Aging is a Group-Selected Adaptation, by Josh Mitteldorf

Josh Mitteldorf's Aging is a Group-Selected Adaptation places its thesis right in the title. Mitteldorf makes a strong case that aging is under the control of evolutionary pressures, and that the selection pressures for it are based on the benefits to groups, since it's clear there's no evolutionary gain to the individual. The evidence that aging is under evolution's control boils down to a comparison of many lineages that have long lives and have evolutionary cousins that do not. This is straightforward and hard to refute. The question is why.

The book's answer is that lineages that don't limit fecundity overshoot the carrying capacity of whatever environment they inhabit. The consequences are frequent population crashes. The alternative that leads to the possibility of stable populations is some feedback cycle that limits reproduction, combined with some way to ensure that deaths occur at a consistent rate. If the genes are optimized for the longest feasible life, then most deaths will occur in times of stress (resource exhaustion, unusual weather, or other cataclysm). This would lead to a much higher chance of ongoing boom and bust, which is a recipe for inevitable extinction.

There are some great graphs in the book illustrating the huge variety in life histories across many species. This one shows survivorship as a function of mortality and fecundity. When mortality is a horizontal line, survival falls consistently from birth to death. (hydra, hermit crabs, et. al.) Some species show decreasing mortality over their lifespan (desert tortoise, white mangrove, redleaf oak, ...), others only a slight uptick near the end (mute swan, tundra vole, sparrowhawk, ...).

According to Mitteldorf, the outcome of many experiments with artificial life show that one of the most valuable features of a species that has to cohabit with predators and prey is the ability to react to changes in its own population so that they have more progeny when the population density is low, and more individuals die when population density is high. The classical reaction to arguments about group selection says that this requires genes to have some kind of foresight, but the paradigm here is that populations that don't discover a way to reinforce this kind of response to population variation will be much more likely to go through frequent bottlenecks. Each bottleneck is another opportunity to go extinct.

One of the key ideas is that in order to contribute to ecosystem stability, rather than only to individual fitness, the genes must find a mechanism that leads to variation in robustness among the population. If some are slower, some are more susceptible to famine or cold, etc., then when a periodic stressor arises, some of the individuals will die. The alternative, if the genes design for uniform robustness is that all survive except when the stressor is severe, and in that case, nearly all will die. Aging, according to this thesis is a mechanism that causes variation within the population, ensuring a steady rate of death, which evens out rapid rises and falls in population. The population can still expand relatively rapidly when a niche opens up, but when living in a stable location, there are forces mitigating against population swings.

For those thinking about how to extend lifespan, a plausible first reaction to the idea that aging is selected for is to conclude that this means that aging will be harder to defeat. I would argue that the opposite may be true. Mitteldorf makes a good case that many lineages have found ways to allow individuals to live to arbitrarily long ages, so the biological mechanisms can't be infeasible or energetically unaffordable. Evolution's lesson is that we should be aware of the consequences of unlimited population growth, but given the demographic transition affecting most advanced economies, we can reasonably be more worried about the dangers of dropping population levels than of too many people. In any case, the hazards for human populations happen slowly enough that we'd be able to react before populations grow to be dangerous.

Aubrey de Grey wrote a response to Mitteldorf, but it looks like it was to an early version of the argument. (The book is dated 2017, but de Grey's 'response' is from 2015.) It looks to me as if de Grey had the reaction I described just above, and thought it was important to refute Mitteldorf's claims. I don't think de Grey directly addresses the arguments in the book. It seems to me that the argument presented here doesn't rule out the possibility of using de Grey's (SENS) approach to engineering fixes for the causes of aging, and it also provides for the possibility of other approaches that would directly intervene in the body's signaling that encourages aging and early senescence. If it's right, it doesn't reduce the number of possible approaches, it adds to them.

0.3productChris Hibbert

The Vital Question, by Nick Lane

Nick Lane's The Vital Question seeks to explain why all eukaryotes share a large number of traits that are completely absent from all bacteria and other simple organisms. As Lane says in his opening page

All complex life shares an astonishing catalogue of elaborate traits, […]. Why, if all of these traits arose by natural selection, in which each step offers some small advantage, did equivalent traits not arise on other occasions in various bacterial groups?

Life arose around half a billion years after the earth's formation, perhaps 4 billion years ago, but then got stuck at the bacterial level of complexity for more than a billion years, half the age of our planet. […] In stark contrast, all morphologically complex organisms […] descend from that singular ancestor about 1.5—2 billion years ago. This ancestor was recognizably a 'modern' cell, with an exquisite internal structure and unprecedented nanomachines encoded by thousands of new genes that are largely unknown in bacteria. There are no surviving evolutionary intermediates, no 'missing links' to give any indication of how or why these complex traits arose, just an unexplained void between the morphological simplicity of bacteria and the awesome complexity of everything else.

Lane claims that this gap in our understanding should be glaringly obvious, and the scientific community should be struggling mightily to fill it in, but (he says) few are working on it, and fewer are talking about it as an important item on the agenda.

Lane's argument is that the combination of bacteria and archaeon that allowed the formation of eukaryotes happened once, and must have quickly evolved to have mitochondria, cilia, and to rely on sex for reproduction, and that all complex life descended from that single event. One of the surprising things is that eukaryotes didn't replace their ancestors; even though they have enough advantages that all complex life descends from that single event, there are still plenty of opportunities for the ancestral forms. The explanation Lane presents is that there's a delicate balance in the energy economy in bacteria and archaea, which doesn't allow the cells to grow much larger, and puts serious constraints on what kinds of mechanisms can be powered inside the cell. When that single archaeon engulfed a bacteria and turned it into the primal mitochondrion, the energy balance changed, and it became possible to store energy and distribute it around the cell, which made it possible to power more kinds of mechanisms, which led to the explosion in the variety of life and ways of living.

The usual story is that the environment changed (the Great Oxygenation) which enabled more styles of living. But what you'd expect if that was the cause would be a separate explosion from every kind of living creature, while what we really see in the evolutionary record is that when there are events like this (the cambrian explosion, e.g.) they radiate from a single progenitor, which tells us there was a significant discovery in that line that enabled the new directions of evolution.

Lynn Margulis' research shows that the form of modern eukaryotes derives from a series of mergers of adjacent bacteria and archaia. (One of the .sig lines I use refers to this) Lane says that while her results hold up, the mergers all occurred in a single line of descent, and all existant eukaryotes radiated out from the same end point of the serial events. Apparently none of the intermediate forms were good platforms from which to generate new life forms.

There are some simpler organisms (giardia among them) that are like eukaryotes in many ways, but lack mitochondria. They have long been viewed as an intermediate evolutionary point between archaia and eukaryotes, but modern phylogenetics (tracing the descent via gene similarity) shows that they're actually descended from eukaryotes, and merely discarded some of the internal structure because it wasn't needed in the environmental niches they occupied. This buttresses Lane's contention that all plants, animals, algae, fungi and protists share a common ancestor.

The common ancestor stored its DNA in a nucleus with a double membrane. The cell itself has a membrane with pores that were inherited by all the branches of its descendants. All the DNA has telomeres as well as introns which are spliced out using common machinery before proteins are built. The golgi apparatus, the form of the cytoskeleton, mitochondria, lysosomes, peroxisomes, the endoplasmic reticulum and the intra-cellular signaling mechanism are also common.

If you're interested, Lane goes into a lot of detail on his hypothesis on the energetic mechanisms that could have led to the evolution of the mitochondrial pathway starting from deep sea hydrothermal vents, where hydrogen and oxygen are bound in a way that can produce positive energy when the bonds are broken. I mostly understood it as I read it, but I'm going to have trouble doing it justice. Here's a precis of the argument; ATP is the end product, and is both stable and easy to extract energy from. A simple mechanism that can produce ATP has the effect of making many energy consuming processes possible.

Hydrothermal vents at the ocean bottom ("black smokers") are places where constantly renewed magma is in contact with sea water, which results in hot acidic water. Lane picks out nearby "alkaline vents" (also on the ocean bottom, but not where magma is exposed) as the plausible site for metabolism to arise. The alkaline version is rich in dissolved hydrogen, accompanied by "other reduced gases including methane, ammonia and sulphide". The rock is riddled with micropores from micrometers to millimeters in size. The flow of warmed sea water is relatively slow, so there's plenty of time for percolation and reaction. There are eddies in the flow, which allows reactive products to accumulate and concentrate locally. Before the Great Oxygenation, the most common gas in both the atmosphere and the ocean was CO₂. In this environment, CO₂ will react exergonically (releasing energy) with H₂ to form CH₄ (methane), but it needs a catalyst.

Lane considers it a crucial clue that all living cells drive their energy metabolism via proton gradients across thin membranes. To expand that, the claim is that the production of ATP always happens in the presence of cell membranes that separate proton-rich from proton-poor regions of a cell, and require a constant supply of H₂ on the low-density side, and produces ATP on the high-density side. On the low density (alkaline) side, the H₂ donates an electron, which is gobbled up in the production of ATP. Both of these reactions happen spontaneously.

Lane then describes a path via which permeable membranes (which don't benefit from better pumping) could evolve to be more selectively permeable, which would allow better pumping to be a benefit. This change makes it possible for the cell to escape from the natural proton gradient, since it can sustain its own internal gradient. Lane hyphothesizes that once selective permeability arises, archaea and bacteria evolved different membrane pumps (evidenced by the fact that they use steroisomers of glycerol) and split into evolutionarily distinct lines.

I'm not sure I explained that very well, but this felt like the first time I've read an explanation of basic cell metabolism that presented a mechanistic picture of the benefit of ATP (stores energy in an easily-extracted form), how the production of ATP is paid for energetically (proton gradients maintained by membranes and selective pumping), and why these designs are fundamental to the difference between bacteria, archaea, and eukaryotes, and eventually lead to the development of chloroplasts as an alternate energy source. Lane gives an explanation at a similar mechanistic level of what happens during apoptosis (programmed cell death; also conserved across the eukaryotes!)

Lane also argues that anti-oxidant supplements interfere with the apoptosis pathway, and thereby reduce health. He presents this as the currently accepted scientific viewpoint, though it's news to me. I need to do more research here.

I learned a lot of biology from this book, and thoroughly enjoyed it.

0.3productChris Hibbert

The Secret of our Success, by Joseph Henrich

Joseph Henrich's The Secret of Our Success has a fair amount of overlap with Herculano-Houzel's The Human Advantage, which I reviewed in July. Both spend most of their attention on explaining why humans, of all the products of evolution, turned out to be the smartest and hence dominant species on the planet. The Human Advantage focused on what makes the human brain unique, and found some surprising neuronal traits that sets mammals apart from other other animals, and that make primates unique among mammals in their neuronal architecture. Henrich, on the other hand, takes pains to point out that individual humans (even very smart ones) aren't very good at figuring out how to survive in new environments. He uses that evidence to argue that communication and culture make the difference. As individuals, he claims, we aren't much smarter than other primates.

They both agree that cooking was a huge step forward for us, but Henrich takes pains to point out that this only an advantage when we're raised in a cultural group. Unlike practically all other animals, we don't instintively know how to unlock the nutrition in common foodstuffs—without training, it would take a long time (during which you have to be subsisting on something else) to figure out how to prepare most of what we eat.

The book starts out with several stories about lost european explorers becoming stranded, and if they didn't get help from locals, they would starve in the midst of what the locals would consider plenty. In Australia, the Arctic, and Florida, well-funded and trained explorers slowly starved because they couldn't figure out how to find, harvest, or prepare the foods the locals subsisted on, and they either didn't think to ask for help, or they drove away those who tried to help them. In contrast, there are a couple of stories of individual aborigines who are separated from their kin, and do just fine for years, since they grew up gathering and preparing the local bounty. His point is that our strength, as a species, is learning from one another, and picking up on every small increment in survivability.

I've been saying for years (since reading Jared Diamond's Guns, Germs, and Steel) that the thing to realize about the spread of humans and their ability to make use of local flora and fauna is that there were enough people, and people are curious enough that we tried to exploit everything, and we tried to make use of everything available in all conceivable ways. How else to explain the fact that people ate acorns, seal livers, and nardoo. In preparing nardoo, the Australian aborigines grind seeds, leech them with water, mix them with ash during heating, and use mussell shells to serve them. If you miss any step, then like the explorers, you'll die of poisoning or stavation with a full belly.

Along the way, this book has lots of interesting proposals about how culture affects prestige and dominance in ways that make it possible for us to live in larger groups and take advantage of the skills and abilities of more people; how competition for living space between groups leads to cultural differences, and how our ability and drive to share culture and learn from each other leads to increasing communication abilties and common grammar strength across the species. There are interesting tidbits spread throughout.

In talking about how living in larger groups with a larger repertoire of tools and techniques make us more capable without requiring more individual smarts or inventiveness, Henrich gave a list of simple tools that is more interesting than the standard list of 6 simple machines known since antiquity:

wheels, pulleys, springs, screws, projectiles, elastically stored energy (e.g. bows, spring traps), levers, poisons, compressed air (blow guns), rafts, leisters [a barbed spear], and heating (fire and coooking).

Instead of focusing on mechanical advantage as we do with the simple machines, this focuses on shared, reusable knowledge, and shows that there were ideas around to be re-used even in societies that were very primitive by modern standards.

Henrich has a longer more detailed time-line than Herculan-Houzel, and his focuses on evidence about tool use showing accumulation of culture rather than archeological evidence relating to brain size, cooking, and gut size. I enjoyed this book as much as Human Advantage, and it added an interesting, non-conflicting story about the roots of our intelligence. It didn't feel as if it has as much relevance to the question about our place in the universe—once we set out on the path toward communication and shared culture, Henrich didn't mention further roadblocks toward increasing advantage as we exploited the new niche better.

0.3productChris Hibbert

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Chris Hibbert

Suzana Herculano-Houzel's The Human Advantage is a good book with some important insights hidden behind a fairly dry and dense presentation on "how I made these important discoveries." Herculano-Houzel (by her own account) pioneered a technique for determining the number of neurons in brain tissue, and managed (through a fair number of mildly interesting adventures) to bring together samples of many different primate, rodent, and other mammalian brains in order to work out the scaling laws that govern how brains and neuron counts grow with body mass in different tissues across different lineages. She shows a lot of graphs and charts to demonstrate that (with two exceptions) for most mammals, neuron counts scale up with an exponent of .5 with body mass, but in primates, the scaling factor is .8. If neurons have to be added in order to increase intelligence, this means that primates have a huge advantage. In order to get smarter, brains and neuron count have to increase. Larger bodies are necessary in order to sustain a larger brain, and if neuron count or neuron density is the limiting factor in intelligence, then you want to be able to pack more neurons into a denser brain in order not to require an enormous body.

Once Herculano-Houzel has established the basic scaling laws, she delves into the economics of maintaining a sufficiently neuron rich brain. The comparative scaling laws mean that as you look at bigger and bigger species of mammals, the neuron counts increase with the square root of the body mass. As primate species get larger, their neuron count increases much more quickly, which means that for a given body size, a primate is capable of supporting a larger brain than would a mammal. The cross-over point where the two lineages have comparable neuron sizes are with body sizes in the 10 gram range. At any larger size, if you compare a primate with another similar sized mammal, the primate is probably smarter.

There is a separate literature showing the energy requirements for many particular species. Herculano-Houzel used her new numbers on neurons for rodent and primate species to show that there is a direct correlation between the number of neurons and the amount of glucose consumed per minute by the brain. For humans (and others in the Homo lineage, being able to take advantage of the primate scaling laws gives a big boost, but you still have to find a way to ingest sufficient calories to afford the bigger brain.

Humans have two main advantages on this score compared to other primates. Walking on two legs is much more energy efficient than knuckle-walking like other (primarily arboreal) primates or on four legs. This increases the range over which foragers could range, and also freed up hands for gathering and carrying. It's not clear what originally drove bipedalism in the homo line, but it occurs at the same branch point that leads to the massive growth in cranial capacity.

The other big human advantage is cooking. I've seen discussions before that cooking increases the efficiency of digestion, and led to our shorter digestive tract, which allowed us to switch energy resources from digestion to our brains, but Herculano-Houzel points out that even before control of fire, other kinds of preparation (chopping and mashing for example) reduce the energy required for digestion. The anthropological evidence for food preparation goes back much further than the evidence of cooking, and significantly after bipedalism. The earliest evidence of eating meat is swiftly followed by anatomic adaptations to a more efficient diet, which is quickly followed by better tools, and the then bigger brains. Part of the evolutionary adaptation for bigger brains included smaller jaws.

Evidence of tool use and manufacture date back to 3.3 MYA (Million Years Ago). This date was recently pushed back from 2.6 MYA. These tools were simple flint knives. Archaeologists wouldn't count rocks that were used for pounding, since they are impossible to distinguish from unworked rocks. The flint knives would have been useful for cutting up meat, which would make it more digestible, and is necessary in order to survive with smaller jaws. Presumably, eating primitively processed foods had to become habitual before later evolutionary steps that relied on it would have survived in the population. The archaeological evidence gives the following timeline:

1. 4.4 MYA: bipedalism appears
2. 3.3 MYA: earliest tool use
3. 2.5 MYA: eating meat
4. 2.4 MYA: beginning of the reduction in size of the jaw
5. 1.9 MYA: smaller gut is clearly present
6. 1.7 MYA to 300 KYA: The Acheulean hand axe
7. 1.5 MYA-100 KYA: start of the increase in cranial capacity
8. 1 MYA: Clear indications of cooking

Another tantalizing clue is that the taste for cooked food may pre-date adoption of the habit. Herculano-Houzel refers to two studies that show that chimpanzees have a very strong preference for the taste of cooked food over raw. I don't know whether this has been investigated in other lineages, but if so, (even if it's just the body innately being able to detect foods that are provide big efficiency gains) it provides a boost for any lineage that can figure out how to reliably prepare foods--once you start, it would be an easy habit to keep, providing that the right food sources and tools are accessible.

Earlier, I mentioned that there are two exceptions to the laws regulating the number of neurons in primates and in all other mammals. The first is gorillas, which have brains and neuron counts much closer to those of other mammals rather than those expected of a primate. This fact about gorillas has been throwing off the results of previous researchers, who could only measure brain capacity. They concluded that the rules for primates would be the same as for other mammals, and argued that it was humans that were outliers. Once you plot the detailed data from small and medium primates and compare to mammals, it's easy to see a different trend line applies, and that humans fit on the primate line and gorillas do not. The other exception is elephants. (Herculano-Houzel has an entertaining section about her adventures getting elephant brains to analyze.) Elephants have brains whose size follows the standard scaling rule for mammals. They're huge, and they have huge brains. But their neurons are distributed very differently from all other species. 98% of the neurons are in the cerebellum, while the normal number doesn't get much above 80%. So elephants have big brains and a lot of neurons, but this explains why they're not even smarter than us, presuming neurons in the cerebral cortex are the thing that matters most.

Anyway, the later clues about cooking and bipedalism only added to my reaction that this work may provide an improved answer to the Fermi paradox. Herculano-Houzel doesn't appear to have data about the brains of animals beyond mammals, but if all the mammals outside of primates share a common scaling factor, then that's an indication that it's hard to evolve intelligence given the standard energy budget. It takes a special trick (which didn't have an immediate obviously benefit in the small primates in which it evolved) which was only discovered in one previously obscure branch of the mammal family tree to enable the efficient scaling that allows bodies to grow large enough to support brains supporting enough neurons to enable tool use. This enables (with other accidents like bipedalism and prepared food appearing in the same lineage) the feedback cycle that led to our massive growth in intelligence.

I've never been very worried by the argument that says the Fermi paradox indicates that there's a Great Filter, and if we can't figure out what the hard step was in our past, we should expect to encounter a hurdle in our future that has stopped other species from getting to space. The Human Advantage makes me even more sanguine. It's hard to evolve an intelligent species. There are a lot of happy accidents in our past, and the likely number of extra-terrestrial species in our light cone may be smaller than we thought. It would be nice to see more data showing the scaling laws that apply outside the primates (and in the cetaceans, which she didn't give much data about). I'll be surprised if any of them show divergent scaling progression compared to baseline mammals.

Sex at Dawn: Ryan and Jethá

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Chris Hibbert

Christopher Ryan and Cacilda Jethá's Sex at Dawn argues convincingly that monogamy isn't particularly natural for humans. It certainly is one common choice, but many modern people have a lot of trouble sticking to the program despite a lot of exhortation and systemic incentives promoting the practice. Ryan and Jethá marshall evidence from anthropology, evolutionary evidence, comparisons with other primates, and examinations of current practices. Their main argument is that a reasonable definition of "naturally monogamous" would mean that most people pair up with someone from the opposite sex, and aren't tempted to stray. There are a few species that mostly act that way, but looking at the broad range of what humans do, we're not like that. It's an interesting question as to why sociologists, and anthropologists seem to want us to believe that it is natural in the face of all the evidence.

There are several places in the book where the authors don't seem to really understand how evolution works. When talking about male parental investment, they ridicule the notion that maximum reproductive productivity is anyone's goal. It's clear from context that they're misunderstanding a discussion in which individuals are described as acting as if maximizing fecundity is the goal. But the evolutionary reasoning is just that those individuals who produce more offspring end up predominating in subsequent generations, regardless of why they acted that way. But regardless of this, they still make a strong case.

When biologists compare anatomy and mating behavior across species, human genitalia and sexual cycles don't make sense for a species in which couples stick together over the long term and don't cheat on one another. The size of male Genitalia, timing and (lack of) visibility of ovulation, breast prominence, are all unnecessary if the pair bond is unshakeable. They make sense when you assume each individual normally mates with multiple individuals of the opposite sex.

Our close relatives the chimpanzees and bonobos don't restrict themselves to single partners and we look more like humans evolved in an environment where individuals didn't restrict their attention to a single partner. In this kind of environment, evolutionary pressures push toward the large penises (by body weight), external scrotum, long duration of intercourse, and large volume of ejaculate you see in humans. If our ancestors had had reliable access to a partner, they wouldn't have needed these (evolutionarily) expensive features.

Another myth they take on is that of the demure female, uninterested in sex. It certainly occurs, but it's not predominant, either in societies (like ours) that constantly promote the idea or in societies that don't. Ryan and Jethá also make it clear that, evolutionarily speaking, homosexuality is nothing to be ashamed of. Our nearest relatives and many other species engage in the practice, though seldom exclusively. Mainstream society's insistance that each person can be categorized as either heterosexual or homosexual, is just not consistent with our behavior or the evolutionary or anthropological evidence.

Anyway, if you're not sqeamish about these topics, it's a fun, eye-opening read. Not likely to change anyone's behavior, but maybe some people will feel less constrained about their choices. It'll probably also provide grist for some arguments, but that's a fine thing, too.

Deutsch on the Evolution of DNA

I posted this on Google+ on Monday. I'll repost here for anyone who's not following me there. It's from David Deutsch's The Beginning of Infinity on the evolutionary origins of DNA as a universal language. I'll post a complete review when I finish the book, but these paragraphs really caught my attention.

Initially, the genetic code and the mechanism that interpreted it were both evolving along with everything else in the organisms. But there came a moment when the code stopped evolving yet the organisms continued to do so. At that moment the system was coding for nothing more complex than primitive, single celled creatures. Yet virtually all subsequent organisms on Earth, to this day, have not only been based on DNA replicators but have used exactly the same alpahabet of bases, grouped into three-base 'words', with only small variations in the meanings of those 'words'.

That means that, considered as a language for specifying organisms, the genetic code has displayed phenomenal reach. It evolved only to specify organisms with no nervous systems, no ability to move or exert forces, no internal organs and no sense organs, whose lifestyle consisted of little more than synthesizing their own structural constituents and then dividing in two. An yet the same language today specifies the hardware and software for countless multicellular behaviours that had no close analogue in those organisms, such as running and flying and breathing and mating and recognizing predators and prey. It also specifies engineering structures such as wings and teeth, and nanotechnology such as immune systems, and even a brain that is capable of explaining quasars, designing other organisms from scratch, and wondering why it exists.

The Rational Optimist, Matt Ridley

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Chris Hibbert

Matt Ridley's The Rational Optimist is a very well written ode to the value of trade and how it contributes to a rational confidence that things will continue to improve for humanity as they have since we first appeared in the world.

Ridley's previous books have mostly been on evolution (though that includes the evolution of cooperation and virtue). Here he's focusing on how trade enriches us all, and how far back trading goes. He uncovers new evidence for the richness of trading in antiquity. One example is Oetzi, the mummified ice age hunter revealed by a receding glacier in the alps in 1991:

[He] was carrying as much equipment on him as the hikers who found him. He had tools made of copper, flint, bone and six kinds of wood: ash, viburnum, lime, dogwood, yew and birch. He wore clothes made of woven grass, tree bark, sinew and four kinds of leather: bearskin, deer hide, goat hide and calf skin. He carried two species of fungus, one as medicine, and other as part of a tinder kit that included a dozen plants and pyrite for making sparks.

Ridley's point is that Oetzi couldn't have collected, sewn, tanned, woven, smelted and sharpened everything he carried himself. The only way he could have accumulated so much useful equipment was through trade. I'm used to arguments for the early emergence of trade that show that quantities of obsidian or sea shells was found hundreds or thousands of miles from where it would have been regularly collected, but Ridley goes to great lengths to display evidence that trade was pervasive and that early people everywhere relied on it extensively for many items in their daily repertoire. It wasn't just an occasional trade for a high-value item, it was a part of routine life, and part of what people ate, wore, and used for healing, hunting, and food storage.

Ridley also carefully lays out the case for Ricardo's point that trade makes us all richer. Expanding the extent of trade increases the size of the market; with more people in your trading community, you can draw on the efforts of specialists who multiply the overall productivity you can take advantage of. Ridley argues that the increasing returns from trade taught our ancestors the value of trust and led to to more virtuous interactions, and better ethical instincts among our ancestors.

The underlying point of much of this is that increasing communication, increasing interaction leads to more and better ideas as we recombine the ideas in new ways, and this leads to the production of more wealth. Around the time of Malthus, it was still possible to argue that increasing production of wealth just made it possible for populations to increase, and didn't really make anyone better off. But sometime in the last two hundred years that started to change, and the recent demographic transition has made that position completely untenable. But pessimism is still more widely respected, and Ridley wants us to understand that a reasonable understanding of the sweep of history and of our evolutionary origins makes optimism a much better fit with our circumstances. Things have been getting better for hundreds of years, and while we can imaging things that might change that, none of them seems particularly likely.

More people are moving to cities where they are more productive and have fewer children. They live wealthier lives than before, and insist on and can afford a cleaner environment and healthier lifestyle. Government restrictions could prevent progress, or trap people outside the cities, or make it harder for them to buy the lifestyle and environmental values they will want, but the smart money goes with the trends. Ridley thinks that the pressure for progress will be sufficient to move governments out of the way, and that spontaneous order will enable people to get what they want. Technology will enhance our healthspan, and our ability to travel and communicate will continue to grow. We'll spend less time working and more on other things. China and Brazil will lead the way if politics in the West grows too stifling.

The Long Tomorrow, Michael Rose

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Chris Hibbert

Michael Rose's book The Long Tomorrow discusses aging in the context of evolution. The book has something of the feel of a memoir— Rose writes about how he happened into this field, who helped and encouraged him, who was right and wrong, and what he was working on along the way.

Rose has spent most of his career single-mindedly breeding long-lived fruit flies (Drosophilia Melanogaster). This approach to achieving longevity has important implications for understanding the mechanisms of evolution and how they impact lifespan. Because the mechanism itself (selective culling and breeding) isn't applicable to humans, the implications for human longevity are indirect, even though they may turn out to be very important for us.

Rose begins his tale at a symposium he spoke at for the Templeton Fund, where eminent scientists and ethicists spoke against any attempt to pursue human longevity as respectively impossible and immoral. Christian theologians joined that chorus, but were opposed by a Jewish scholar, and by Rose himself, already pursuing longer-lived flies. This serves as a nice backdrop and introduction to the issues which allows him to refer back to the controversy and the parties later when he talks about his own views.

In the mid-70s, when Rose was trying to get started in biology, Crick & Watson's theories had been accepted, but the implications weren't yet clear. Scientists were starting to investigate the molecular mechanisms for all kinds of biological effects, both to see how they interacted with evolution and to find the cellular mechanisms that made life function. Hayflick's proposal on the impact of cell division problems on lifespan was getting publicity, but there were few posited mechanisms based on evolutionary reasoning. The Hayflick limit was an observed and accepted fact, but so far without much theoretical context. Thirty years earlier, J. B. S. Haldane had suggested that Huntington's disease (which waits until carriers of the causative genetic defect are in their 30's or 40's to attack) was a consequence of selection's pressure: genes that debilitate before the carriers reproduce will be weeded out, but diseases that crop up later can survive more easily in the population. Peter Medowar expanded on these ideas, but got the evolutionary causality wrong. George C. Williams straightened out a few clues and pointed out that processes that are helpful in the young, and therefore reinforced by evolutionary pressures, might be costly for mature animals but they wouldn't necessarily be corrected because reaching maturity is so much more important evolutionarily than surviving it. Finally, in 1966, William Hamilton put the pieces together and provided an argument based on evolutionary principles that explained why aging would arise. Once Rose studied the history, it was clear that there was some evolution-based theory, but no significant experimental results validating the evolutionary basis of aging. He thought he'd be able to make a mark on this new field fairly quickly.

Brian Charlesworth was Rose's mentor and supervisor when he started the research. Charlesworth had worked out the math for how much selective pressures should fall as a creature aged. Since selection pressures are strongest on the young, you'd expect to see less weeding out of deleterious mutations that affect the mature and the aged than of those that affect the young. Charlesworth proposed that Rose look for an experimental demonstration of that difference in drosophilia, by showing that the fall in fecundity of female flies followed his formulas. Rose spent more than a year in the laboratory, and counted more than a million eggs before analyzing his results. The results showed that Charlesworth's predictions were wrong.

But Rose had started a parallel experiment about half-way through the first one, based on a paper by J. M. Wattiaux (published in 1968) which showed that offspring of older parents lived longer than those born to younger parents. Wattiaux had been unable to demonstrate what he expected to be environmental causes of the difference, but when Rose read the paper, he realized that age of reproduction was the crucial variable that evolution could select on. If only eggs produced from older parents were allowed to reproduce, then the selective pressure (acting on potential parents) would be towards flies that stayed healthy long enough to meet the delayed date. A year after sharing the results of the first experiment, Rose showed that the new procedure (delaying breeding) produced flies that were already living about 10% longer than under standard fly care.

From that point, Rose (and later his students) studied the interactions between longevity, stress resistance (starvation and desiccation), diet and diet restriction, and body fat and other energy storage. They established a positive correlation between long life and all kinds of stress resistance, and showed that body fat and other energy stored in the flies' bodies increased stress resistance. Diet restriction seems to work because it encourages retention of more energy reserves. But all of these mechanisms (except diet restriction) work over evolutionary time scales. Rose wanted to find treatments that can lengthen the lives of those already alive. So he started to investigate molecular mechanisms to see if we can tell what's different within the cells of those predisposed to longer life when compared to their counterparts.

A later series of experiments demonstrated that the death rate, which increases with age, only actually increases from the start of reproduction to its cessation. What this means is that the death rate is strongly controlled by evolutionary pressures. For any species, evolution acts to reduce the death rate as much as possible before the onset of sexual maturity. After that point, it allows the death rate (from natural causes, primarily) to increase relatively smoothly. Once sexual reproduction ends (or possibly a bit later if individuals are still contributing significantly to the life success of their offspring) evolution stops being able to apply selective pressure. This means that the rate at which individuals die (in deaths per capita per annum) stops increasing. For most populations the rate is pretty high by this mature age, and the number of individuals reaching each later age is small, so it's hard to see that the rate isn't changing. But separate experiments done by Rose, Charlesworth, and Larry Mueller show that manipulating the age of last reproduction in populations of drosophilia directly effects the death rates of the resulting populations in only a few generations.

In humans, Rose says that 95 is the age at which mortality rates stop increasing. From 15 to 90, there is exponentially increasing mortality, but after 95, the rates stop increasing. This has two interesting implications for humans. First, many more people are going to make it to their 90s in coming decades, just because we're living so much more healthily and robustly than we used to. That means that there will be much larger cohorts which will see their mortality rates stop increasing, so we should see gradually rising maximum ages, even if nothing else changes.

The other implication is that mortality rates don't increase to 100%. There is always a chance of surviving another year if you aren't hit by a bus. And if Aubrey de Grey is right, our first step is just to clean up our constitutions so that we keep the mortality profile of a 40-something, and we'll vastly improve life-spans. As Rose says:

Aging is not an infinitely high wall of mortality, rising faster and faster as we get older, until everybody is dead. It is a ramp that takes us from a phase of low childhood mortality to a much later phase of high, but relatively stable, mortality. Postponing, retarding, or otherwise mitigating aging does not require pushing back a wall of death of infinite height. It requires smoothing out a ramp of mortality, and possibly lowering the height of the top of the ramp.

At this point, Rose seems to get serious about the implications of his research for human longevity. At the prodding of New Scientist, in 1984, he wrote a lead article proposing that a major, government-backed program to produce long-lived "methuselah" mice would be valuable. He pushed the idea with potential funders from government and the private sector, but never found anyone willing to actually underwrite the proposal. Rose never mentions Aubrey de Grey's Methuselah Mouse project, which I've talked about before. de Grey found private funders to endow a prize, rather than attempting to organize a single Manhattan project-style (Rose's own description) effort.

Having failed at his own efforts to start a project to find ways to apply his research to humans, Rose continues to be upbeat at the prospects that someone will succeed. He finishes the book by offering lots of advice and suggestions on which scientific paths are likely and unlikely to bear fruit, and what modes of organization are worth trying, particularly by people with different skills than his.

My own postscript involves pointing out that Rose didn't talk about what happened to his fruit flies in the end. He was a co-founder of the company Genescient, which uses modern gene assay techniques to look for nutraceuticals that can reproduce the cellular effects present in the Methuselah flies. Rose's name doesn't appear on Genescient's site, so there appears to have been some sort of split. Genescient has spun out Life Code, which markets Stem Cell 100, a nutraceutical based on this research. I haven't started taking it yet, but I do continue to investigate.

Microcosmos: Lynn Margulis and Dorian Sagan

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Chris Hibbert

Lynn Margulis and Dorion Sagan's Microcosmosis a recapitulation of the history of evolution of microbes and how it affects us. The work that Margulis & Sagan report on also led to an article at Edge.org that produced a quote I've been using as one of my email signatures.

All sensory cells [in all animals] have in common the presence of ... cilia [with a constant] structure. It provides a strong argument for common ancestry. The common ancestor ... was a spirochete bacterium.

The copyright date is 1986. A lot has been learned about evolution and microbes since then. Even so, this book is a good introduction to the subject; it's very readable and has lots of detail that is still accepted. The story starts with the very beginnings of life on earth, and is always connected to its affect on how our biology works now:

As we examine ourselves as products of symbiosis over billions of yeaaar, the supporting evidence of our multimicrobe ancestry becomes overwhelming. Our bodies contain a veritable history of life on Earth. Our cells maintain an environment that is carbon- and hydrogen-rich, like that of the Earth when life began. They live in a medium of water and salts like the composition of the early seas.

The presentation is ordered chronologically, starting with the formation of stars and planets, proceeding through the cooling of the earth and the formation of the first entities that could reproduce reliably, the invention of sex and the alternative means of exchanging genetic information, and the change in composition of Earth's atmosphere to something that supported oxygen breathers and was toxic to their precursors. That takes us through the first 3.5 Billion years of the history of the earth, and all of the evolution of macroscopic life occupies the most recent 500 Million years. The emergence of cells, multi-cellular life, and then plants and animals follows, but the microbes are still around and still affecting both metabolism and evolution.

Margulis & Sagan provide a very readable introduction to modern microbiology and modern thinking about evolution. There are certainly more recent books that cover the details of the modern understanding in more detail, but this is a good overview and doesn't miss much that's important.

Gregory Cochran and Henry Harpending: The 10,000 Year Explosion

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Chris Hibbert

Gregory Cochran and Henry Harpending's The 10,000 Year Explosion talks about how humans have evolved over the period since we've been relatively civilized. They explicitly want to challenge the (sometimes vociferously propounded, but seldom cogently defended) notions that humanity hasn't evolved significantly since homo sapiens emerged, and that there's no significant genetic difference among populations in different places. They open Chapter 1 with quotes from Stephen Jay Gould and Ernst Mayr to demonstrate that they aren't fighting a straw man.

Mostly, this notion seems to be held in order to defend a liberal notion of equality, as if we could only defend equal treatment if we all have equal abilities, endowments, and if none of our observable differences are innate. If this notion isn't supportable, we'll have to be clearer that equal treatment is right for other reasons, and perhaps we'll have to be articulate about what those other reasons are. But that's an argument that Cochran and Harpending leave for someone else.

Cochran and Harpending's argument here is that there are quite a few differences between different modern populations, and that many are clearly genetic in origin. They first go to some pains to show that genetic changes can easily arise in this kind of time period. Particular examples are dogs, which have evolved all their modern variety since separating from wolves only about 15000 years ago, and domesticated plants which have changed enormously since the end of the last ice age 11,500 years ago. There are particular changes in humans that are also clearly of recent origin including skin color, eye color, lactose tolerance, and resistance to various diseases, all of which can be shown to be related to geography and to react to evolutionary pressures on much shorter time scales.

With that as background they make a couple of (they expect) radical arguments, and explain a few things that seemed puzzling before. Their first radical argument is that modern humans probably interbred with Neanderthals in Europe, and that therefore, the populations that left Africa probably got a significant contribution from them. I thought they did a reasonable job of demonstrating opportunity, plausibility, and some indications from recent genetic studies that some variations were introduced in the right time frame to have come from Neanderthals. This argument was presented as if the authors expected people to be "outraged at the charge", but it seemed sensible and plausible to me.

The radical argument that I expected to have trouble with is the claim that there's something genetically different about the Ashkenazi Jews. One of the members of the reading group I attend has been making this point for years, and I've been passively resisting it for just as long. Well, Cochran and Harpending put an end to that, easily and without much fight. They showed that the time-frame isn't extreme, that there were sufficient environmental pressures to push for particular changes, and that there's a reasonable case that the Ashkenazi were genetically isolated for long enough for the hypothesized changes in intelligence and susceptibility to diseases to have arisen. They add in some evidence that the diseases specific to the Ashkenazi are tied to genetic changes in neuron development to hammer home the point that the changes in brain function and disease susceptibility are probably tied together. The fact that we already knew (even if we didn't admit it in discussions of evolution) that Tay-Sachs is specific to Ashkenazi and is of genetic origin helps cement the case that evolution has continued into the modern era.

If there had been any remaining doubt that there are genetic predispositions to varying intelligence by race, this pretty clearly puts them to bed. I still agree with the sentiments Les Earnest expressed in his 1989 article Can Computers Cope with Human Races? It's not clear that there's anything useful to be done with this fact, and it's pretty clear that many people mis-apply the fact, but it's a fact none-the-less.

Explosion makes a fairly strong case that evolutionary stasis doesn't happen without a static environment. Humanity hasn't been static over the last 100,000 years--there have been many changes in our way of life over that period, and the changes keep accruing faster than evolution has been able to catch up. Our bodies are still adapting to changes in diet since the agricultural revolution and continuing changes in the sources of our food. Our susceptibility to disease has varied dramatically across populations, and the differences haven't settled down yet. There are still vast differences in hygiene between first world and developing nations and many places in the world where populations are sparser and provide fertile ground for new diseases to arise or transfer to human hosts. There is less of a case for sufficient continuing genetic isolation to drive differing evolutionary pressures for intelligence, but there is certainly pressure for differing intellectual capabilities than were selected for 200 or 500 years ago, much less 1000 years ago.

We haven't finished adapting to the civilization that surrounds us, and the form of our civilization continues to change. We shouldn't expect continuing evolution to be visible on a human time scale, but we shouldn't be surprised that many of the differences among people can be explained as the effect of different evolutionary pressures on our ancestors. In some cases, like disease susceptibility, we can take advantage of it if we stop treating it as tainted information. In others, as race, we should in most cases pay more attention to the abilities of individuals, rather than to the predispositions predicted by apparent racial categories.

James Flynn: What is Intelligence?

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Chris Hibbert

In his new book, What is Intelligence?, James Flynn tries to explain a few things. First he wants to explain what intelligence is and what its components are, second he wants to explain his new understanding of the Flynn effect, and what it implies about genes and intelligence, and thirdly, he wants to convince us that what The Bell Curve said about intelligence and race isn't supported by these new understandings. He succeeds admirably at the latter two; his success in explaining the nature of intelligence is limited.

For anyone who isn't familiar with the Flynn Effect, I'll repeat the findings briefly. More than two decades ago, Flynn noticed that IQs have been going up over time. About 3-5 points per decade, independent of culture, location, sex and race. The people who write intelligence tests have known for quite a while; they reissue their tests every decade or so, and "re-norm" the results. Since the definition of IQ is that 100 is the average score across the population (which population? That's a separate question; read the book if you want the details) they have to measure the results for a standardized group, and set the scoring so the current test will give the right results.

One of the consequences that matters to Flynn is the implication for death penalty cases, which he has been brought into recently. The implication is that if you give someone a test that is 10 to 15 years out of date, their score will be artificially inflated, since they are being measured by the norms of an earlier period. The obvious argument among defenders of capital cases is that death row inmates should be tested by up-to-date standards so as not to inflate their scores and accidentally rate them as competent to stand trial when they are in fact borderline or below it. Flynn points out that it's common for schools in disadvantaged areas and for prisons to not replace their existing stock of test booklets when a revision is issued, so they can be significantly out-of-date, which artificially inflates the scores and negates one escape route.

Like all good scientific revolutions, Flynn starts with four paradoxes arising from the combined data about rising scores.

• Different sub-tests (e.g. vocabulary, spatial reasoning, abstract analogies, pattern matching) have shown different increases. What's different about the areas in which intelligence is growing the fastest?
• Given the size of the increase, why doesn't it seem clear in everyday interactions that each generation is significantly smarter? 20 years is almost 10 IQ points, so two generations is nearly 20.
• How did our ancestors get by if only 100 years ago, everyone was mentally retarded by current standards?
• The changes are so rapid that they can't be genetic, so they must be due to environmental changes, yet studies comparing twins raised together and apart show that environment makes little difference to adult intelligence. Why does the environment make so much difference in some cases and so little in others?

Flynn's resolution is that the environmental differences that matter are large-scale and societal. He also argues that the societal differences compound, so even though small changes are scattered throughout our schooling, entertainment, child-rearing practices, employment expectations, and hobbies, the effects can be pervasive. The area of change that Flynn pinpoints is reliance on abstraction. This turns out to be a common thread among the sub-tests with the highest increases. Our ancestors dealt with the world much more concretely, and modern child rearing, education and entertainment all exercise our growing competence at abstraction. The results from twin studies are dominated by society-wide practices, and show that which family one is raised in, or which schools one goes to don't matter nearly as much as which era, and which society. An agrarian society that doesn't expect its children to grow up and leave the farm raises them to focus on the here and now. Expectations change when horizons open up, and we should expect every society to undergo a Flynn effect as people expect the next generation to live in cities, work in information-intensive jobs, and socialize with people who aren't all doing the same work their ancestors have done since time immemorial.

Ultimately, Flynn's book provides a satisfying resolution to the problems raised by IQ differences. The implications of Murray and Herrnstein's The Bell Curve for racial differences have been neutralized. Not by ethical arguments or posturing, but by a careful analysis of the data. Murray and Herrnstein were led astray by the surface implications of the data when analyzed within generations. If they hadn't written up their analysis carefully and thoroughly, Flynn wouldn't have been impelled to revisit the data and produce a sounder conclusion. Murray and Herrnstein's conclusions weren't original with them; their contribution was their willingness to explain an unpopular idea carefully enough that its limitations would become visible when the right context became apparent.

Murray and Herrnstein's other conclusions still stand: modern societies do an extremely good job of separating out the (relatively small, we now know) within-generation differences in intelligence, and directing people to different pursuits and occupations. The consequences is a shortage of general problem solvers in areas where intelligence is less valuable, while our institutions evolved in circumstances where general problem solvers were widely distributed.

Edward O. Wilson: On Human Nature

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Chris Hibbert

Edward O. Wilson's On Human Nature is an enjoyable read. (It won a Pulitzer Prize, so this is no surprise.) Even though it was written in 1978, it continues to provide a good overview of much that is still held to be true about human biology and sociology. There are chapters addressing Heridity, Agression, Sex, Altruism, and Religion. Wilson is a gifted writer, and can explain subtle concepts with clarity. The opening chapter posits that we are evolved creatures, and that our brains are effectively machines constructed out of billions of nerve cells that bottom out in chemical and electrical interactions. With this as context, Wilson says that the central dilemmas of our existence are that we have no pre-established goals, and that our development of morality on a scientific basis has been short-circuited by the fact that much of our ethical instincts are inculcated by our heridity and environment. In order to understand how we can have goals beyond those evolution set for us, or understand morality in any depth, we first have to understand the biases that evolution has built into us.

The heart of the book is an exploration of what human nature consists of. Wilson provides clear contrasts with the many other creatures (from insects to higher mammals) that he has studied. He points out the myriad ways that social behavior differs across species, both to show how different thinking creatures might be, and to provide context for an argument that the "natural" drives we have evolved shouldn't be treated as guides to correct behavior. If religion can be systematically analyzed and explained as a product of the brain's evolution, its power as an external source of morality will be gone forever. He follows that with this statement of principals:

The core of scientific materialism is the evolutionary epic. Let me repeat its minimum claims: that the laws of the physical sciences are consistent with those of the biological and social sciences and can be linked in chains of causal explanation; that life and mind have a physical basis; that the world as we know it has evolved from earlier worlds obedient to the same laws; and that the visible universe today is everywhere subject to these materialist explanations.

The one thing I would fault Wilson for is for not addressing his first dilemma more strongly. I think he did a good job of showing that religion and our instincts are not a sufficient basis for establishing goals for us to pursue. But that doesn't leave us adrift in an uncaring cosmos; the first task of any maturing person is to discover or invent their own goals. Morality and ethics provide boundaries on that search, but everyone has to find their own destination. Wilson instead falls back on a shared goal of progress and scientific exploration. I do admire his eloquence. This is how he closes the book:

The true Promethean spirit of science means to liberate man by giving him knowledge and some measure of dominion over the physical environment. But at another level, and in a new age, it also constructs the mythology of scientific materialism, guided by the corrective devices of the scientific method, addressed with precise and deliberately affective appeal to the depest needs of human nature, and kept strong by the blind hopes that the journey on which we are now embarked will be farther and better than the one just completed.

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J. Phillipe Rushton: Race, Evolution, and Behavior

0.2 Chris Hibbert Race, Evolution, and Behavior

J. Phillipe Rushton's Race, Evolution, and Behavior covers a sensitive topic, racial differences, in a lot of detail, and with a heavy hand. Most of the book is overflowing with statistics and citations to an enormous number of references in quite a few fields by quite a few researchers. If the idea was to overwhelm the reader, I'll admit it was successful in my case. I eventually learned that I could skim the statistics, and look for prose summaries of the significance. Rushton didn't pay much attention to what it all means until near the end.

Rushton's main point is that there are several attributes on which there is systematic variation among the races, and his claim is that the consistency hints at a possible cause. He's mostly interested in convincing us of his pet theory of the cause of the differences. He's weighing us down with evidence to show us how consistent the inter-racial differences are. He mentions exceptions to the trends, but doesn't give them much emphasis, or provide plausible explanations within his framework.

The traits that Rushton focuses on include brain size, intelligence (as measured by IQ tests and other tests that correlate with g), maturation rate, personality, social organization, and reproductive effort. Other than intelligence (and brain size which is strongly correlated with it), and arguably social organization, these are not scales with a good end and a bad end, they're just differences. The consistency that Rushton focuses on is that whichever of these attributes you measure, you end up with whites in the middle, and orientals and blacks to either side. The story that Rushton wants to build out of that data is that the differences line up the way you'd expect if you tried to predict the direction from r/K evolutionary theory. (Basically, differential evolution in environments of scarcity and plenty; in this case, evolution in the tropics versus the northern latitudes in the Ice age.) He makes a fairly good case for the consistency; there appears to be something going on that puts orientals and blacks at two extremes and whites somewhere between them. But his favorite explanation doesn't seem to be strongly supported. It's roughly consistent with the data, but I'd need more explanation for the exceptions before I'll accept the case as demonstrated.

My biggest complaint about the book is about an important point, orthogonal to Rushton's argument, that he doesn't address at all. Rushton clearly knows that discussion of racial differences is a hot-button issue, and the reason that people care is not because of the difference the data will make to our beliefs about the evolutionary causes of the difference. It's a hot-button issue because accepting the data seems to tell us something significant about innate differences or tendencies to differ among people on aspects of behavior that matter to social policy. When Murray and Herrenstein addressed these issues in The Bell Curve, they were careful to give us the important caveat: the differences between the mean IQs are significant, but the overlap among the curves is large. That means that you can predict the average IQ of a group if you know the racial make-up, but you don't really know much about an individual from that detail. (Wikipedia has a nice graphic showing how much overlap there is among the curves. With the other attributes Rushton discusses (aggressiveness, impulsivity, law abidingness, life span), it's much harder to figure out what interventions might be called for if we knew the differences were significant and pervasive, but not knowing how much overlap there is between races on these measurements makes it hard for me to even tell whether they matter other than in discussions about evolutionary causes.

Another factor, relating to intelligence, that was brought up at the reading group, is fascinating and was completely unaddressed. Rushton says that American Blacks have an average IQ of 85, while in central Africa, the number is closer to 70. In the US, we have the feeling that we could immediately recognize someone with an IQ of 70 as subnormal, but if that's the average in sub-saharan Africa, then something else is going on, because you have to assume that 90% of the population is functional. So the IQ of 70 must mean something different than what we'd assume here, where it normally implies other deficits than just cognitive. It's not clear what an average IQ of 70 in a functioning population would mean. This casts some doubt in my mind on the usefulness of IQ for cross-cultural or cross-racial comparisons. The Wikipedia article makes similar observations.

As to Rushton's thesis, I remain unconvinced that r/K theory is the best explanation for the differences. r/K theory is well-established from studies of other animals, but Rushton isn't careful in marshalling his arguments to convince me that r/K with appropriate caveats for some unexpected cases provides a good enough match to the data. Wikipedia mentions several attacks on Rushton's thesis and methods, but no alternative explanations of note. That's fine; sometimes the facts you need for the right theory aren't at hand when you want them.

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