Most of you have probably seen this stylized graphic somewhere along the away (I think it was on PBS at some point). But it’s still cool….
Most of you have probably seen this stylized graphic somewhere along the away (I think it was on PBS at some point). But it’s still cool….
I really love the fact that I live in the early 21st century for a host of reasons. That being said, one aspect that’s certainly true is that when it comes to charismatic natural variety and geography there are very few “blank spots” on the map. You can get a sense of what I’m talking about if you browse National Geographic from the early 20th century. Most of the map had been filled in, but there were still nooks and crannies waiting to be illuminated. So I always find stories like this interesting, because they capture a sliver of the wonder that once was so commonplace, Snow Leopard Population Discovered in Afghanistan:
The Wildlife Conservation Society has discovered a surprisingly healthy population of rare snow leopards living in the mountainous reaches of northeastern Afghanistan’s Wakhan Corridor, according to a new study.
The Wakhan Corridor in northeast Afghanistan is an area known for relatively abundant wildlife and it appears to represent Afghanistan’s most important snow leopard landscape. The Wildlife Conservation Society (WCS) has been working in Wakhan since 2006. Recent camera trap surveys have documented the presence of snow leopards at 16 different locations in the landscape. These are the first camera trap records of snow leopards in Afghanistan. Threats to snow leopards in the region include the fur trade, retaliatory killing by shepherds and the capture of live animals for pets. WCS is developing an integrated management approach for this species, involving local governance, protection by a cadre of rangers, education, construction of predator-proof livestock corrals, a livestock insurance program, tourism and research activities. This management approach is expected to contribute significantly to the conservation of snow leopards and other wildlife species in the Wakhan.
In the comments below Antonio pointed me to this working paper, What Do DNA Ancestry Tests Reveal About Americans’ Identity? Examining Public Opinion on Race and Genomics. I am perhaps being a bit dull but I can’t figure where its latest version is found online (I stumbled upon what looks like another working paper version on one of the authors’ websites). Here’s the abstract:
Genomics research will soon have a deep impact on many aspects of our lives, but its political implications and associations remain undeveloped. Our broad goal in this research project is to analyze what Americans are learning about genomic science, and how they are responding to this new and potentially fraught technology.
We pursue that goal here by focusing on one arena of the genomics revolution — its relationship to racial and ethnic identity. Genomic ancestry testing may either blur racial boundaries by showing them to be indistinct or mixed, or reify racial boundaries by revealing ancestral homogeneity or pointing toward a particular geographic area or group as likely forebears. Some tests, or some contexts, may permit both outcomes. In parallel fashion, genomic information about race can emphasize its malleability and social constructedness or its possible biological bases. We posit that what information individuals choose to obtain, and how they respond to genomic information about racial ancestry will depend in part on their own racial or ethnic identity.
We evaluate these hypotheses in three ways. The first is a public opinion survey including vignettes about hypothetical individuals who received contrasting DNA test results. Second is an automated content analysis of about 5,500 newspaper articles that focused on race-related genomics research. Finally, we perform a finer-grained, hand-coded, content analysis of about 700 articles profiling people who took DNA ancestry tests.
Three major findings parallel the three empirical analyses. First, most respondents find the results of DNA ancestry tests persuasive, but blacks and whites have very different emotional responses and effects on their racial identity. Asians and Hispanics range between those two poles, while multiracials show a distinct pattern of reaction. Second, newspaper articles do more to teach the American reading public that race has a genetic component than that race is a purely social construction. Third, African Americans are disproportionately likely to react with displeasure to tests that imply a blurring of racial classifications. The paper concludes with a discussion, outline of next steps, and observations about the significance of genomics for political science and politics.
Survey results are fine and good, but the public reception and interpretation of genomics is being created anew right now. I spend some time on the best way to gain some insights from ADMIXTURE and PCA because I don’t want to confuse people myself. Most of the reactions have been pretty banal. It turns out that Latin Americans under the presumption that they are “pure Spanish” are not always “pure Spanish.” White Americans yearning for Native American ancestry often have their hopes dashed. White Americans who dismissed the family history of a part-Native American grandparent due to the romanticism about aboriginal blood which they perceived around them, turn out to be part-Native American.
People do have confusions that need to be cleared up, but it isn’t like academics are going to give them that much insight. I know that the above is a working paper, but here’s a sentence that crept into that text: “…Hispanics are mestizo more or less by definition….” No, Hispanics are very specifically constructed as a race-neutral term in the USA. Obviously many Hispanics from the Caribbean also don’t self-identify as mestizo. Honestly, do the authors know any Hispanics?
So what has your experience been with scientific genealogy? I’ve already talked about my own personal journey at length. I think that race as a concept does have biological utility, but the biggest question mark which I move forward with is how oral history can diverge so rapidly from what our genomes tell us. In particular, the tendency to anchor on slices of privileged ancestry. Looking at it every which way I have confirmed to my satisfaction that my mother does have a small, but detectable, amount of Middle Eastern ancestry from her maternal grandfather as the oral histories and textual records tell us. But this dwarfed by a component she shares with my father which ties them to eastern Asia. But neither are aware of any such connection. These are ancestors forgotten, and makes me reflect on how recollection of memes is not always a remembrance of genes. This may not be as sexy an issue as reification of race through personal genomics, but to some extent that issue is so 20th century. Hundreds of thousands are people are just marching ahead into the future, no matter how “fraught” the results generated by obscure algorithms may seem.
I’ve been taking about ‘meat things’ for nearly 10 years, so I was really excited by the new Michael Specter piece in The New Yorker about artificially grown meat, Test-tube Burgers. You can’t read most of it online, so I want to copy this small section:
…One study, completed last year by researchers at Oxford and the University of Amsterdam, reported that the production of cultured meat could consume roughly half the energy and occupy just two percent of the land now devoted to the world’s meat industry….
I say real factories because we are all aware I assume by this point of the nature of ‘factory farming’. But mass production of animal stock is an ad hoc kludge. Domesticated animals have been bred for meat production, but they remain organisms with all the range of activities and ends which the term ‘organism’ entails. Raising raw tissue in cultures may seem ‘yucky,’ a point Specter covers in assessing the reaction of some environmentalists and animal-rights activists who don’t seem as excited by the shift from conventional livestock raising to growing tissue as one would expect if they ran the numbers, but it is probably inevitable if it is feasible. The article makes the point that most of the focus on this area seems to be in the Netherlands, but thank god the Chinese are paying attention to this!
On DNA Day, 23 and Me had a sale on their personal genomics service. They’d do their standard scan of your genome for free, as long as you paid for a year’s worth of their online subscription service.
For the price (nearly free up front, and a modest cost for the online community provided), my wife and I jumped on the deal. Since I got the results back two weeks ago, I’ve been exploring not only the services and information provided by 23 and Me, but the various other tools that individuals have started producing to help analyze and investigate this insight into my ubiquitous but invisible DNA.
My genome, for instance, revealed a genetic predisposition towards late-onset Alzheimers. The odds of getting Alzheimers are still quite small, but elevated because of this particular mutation to the APOE4 gene. This wasn’t a total surprise, given my family history, and as a healthy, young guy with a background in biology and biostatistics, it wasn’t hard for me to put that information into a context and move on. Down the road, I’ll probably keep an eye out for new research on Alzheimers medicines and look into tools for early detection, but I’m not going to kill myself if I forget my keys. (Thanks to the federal Genetic Information Nondiscrimination Act and the Affordable Care Act’s prohibition on “pre-existing conditions” – not to mention the inherent uncertainties in translating this genetic result to a specific outcome – I’m not especially worried about discussing that result in public)
We need to demystify DNA. It’s pretty obvious to me that people perceive genetics to be in the domain of magic, when in reality it manifests itself in the banal realities of correlations within the family, which we’re intuitively aware of. But Josh’s post is more than just personal, he reviews the book Biopunk: DIY Scientists Hack the Software of Life:
Most of the biopunks Wohlsen introduces us to aren’t trying to cure diseases or create genetic tests. They surely wouldn’t mind if they changed the world somehow, but their interest in DIY biology is driven more by a sense of personal exploration and a pure fascination with how things work. The goal, one of these biopunks explains, is to “increase the tinkerability” of biology, “simplifying and domesticating” it to make it accessible to anyone who wants to play with it. Groups like the Bay area’s Biocurious aim to create communal molecular biology labs which anyone can join and tinker in; Biocurious will open its lab this summer in Mountain View, not far from Google and the researchers at NASA’s Ames facility.
But I’m also fascinated because this is the future even for people whose aversion to biochemistry is even greater than my own. Just as everyone in the mid- to late 20th century needed some grasp of physics to be able to think sensibly about nuclear energy, nuclear war, and a host of related issues, the 21st century is sure to be dominated by biology. And DIYbio can play a key role in democratizing science, precisely because it’s more focused on what’s neat than on what’s likely to turn up a new Nobel Prize or a new patent and venture funding for a biotech startup. Its openness will be a great strength as a tool for improving science literacy, and biopunks know it.
I obviously support this movement and its intents (I’ve met a few of the people who are prominent in it). But we need to keep perspective here. This will probably be analogous to the free or open source software movement; the base of tinkers will be much larger than corporations and academic institutions, but it isn’t going to expand to cover the majority of the public. But so what? Most us can probably agree that the ad hoc decentralized elements of the software engineering community have done good just by putting pressure on the margins of staid institutions. Similarly, a minority of biology enthusiasts and hobbyists are going to shape the production and consumption of the plethora of new products we’re going to see coming online within the next few decades. There is often someone in the family who you turn to for tech advice. Now there may be someone in the family who you turn to for personal genomics advice. This is the democratization and decentralization of specialization!
When it comes to the mass consciousness aspect I think personal genomics and other consumer biotech will play a large role in demystifying DNA, and in the future making the public more open to the possibilities of bioengineering. Those of us alive today are on the cusp of a new age. I think the medium-term shape of that age is highly sensitive to initial conditions, so we should be both hopefully and vigilant.
The title above basically describes the message of evolutionary biologist Mike Lynch from what I can gather. His basic argument is outlined in long form in The Origins of Genome Architecture, though the outline of the thesis is evident over 10 years back (see Preservation of Duplicate Genes by Complementary, Degenerative Mutations). Verbally I think the easiest way to explain Lynch’s framework is that in species with small effective population sizes the creativity of stochastic forces in generating non-adaptive structure and complexity tends to overwhelm the power of natural selection to prune this tendency toward baroque. I reviewed a paper last year which argued that Lynch’s observation of an inverse relation between effective population and genome size was an artifact, that once you controlled for phylogenetic history it disappeared. Suffice it to say this is an area of dispute and active research, so we shouldn’t take any individual’s word for it. This is science on the broadest canvas. Extraordinary general claims need to backed by a generation of publication I’d think.
Lynch is now a co-author on a new letter to Nature (which is open access, so read it!), Non-adaptive origins of interactome complexity. Imagine if you took biochemistry, specifically the nearly impenetrable language of protein interactions, and crossed it with evolutionary genomics. This is what you’d get.
Why does interactome complexity matter? Let me quote from the abstract : “This leads to the hypothesis that the accumulation of mildly deleterious mutations in populations of small size induces secondary selection for protein–protein interactions that stabilize key gene functions. By this means, the complex protein architectures and interactions essential to the genesis of phenotypic diversity may initially emerge by non-adaptive mechanisms.”
You probably know about neutral theory, whereby most evolution on the molecular level is due to substitutions which have neither positive nor negative selective effects. That is, they’re not adaptive. A related model is the nearly neutral theory, where a substantial fraction of substitutions are ever so mildly deleterious. So mild in fact that selection does not “see” these mutations as harmful enough to “purge” them from the genome. This is related to effective population size, which measures the proportion of individuals which matter for purposes of genetics in a set of individuals (if a population is 100, but only 10 breed, then there’s a huge difference between census and effective population size). As effective population size declines the power of random genetic drift becomes more evident. This is simply sample variance, which converges upon zero as N approaches infinite. If you flip a coin 100 times you will expect it to deviate proportionally from expectation (0.50 of both sides) more than if you flipped the coin 1000 times. Low effective population sizes are like the swell of noise against which natural selection is attempting to “make music.”
In this paper the authors seem to be suggesting that these broader population genetic dynamics result in suboptimal functionality on the molecular level as deleterious mutations build up. Complex molecular interactions then emerge through secondary natural selection pressures as a way for the whole Rube Goldberg system from collapsing in on itself. Wheels within wheels. The implication then is that complex organisms evolved not because they were better in a reproductively fit sense in relation to simple organisms, but that organismic complexity is simply a way for collections of simple organisms to not fall apart when subject to stochastic forces which increase the mutational load.
Back in the day my background was in biochemistry, but there’s a reason that I don’t talk about it much in this space. I’m not too excited about the prospect of visualizing the shape and character of a protein and its various subunits (I should have realized something was up when I found that I preferred physical chemistry to biochemistry!). But I’d be curious about the impression of readers who are versed and fluent in the biochemistry to evaluate the claims within. After the criticism of the genome size – effective population size correlation I’m a touch wary about an argument which relies on just 36 species. I also haven’t totally given up on the idea that one could introduce a fitness landscape model here, where organism complexity may initially have been a response to suboptimal fitness, but that after crossing the fitness “valley” the species could then ascend a new “peak.”
Citation: Ariel Fernández, & Michael Lynch (2011). Non-adaptive origins of interactome complexity Nature : 10.1038/nature09992
John Hawks and Jerry Coyne are mooting the ‘species concepts’ debate, with particular focus on recent human origins (specifically, the relationship of modern humans to Neandertals and Denisovans). Coyne, who coauthored the book Speciation and remains preoccupied with the issue in his academic work, knows of what he speaks. And of course he wouldn’t think that the discussion of species, how to delineate them, and what they are, is a sterile exercise. He has chosen to allocate a significant portion of his life to the topic. I think very few would disagree with Coyne when he contends that “Species are not arbitrary divisions of an organic continuum.” If there is one taxonomic category which has a concrete basis in reality, that would seem to be species. But, I would observe that I’m not sure that species are necessarily so clear and distinct. After all, we know that there is here and there, but where does here end, and there begin?
I’m of a reminded of the classic Zeno’s paradox:
In the paradox of Achilles and the Tortoise, Achilles is in a footrace with the tortoise. Achilles allows the tortoise a head start of 100 metres. If we suppose that each racer starts running at some constant speed (one very fast and one very slow), then after some finite time, Achilles will have run 100 metres, bringing him to the tortoise’s starting point. During this time, the tortoise has run a much shorter distance, say, 10 metres. It will then take Achilles some further time to run that distance, by which time the tortoise will have advanced farther; and then more time still to reach this third point, while the tortoise moves ahead. Thus, whenever Achilles reaches somewhere the tortoise has been, he still has farther to go. Therefore, because there are an infinite number of points Achilles must reach where the tortoise has already been, he can never overtake the tortoise.
The Greeks had a fascination with paradoxes because they perceived that they illuminated deep truths about the true nature of reality which we may have been blind to via sense perception. But sometimes I think that a fixation on species as the taxonomic category to rule them all confuses and calcifies the understanding of evolutionary genetic processes in the eyes of the public. Just as it is difficult to communicate that science is not a collection of facts, that it is a process and a method, so many people seem to take species categorizations as reflecting the true order of the universe. Historically this goes back to the pre-evolutionary taxonomists whose aim was to catalog all of God’s creation. It persists today explicitly among Creationists, who bandy about terms like “kinds,” but are really talking about immutable ideal entities with particular essences. Species on steroids if you will.
A fixation on the species has also confused the public on the issue of microevolution vs. macroevolution. Creationists regularly accept the former and reject the latter, despite the fact that the majority of biologists would probably assert that evolutionary processes are a unified whole, with no difference of scale. The constant usage of the term “microevolution” by the enemies of evolution seems to have even cast that term into some disrepute, I’ll admit to be shocked when a reader was confused as to the non-Creationist usage when I recommended Alan Templeton’s Population Genetics and Microevolutionary Theory. One could argue that the subject of modern population genetics is fundamentally microevolution.
Species are obviously abstractions. But I think an analogy can be made between them and physical objects. At the end of the day we know that the solidity and boundedness of physical objects are perceptions and interpretations filtered through our brains. Fundamentally they’re a bundle of particles and forces, interacting with other particles and forces. We don’t need to deny this deep reality, all the while instrumentally acknowledging the usefulness of categories of physical objections.
This morning I received an email from the communication director of the American Anthropology Association. The contents are on the web:
AAA Responds to Public Controversy Over Science in Anthropology
Some recent media coverage, including an article in the New York Times, has portrayed anthropology as divided between those who practice it as a science and those who do not, and has given the mistaken impression that the American Anthropological Association (AAA) Executive Board believes that science no longer has a place in anthropology. On the contrary, the Executive Board recognizes and endorses the crucial place of the scientific method in much anthropological research. To clarify its position the Executive Board is publicly releasing the document “What Is Anthropology?” that was, together with the new Long-Range Plan, approved at the AAA’s annual meeting last month.
The “What Is Anthropology?” statement says, “to understand the full sweep and complexity of cultures across all of human history, anthropology draws and builds upon knowledge from the social and biological sciences as well as the humanities and physical sciences. A central concern of anthropologists is the application of knowledge to the solution of human problems.” Anthropology is a holistic and expansive discipline that covers the full breadth of human history and culture. As such, it draws on the theories and methods of both the humanities and sciences. The AAA sees this pluralism as one of anthropology’s great strengths.
Changes to the AAA’s Long Range Plan have been taken out of context and blown out of proportion in recent media coverage. In approving the changes, it was never the Board’s intention to signal a break with the scientific foundations of anthropology – as the “What is Anthropology?” document approved at the same meeting demonstrates. Further, the long range plan constitutes a planning document which is pending comments from the AAA membership before it is finalized.
Anthropologists have made some of their most powerful contributions to the public understanding of humankind when scientific and humanistic perspectives are fused. A case in point in the AAA’s $4.5 million exhibit, “RACE: Are We So Different?” The exhibit, and its associated website at www.understandingRACE.org, was developed by a team of anthropologists drawing on knowledge from the social and biological sciences and humanities. Science lays bare popular myths that races are distinct biological entities and that sickle cell, for example, is an African-American disease. Knowledge derived from the humanities helps to explain why “race” became such a powerful social concept despite its lack of scientific grounding. The widely acclaimed exhibit “shows the critical power of anthropology when its diverse traditions of knowledge are harnessed together,” said Leith Mullings, AAA’s President-Elect and the Chair of the newly constituted Long-Range Planning Committee.
As for the last paragraph, it illustrates the selectivity of a discipline which attempts to contextualize, and often has a skeptical relationship toward a positive framework. I believe that race is a social construct. The Hispanic identity, which consists of people of indigenous Amerindian, European, and African ancestry, and all their combinations, has been racialized. The Islamic identity has also been racialized. Benjamin Franklin stupidly contended that only the English and Saxons were true whites, with all other Europeans, including Nordics, being swarthy.
But just because a construct has a social element does not mean it has only a social construct. Because of the Left-liberal anti-racist egalitarian bias of anthropology, the academy in general, and the dominant narrative of Western society as a whole, there is a strong tendency to assert flatly that “race does not exist” as a biological concept. There is no interrogation of the concept of race except to refute its utility. This is not a case of agnostic skepticism washing away illusions, but a case of skepticism applied in a fashion to obtain a clear and distinct objective result which corresponds to reality. When it comes to race many become naive realists who accept that biological concepts can be falsified or verified in a simple and straightforward fashion. There is all of a sudden one Way of Knowing which presents us with indubitable truths.
Here is L. L. Cavalli-Sforza (my question in italics):
7) Question #3 hinted at the powerful social impact your work has had in reshaping how we view the natural history of our species. One of the most contentious issues of the 20th, and no doubt of the unfolding 21st century, is that of race. In 1972 Richard Lewontin offered his famous observation that 85% of the variation across human populations was within populations and 15% was between them. Regardless of whether this level of substructure is of note of not, your own work on migrations, admixtures and waves of advance depicts patterns of demographic and genetic interconnectedness, and so refutes typological conceptions of race. Nevertheless, recently A.W.F. Edwards, a fellow student of R.A. Fisher, has argued that Richard Lewontin’s argument neglects the importance of differences of correlation structure across the genome between populations and focuses on variance only across a single locus. Edwards’ argument about the informativeness of correlation structure, and therefore the statistical salience of between-population differences, was echoed by Richard Dawkins in his most recent book. Considering the social import of the question of interpopulational differences as well as the esoteric nature of the mathematical arguments, what do you believe the “take home” message of this should be for the general public?
Edwards and Lewontin are both right. Lewontin said that the between populations fraction of variance is very small in humans, and this is true, as it should be on the basis of present knowledge from archeology and genetics alike, that the human species is very young. It has in fact been shown later that it is one of the smallest among mammals. Lewontin probably hoped, for political reasons, that it is TRIVIALLY small, and he has never shown to my knowledge any interest for evolutionary trees, at least of humans, so he did not care about their reconstruction. In essence, Edwards has objected that it is NOT trivially small, because it is enough for reconstructing the tree of human evolution, as we did, and he is obviously right.
L. L. Cavalli-Sforza contends that between population genetic variation is not trivially small. This is clear from the fact that one can discern village-to-village genetic distinctions in Europe. Human variation exists, and it is not trivial. It is useful for phylogenetics, significantly impacts salient phenotypes, and, risks for particular diseases. The social construction of race has real biological raw materials. At one end, the transformation of white European converts to Islam through changes in personal appearance into de facto “People of Color” are matters of social construction in totality. In contrast, the blackness of a Dinka from Sudan is a matter of biological categorization. The categorization of Egyptian Arabs with obvious African admixture as “white” in the US Census is a matter of social construction due to bureaucratic contingency, and illustrates the intersection of biological reality and social fluidity. It is well known that when foreign Arabs with obvious black admixture visited the American South there was often a debate as to whether they were subject to segregation, illustrating the tensions between social norms (which would have coded them as black), bureaucratic function (which coded them as non-black usually), and biological reality (where they were an amalgam of a minor black African component with a dominant white Arab component).
Of course it is true that on any given trait variation can span populations. But even in the case given above, of sickle cell, the correlations with ancestry and population are striking. A lower boundary value is that 75% of sickle cell suffers are of mostly African ancestry, despite only 15% of the world’s population being of mostly African ancestry. These statistics refute a platonic model of race, but they do not refute the population-thinking which is at the heart of much of modern biology, pure and applied.
All that said, the word “race” is fraught with a lot of historical baggage. Therefore to study population wide variation you need to focus on “fine-scale population structure” and what not. This trend would be something of interest for cultural anthropologists of science to study. Race is just a word. Even a term as widely accept as species exhibits a fair amount of flexibility on the margins. But the underlying biological patterns, and the instrumental utility of those patterns, can not be denied.
Addendum: I often use “human” or “humankind” where earlier norms would be to use “man” or “mankind.” My main rationale is I don’t want annoying comments objecting to the term. The concept which I’m pointing to is the same no matter the pointer, and so I don’t mind changing it to facilitate my intent to communicate clearly and without undue extraneous baggage.
Rosie Redfield has a “must read” post, Arsenic-associated bacteria (NASA’s claims). I won’t excerpt it, read the whole thing. To me it is very interesting that many pieces of her critique are ones I’ve encountered in emails or Facebook postings. She stitches them together into a coherent whole. She’ll be writing a letter to Science. Hopefully they’ll publish it. Even if you don’t have a deep background in microbiology and biochemistry I think it was clear that the authors had jumped to some inferences too quickly.
(Acknowledgement, John Hawks)
Update: Also, Arsenate-based DNA: a big idea with big holes:
So the Sargasso Sea tells us that some bacteria are capable of making DNA at very low phosphate concentrations. The most plausible explanation is that the bacterium GFAJ-1 can make normal DNA at micromolar phosphate concentrations, and that it also has the ability to tolerate very high arsenate concentrations.
This seems like the “boring,” but most plausible, explanation.
Update II: David Dobbs reviews the journalistic response. I think that people who write about science were in a bind because of the structural problems that David points out. When I first skimmed the paper it seemed to claim too much, but I had to keep in mind that it got through peer review. On the other hand as I stated once scientists in a position to critique on a genuinely technical dimension started complaining really loudly on social networking, that changed my own perception really quickly.
One of the most persistent debates about the process of evolution is whether it exhibits directionality or inevitability. This is not limited to a biological context; Marxist thinkers long promoted a model of long-term social determinism whereby human groups progressed through a sequence of modes of production. Such an assumption is not limited to Marxists. William H. McNeill observes the trend toward greater complexity and robusticity of civilization in The Human Web, while Ray Huang documents the same on a smaller scale in China: A Macrohistory. A superficial familiarity with the dynastic cycles which recurred over the history of Imperial China immediately yields the observation that the interregnums between distinct Mandates of Heaven became progressively less chaotic and lengthy. But set against this larger trend are the small cycles of rise and fall and rise. Consider the complexity and economies of scale of the late Roman Empire, whose crash in material terms is copiously documented in The Fall of Rome: And the End of Civilization. It is arguable that it took nearly eight centuries for European civilization to match the vigor and sophistication of the Roman Empire after its collapse as a unitary entity in the 5th century (though some claim that Europeans did not match Roman civilization until the early modern period, after the Renaissance).
It is natural and unsurprising that the same sort of disputes which have plagued the scholarship of human history are also endemic to a historical science like evolutionary biology. Stephen Jay Gould famously asserted that evolutionary outcomes are highly contingent. Richard Dawkins disagrees. Here is a passage from The Ancestor’s Tale:
…I have long wondered whether the hectoring orthodoxy of contingency might have gone too far. My review of Gould’s Full House (reprinted in A Devil’s Chaplain) defended the popular notion of progress in evolution: not progress towards humanity – Darwin forend! – but progress in directions that are at least predictable enough to justify the word. As I shall argue in a moment, the cumulative build-up of compelx adaptations like eyes strongly suggest a version of progress – especially when coupled in imagination with of the wonderful products of convergent evolution.
Credit: Luke Jostins
One of those wonderful products is the large and complex brains of animals. Large brains are found in a disparate range of taxa. Among the vertebrates both mammals and birds have relatively large brains. Among the invertebrates the octopus, squid and cuttlefish are rather brainy. The figure to the right is from Luke Jostins, and illustrates the loess curve of best fit with a scatter plot of brain size by time for a large number of fossils. The data set is constrained to hominins, humans and their ancestors. As you can see there is a general trend toward increase cranial capacities across all the human populations. Neandertals famously were large-brained, but they exhibited the same secular increase in cranial capacity as African Homo. On the scale of Pleistocene Homo and their brains the idea of the supreme importance of contingency seems ludicrous. Some common factor was driving the encephalization of humans and their near relations over the past two million years. This strikes me as very strange, as the brain is metabolically expensive, and there are plenty of species with barely a brain which are highly successful. H. floresiensis may be a human instance of this truism.
But what about the larger macroevolutionary pattern? Is there a trend toward larger brain sizes in general, of which primates, and humans in particular, are just the most extreme manifestation? Some natural historians have argued that there is such a trend. But, there is a question as to whether increased brain size is simply a function of allometry, the pattern where different body parts and organs tend to correlate together in size, but also shift in ratio with scale. The nature of physics means that very large organisms have to be more robust because their mass increases far faster than their surface area. By taking the aggregate relationship between body size and brain size, and examining the species which deviate above or below the trend line, one can generate an encephalization quotient. Humans, for example, have a brain which is inordinately large for our body size.
And yet there are immediate problems looking at relationships between body and brain size, and inferring expectations. Different species and taxa are not interchangeable in very fundamental ways, and so a summary statistic or trend may obscure many fine-grained details. A new paper in PNAS focuses specifically on various mammalian taxa, corrects for phylogenetics, and also relates encephalization quotient by taxa to the proportion of social animals within each taxon. Encephalization is not a universal macroevolutionary phenomenon in mammals but is associated with sociality:
Evolutionary encephalization, or increasing brain size relative to body size, is assumed to be a general phenomenon in mammals. However, despite extensive evidence for variation in both absolute and relative brain size in extant species, there have been no explicit tests of patterns of brain size change over evolutionary time. Instead, allometric relationships between brain size and body size have been used as a proxy for evolutionary change, despite the validity of this approach being widely questioned. Here we relate brain size to appearance time for 511 fossil and extant mammalian species to test for temporal changes in relative brain size over time. We show that there is wide variation across groups in encephalization slopes across groups and that encephalization is not universal in mammals. We also find that temporal changes in brain size are not associated with allometric relationships between brain and body size. Furthermore, encephalization trends are associated with sociality in extant species. These findings test a major underlying assumption about the pattern and process of mammalian brain evolution and highlight the role sociality may play in driving the evolution of large brains.
A key point is that the authors introduce time as an independent variable, so they are assessing encephalization over the history of the taxon. This is clearly relevant for humans, but may be so for other mammalian lineages. The table and figures below show the encephalization slope generated by using time and body size as the predictors and brain size as the dependent variable. A positive slope means that brain size is increasing over time.
Two major points:
– Note that the slope is sensitive to the level of taxon one is examining. A closer focus tends to show more variance between taxa. So, for example, humans distort the value for primates in general. Bracketing out anthropoids paints a more extreme picture of encephalization, a higher slope. In contrast, the lemurs and their relatives exhibit less encephalization over time.
– The correlation between proportion of species which exhibit sociality and encephalization of the taxon is strong. From the text:
Encephalization slopes were correlated with both the proportion of species with stable groups (order R = 0.92, P = 0.005, n = 6; suborder R = 0.767, P = 0.008, n = 9; Fig. 2 A and B) and the proportion in either facultative or stable social groups (order R = 0.804, P = 0.027, n = 6; suborder R = 0.63, P = 0.04, n = 9).
The last figure makes it is clear that the correlations are high, so the specific values should not be surprising. Don’t believe these specific figures too much, how one arranges the data set or categorizes may have a large effect on the p-value. But the overall relationship seems robust.
A highly encephalized “alien”
What to think of all of this? If you don’t know, one of the authors of the paper, Robin Dunbar, has been arguing for the prime importance of social structure in driving brain evolution among humans for nearly twenty years. The relationship is laid out in his book Grooming, Gossip, and the Evolution of Language. Robin Dunbar is also the originator of the eponymous Dunbar’s number, which argues that real human social groups bound together by interpersonal familiarity have an upper limit of 150-200. He argues that this number arises because of the computational limits of our “wetware,” our neocortex. Those limits presumably being a function of biophysical constraints.
One interesting fact though is that the median cranial capacity of our species seems to have peaked around one hundred thousand years ago. The average human today has a smaller brain than the average human alive during the Last Glacial Maximum! (see this old post from Panda’s Thumb, it’s evident in the charts) This may be simply due to smaller body sizes in general after the Ice Age. Or, it may be due to the possibility that social changes with the rise of agriculture required less brain power.
Ultimately if Dunbar and his colleagues are correct, if social structure is the most powerful variate in explaining differences in brain size when controlling for phylogenetics and body size, then in some ways it is surprising to me. After all, it does not seem that ants have particularly large brains, despite being extremely social and highly successful. Clearly the hymenoptera and other social insects operate on different principles from mammals. Instead of
developing “hive minds,” it seems as if in mammals greater social structure entails greater cognitive structure.
Citation: Susanne Shultz, & Robin Dunbar (2010). Encephalization is not a universal macroevolutionary phenomenon in mammals but is associated with sociality PNAS : 10.1073/pnas.1005246107