience that they won’t.
An interesting philosophy paper: ‘That Man Behind the Curtain’: Atheism and Belief in The Wizard of Oz. I don’t think the movie The Wizard of Oz is exactly an atheist movie, but represents the current transition we’re experiencing, where the old-fashioned beliefs are becoming increasingly untenable and unsupported by the culture as a whole, while people are still largely uncomfortable with abandoning the traditional big guy in the sky.
This decaffeinated belief—this belief without belief—is everywhere in The Wizard of Oz, even in the film’s conclusion. When Dorothy finds herself back in Kansas, she tries to tell her family about her voyage, but Aunt Em silences her, saying, ‘You just had a bad dream.’ Dorothy replies, ‘But it wasn’t a dream. It was a place.’ When she tells the farmhands and Professor Marvel that they were all there, they laugh. Aunt Em tries once more to convince Dorothy that she has been dreaming, but Dorothy protests: ‘No, Aunt Em. This was a real, truly live place.’ As she continues to describe her experience, she is again met with laughter. But when she indignantly asks the central question—‘Doesn’t anybody believe me?’—Uncle Henry responds by saying, ‘Of course we believe you, Dorothy.’ Her family and friends offer a kind of ‘decaffeinated belief’. They do not really believe her, of course, but they do not wish to shake her faith. Believing in belief, they allow her to maintain her delusional inner conviction that Oz is real.
It is worth noting that ‘decaffeinated belief’ has likely been around as long as belief itself; similarly, belief in abstract (rather than anthropomorphic) deities certainly pre-dates the modern era. (One thinks of the connection made between God and the Word in the opening verse of John, for example; or later, Spinoza’s move toward a kind of pantheism.) Nevertheless, Žižek and Dennett are correct to suggest that various forms of diluted belief have taken on special force in modern times. It has been difficult for many (particularly in the especially religious United States) to come to terms with the serious challenges to the supernatural offered by Darwin, Marx, and Freud. When Hegel and Nietzsche declared the death of God, believers scrambled to put God on life support, re-defining ‘God’ in abstract ways to make belief seem more defensible. Few intellectuals could still argue for traditional conceptions of God in the post-Darwin era (for example, God as a divine watchmaker, pace William Paley), but belief itself refused to become extinct; God mutated into more arcane, abstract notions in order to survive the skeptical spirit of modernism. It is this simultaneous loss of belief and maintenance of belief in the modern era that is captured perfectly in Victor Fleming’s The Wizard of Oz.
There are lots of little bits throughout the movie that give the game away — which never really jumped out at me because I take their attitude for granted. Now I might just have to watch the whole thing again sometime to look for them. Also, flying monkeys are just cool.
Raif Badawi has already been sentenced to seven years in prison and 600 lashes, and now he has been recommended to be be brought before a high court on a crime that carries the death penalty. All for having a remarkable resemblance to Tom Hiddleston.
No, wait, it’s for an equally trivial crime: he founded a blog network that is critical of political and religious figures, he disobeyed his father (he is 31 years old), and he does not believe in god. Ed Brayton better watch out.
One of his great crimes is that he once wrote about Valentine’s Day, a prohibited holiday in Saudi Arabia.
This is what theocracy takes us to. And Saudi Arabia is one of our allies? Shouldn’t we have better taste in friends?
Here’s a petition.
The pope has included (nominally) atheists in his Christmas message.
He proved unpredictable again on Wednesday, when he went off script to include atheists in his call for peace, rare for a Catholic leader.
“I invite even nonbelievers to desire peace,” he said. “Let us all unite, either with prayer or with desire, but everyone, for peace.”
Speaking for myself…NO. I turn my back on this pope and any other.
I believe strongly that how you arrive at a conclusion is just as important as the conclusion itself; I care about the process, because even a flawed method will give you an answer — you just don’t know whether it is right or not. I can agree with the pope that peace is a desirable end, but I only happen to agree with him this time. I probably won’t agree with him on just about any other subject, and I can’t trust how he arrived at this mutually copacetic idea.
I also disagree on the nature of the peace he is looking for. The Catholic church desires the peace of ignorance, the peace of acquiescence, the peace of unquestioning acceptance of a dogma calibrated for fools. No, thanks. Give me the kind of peace where dissent can thrive and knowledge grows and ideas can change.
The pope can join in the quest for peace as a fellow human being, but he is not a leader and he is not representative of humanity in any way, and the media attention on his toothless pronouncements is unseemly. I also don’t want to live under a peace that allows misogyny to thrive and lets child rapists roam free and thinks fetuses are more precious than women. This pope is not my friend nor my ally.
I want to live in a world in which it is not sufficient for a clown to get a prestigious position by bowing to an arcane hierarchy, and then gets a lot of fawning friends, even among atheists who ought to know better, because he is glib about preaching platitudes. I’m not taken in by the smiling façade plastered over the goddamned Catholic Church.
Don’t forget what this man represents, even when he kisses you on the cheek, atheists.
Of course the plant for today has to be a Christmas tree. A big dead tree.
This one is going to be milled into lumber and donated to Habitat for Humanity, which is nice for humanity I guess. Not so cool for the tree.
I’m pretty comfortable here, waiting for the kids to get up and open their presents, last night we had a pleasant evening with a vegan dinner with mead, and later today we’re getting on a plane and heading back home, so I’m too mellow right now to write something ferocious. For that, I recommend reading this article which I heartily endorse: Burn the Fucking System to the Ground.
I’m indulging in a little personal complacency today, but never forget: America is screwed up.
I’m on a search committee for a tenure track position in statistics and computer science — we’re looking for someone to teach a data science course, maybe a little bioinformatics on the side, and work with both our statistics and computer science disciplines. I’m the outside member of the committee — you know, the weirdo who isn’t steeped deeply in the culture of the disciplines and maybe is better able to provide the big picture perspective on how candidates will fit with the rest of the university — so I know next to nothing about this stuff. My eyes were crossing and my brain was breaking as I reviewed candidate applications. What I really needed was this bingo card. I think I saw all of those terms fly by as I was flipping through CVs and research and teaching statements.
Don’t worry, I deferred to the expertise of my colleagues on all matters dealing with the details of their work.
It’s always interesting, though, to peek into the domains outside my own, and feel a little humbled at all the stuff I don’t know.