evolution

All posts tagged evolution

Paleofantasy

Book review: Paleofantasy: What Evolution Really Tells Us about Sex, Diet, and How We Live, by Marlene Zuk

This book refutes some myths about what would happen if we adopted the lifestyle of some imaginary hunter-gather ancestor who some imagine was perfectly adapted to his environment.

I’m a bit disappointed that it isn’t as provocative as the hype around it suggested. It mostly just points out that there’s no single environment that we’re adapted to, plus uncertainty about what our ancestors’ lifestyle was.

She spends a good deal of the book demonstrating what ought to be the well-known fact that we’re still evolving and have partly adapted to an agricultural lifestyle. A more surprising point is that we still have problems stemming from not yet having fully evolved to be land animals rather than fish (e.g. hiccups).

She provides a reference to a study disputing the widely held belief that the transition from hunter-gatherer to farmer made people less healthy.

She cites evidence that humans haven’t evolved much adaptation to specific diets, and do about equally well on a wide variety of diets involving wild foods, so that looking at plant to animal ratios in hunter-gather diets isn’t useful.

Her practical lifestyle advice is mostly consistent with an informed guess about how we can imitate our ancestors’ lifestyle (e.g. eat less processed food), and mainly serves to counteract some of the overconfident claims of the less thoughtful paleo lifestyle promoters.

Book review: The Beginning of Infinity by David Deutsch.

This is an ambitious book centered around the nature of explanation, why it has been an important part of science (misunderstood by many who think of science as merely prediction), and why it is important for the future of the universe.

He provides good insights on jump during the Enlightenment to thinking in universals (e.g. laws of nature that apply to a potentially infinite scope). But he overstates some of its implications. He seems confident that greater-than-human intelligences will view his concept of “universal explainers” as the category that identifies which beings have the rights of people. I find this about as convincing as attempts to find a specific time when a fetus acquires the rights of personhood. I can imagine AIs deciding that humans fail often enough at universalizing their thought to be less than a person, or that they will decide that monkeys are on a trajectory toward the same kind of universality.

He neglects to mention some interesting evidence of the spread of universal thinking – James Flynn’s explanation of the Flynn Effect documents that low IQ cultures don’t use the abstract thought that we sometimes take for granted, and describes IQ increases as an escape from concrete thinking.

Deutsch has a number of interesting complaints about people who attempt science but are confused about the philosophy of science, such as people who imagine that measuring heritability of a trait tells us something important without further inquiry – he notes that being enslaved was heritable in 1860, but that was useless for telling us how to change slavery.

He has interesting explanations for why anthropic arguments, the simulation argument, and the doomsday argument are weaker in a spatially infinite universe. But I was disappointed that he didn’t provide good references for his claim that the universe is infinite – a claim which I gather is controversial and hasn’t gotten as much attention as it deserves.

He sometimes gets carried away with his ambition and seems to forget his rule that explanations should be hard to vary in order to make it hard to fool ourselves.

He focuses on the beauty of flowers in an attempt to convince us that beauty is partially objective. But he doesn’t describe this objective beauty in a way that would make it hard to alter to fit whatever evidence he wants it to fit. I see an obvious alternative explanation for humans finding flowers beautiful – they indicate where fruit will be.

He argues that creativity evolved to help people find better ways of faithfully transmitting knowledge (understanding someone can require creative interpretation of the knowledge that they are imperfectly expressing). That might be true, but I can easily create other explanations that fit the evidence he’s trying to explain, such as that creativity enabled people to make better choices about when to seek a new home.

He imagines that he has a simple way to demonstrate that hunter-gatherer societies could not have lived in a golden age (the lack of growth of their knowledge):

Since static societies cannot exist without effectively extinguishing the growth of knowledge, they cannot allow their members much opportunity to pursue happiness.

But that requires implausible assumptions such as that happiness depends more on the pursuit of knowledge than availability of sex. And it’s not clear that hunter-gatherer societies were stable – they may have been just a few mistakes away from extinction, and accumulating knowledge faster than any previous species had. (I think Deutsch lives in a better society than hunter-gatherers, but it would take a complex argument to show that the average person today does).

But I generally enjoyed his arguments even when I thought they were wrong.

See also the review in the New York Times.

RNA in our food

What you eat can influence your gene expression.

A post titled Eat Your Grains says:

RNA from our food can survive digestion, sneak into our cells, and control our genes

Researchers studied MicroRNAs from rice that affect cholesterol levels in mice. The effect appears harmful, which is a kind of defense against predation I’d expect from something that hasn’t evolved to cooperate with animals. (Grains have probably evolved some traits that help humans, but only where farmers have long been aware of the traits). Oddly, the researchers say “miRNAs may serve as a novel essential nutrient”, but I expect them to be harmful on average, except in fruits (which have evolved to attract animals).

Book review: The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending.

This provocative book describes many recent genetic changes in humans, primarily those resulting from the switch from hunter-gatherer lifestyles to agricultural lifestyles. Large changes in diets and disease are the simplest causes of change, but the book also describes subtler influences that alter human minds as well.

I had believed that large populations rarely evolve very fast due to the time required for a mutation to spread. This is true for mutations which provide negligible selective advantage, but the book shows that it’s plausible that a number of mutations have recently gained a large enough selective advantage that the rate at which they become widespread is only modestly dependent on population size. Also, the book makes a surprising but plausible claim that the larger supply of mutations in large populations can mean large populations evolve faster than small populations.

The book is occasionally not as rigorous as I would like. For instance, the claim that Ashkenazi “must have been exposed to very similar diseases” as their neighbors is false if the diseases were sexually transmitted.

Most of their claims convince me that conventional wisdom underestimates how important human genetic differences compared to cultural differences, but leave plenty of room for doubt about the magnitude of that underestimation.

They provide an interesting counterargument to the claim that differences within human populations are larger than the differences between populations. Their belief that differences between populations are more important seems to rest on little more than gut feelings, but they convince me that the conventional wisdom they’re disputing is poorly thought out.

They convinced me to take more seriously the possibility that some Neanderthal genes have had significant effects on human genes, although I still put the odds on that at less than 50 percent.

Most experts were surprised at the news that human DNA seems to contain less than 25000 genes.
Since then signs have emerged that the rest of the DNA (often called junk DNA is quite active, with about 80% of the DNA being transcribed into RNA even though only 1-2% constitutes protein-coding genes.
There’s a lot of mystery about what, if anything, most of that RNA does, but it’s not all junk. One such RNA molecule, HOTAIR, appears to control expression of some genes. RNA has an ability to fold into shapes that may rival proteins in their diversity, so there’s no good reason to think that creating proteins comes close to describing the set of functions that RNA performs.

Book review: Monkeyluv: And Other Essays on Our Lives as Animals by Robert M. Sapolsky.
This collection of essays starts out by rehashing nature/nurture arguments that ought to be widely understood by now, but then becomes mostly entertaining and occasionally quite informative.
He mentions one interesting study which questions sexual selection arguments put forward by Geoffrey Miller and others about animals selecting mates with better genes. The study shows that female Mallards produce stronger offspring after mating with more attractive males because they invest more resources in those eggs, rather than because of anything that seems connected to the genes provided by the males.
He helps explain the attraction of gambling by describing experiments which show larger dopamine releases due to rewards that are most uncertain (the subject thinks they have a 50% chance of happening) than is released when there’s more certainty (e.g. either a 25% chance or a 75% chance) of the same reward.
One place where I was disappointed was when he described “repressive personalities”, which he made seem quite similar to Aspergers, and made me wonder whether I fit his description. “dislike novelty”? My reaction to novelty is sufficiently context-dependent that any answer is plausible. “prefer structure and predictability”? Yes and usually. “poor at expressing emotions or at reading the nuances of emotions in other people”? That’s me. “can tell you what they’re having for dinner two weeks from Thursday”? I could probably predict 5 days in advance with 50% accuracy, so I’m probably closer than most people. So I Googled and found another description (mentioning the same researcher that Sapolsky mentioned) in the Sciences and find descriptions of “repressive personality” that seem wildly different from me (“a strong personal need for social conformity” and “agreement with statements framed as absolutes, statements loaded with the words never and always”). Who wrote this competing description? Wait, it’s the same Sapolsky! It looks like his current description reuses a small piece of an older article with inadequate thought to whether it’s complete enough.

Book review: Why Humans Cooperate: A Cultural and Evolutionary Explanation by Joseph Henrich, Natalie Henrich.
This book provides a clear and informative summary of the evolutionary theories that explain why people cooperate (but few novel ideas), and some good but unexciting evidence that provides a bit of support for the theories.
One nice point they make is that unconditional altruism discourages cooperation – it’s important to have some sort of reciprocity (possibly indirect) for a society to prevent non-cooperators from outcompeting cooperators.
The one surprising fact uncovered in their field studies is that people are more generous in the Dictator Game than in the Ultimatum Game (games where one player decides how to divide money between himself and another player; in the Ultimatum Game the second player can reject the division, in which case neither gets anything). It appears that the Ultimatum Game encourages people to think in terms of business-like interactions, but in the Dictator Game a noncompetitive mode of thought dominates.

I have long been dissatisfied with the attempts I’ve seen to explain why evolution hasn’t made homosexuality rare.
A new paper in PLoS ONE: Sexually Antagonistic Selection in Human Male Homosexuality presents a model that seems adequate.
The main idea (from this summary) is that

a heightened sexual response to men could make women more likely to pass on their genes, while making men possessing the trait less likely to do so.

The paper notes this evidence to support it:

homosexuals’ mothers are more fecund than mothers of heterosexuals. Further female fecundity asymmetries include a higher fecundity of maternal vs. paternal aunts of homosexuals

This model provides hints about why homosexuality is not rare among other species.
My main reservation is that the model leads me to expect bisexuality to be somewhat more likely than homosexuality.

Book review: The First Word: The Search for the Origins of Language by Christine Kenneally
This book contains a few good ideas, but spends more time than I want discussing the personalities and politics that have been involved in the field.
It presents some good arguments against the “big bang” theory of the origin of human language (which suggests that one mutation may have created syntactic abilities that don’t correspond to anything in other species), mainly by presenting evidence that human language is not a monolithic feature, and that most aspects of it resemble features which can be seen in other species. For example, some of our syntactic ability involves reusing parts of the brain that provide motor control.
I’m uncertain whether the “big bang” theory she argues against is actually believed by any serious scholar, because those who may have advocated it haven’t articulated much of a theory (partly because they think there’s too little evidence to say much about the origin of language).
The most valuable idea I got from the book was the possibility that the development of human language may have been a byproduct of a sophisticated theory of mind. Other apes seem to get less benefit from communications because with only the limited theory of mind that a typical chimp has, there’s little that improved communication by one individual can do to increase cooperation between individuals.