Breed and Dotterrer 1916

My actual research has nothing to do with behavior, which could be a bit of a surprise given that all I've written about on here (so far) is my reaction to a popular science book about human behavior. In reality, I study the process of evolution itself, and I do so using bacteria. Bacteria offer a number of useful advantages in studying evolution: rapid generations, easy to manipulate environmental conditions, large population sizes, few ethical problems (things without neurons can't really suffer the same way tings with brains can), and the ability to freeze the population and revive it later.

With the sort of work I do, one thing I frequently need to measure is how many bacteria of a given type I have in a particular flask at a particular time. Population sizes, as I've said, tend to be very large in bacteria -- the populations I work with are typically around 3 * 10^8 cells -- and it's not really reasonable to count them all. It would also sometimes make the experiment useless, because the cells I take out to count aren't then still in the flask doing whatever it is I want to measure them doing. Instead, what I want is to use a small fraction of the population to estimate what the full population is like. I want a random sample from that population, which is pretty easy because I grow things in liquid culture and my cells aren't capable of making biofilms, so I just need to use a vortexer and make sure the liquid's mixed. Then I need to work with just a small amount of this liquid, and somehow get a reliable count of the number of cells in it.

So far, I've used the word reliable. This is because I'm a bit careful about terminology, and in science, accurate and precise have defined meanings. Ideally, I want my count to be both accurate and precise. Accurate refers to the sample number being close to the real number. Precise refers to multiple different measurements being close to each other. I made my own version of this common figure to demonstrate that, since I couldn't find one that I was sure was free to use (also, so I could ensure it was readable under different color vision impairments):

(Feel free to use this image if it's not for commercial purposes, but if you're going to just copy it I'd appreciate you attaching my name: Mike Wiser)

If the goal is to hit the center of the target, the two images on the top are accurate: if you take the average of all the shots, it will be close to the center. The two images on the left are precise: there is little scatter from one shot to the next. The lower right is neither accurate nor precise; there is a lot of scatter between the shots, and the average of all of them isn't very close to the center of the target. Scientifically, it's fairly easy to test for precision, but it's harder to know much about accuracy in a measurement.

This brings me to the paper I wanted to bring up. When I take my sample of liquid, I then dilute it and spread some of the dilution on an agar plate. Agar is basically science gelatin -- it makes the growth medium thicken and become a semisolid, rather than sloshing around as a liquid. I aim to get a dilution that has a high enough population size that I don't have so few colonies that the variation from one plate to another is larger. But I also don't want to have too many colonies per plate, since colonies can grow into each other (reducing accuracy) and because really dense plates take longer to count (and my own reliability may go down as a function of fatigue). It's long been the lore in the labs I've worked in that you should aim for between 30 and 300 colonies on a plate for reliability; whether that is accurate or precise or both is another matter. That range gives plates such as:

(Apologies to those with color vision limitations -- my work involves me counting the red colonies, and counting the pink colonies, and I realize the distinctions are not terribly visible in certain forms of color vision limitation. As above, if you'd like to use this image and it's not for commercial purposes, feel free so long as you credit my name to it: Mike Wiser)

That seems like a reasonable number of colonies on the plate. But where did this lore come from? A recent conversation I had with a labmate (Alita Burmeister) brought up that she had heard from one of the professors (formerly) down the hall from us that this came from an old study from the dairy industry. With the professor's (Tom Schmidt, now at the University of Michigan) help -- both his, and one of his collaborators (Clive Waldron), I found the paper I was looking for: Breed, Robert S and W. D. Dotterrer. The Number of Colonies Allowable on Satisfactory Agar Plates. J Bacteriol. 1916, 1(3):321-331. (full paper here) In it, the authors spread various dilutions of milk on agar plates, and counted three plates for each dilution to look for ranges in which each of the three counted plates was no more than 20% different from the average. Plates were counted after both 5 and 7 days. As expected, there is an intermediate range of colonies per plate that results in fewer discrepancies between plates than are found in plates with either too few or too many colonies. What exactly this rate of discrepancy is changes from 5 to 7 days, but the general finding is robust. To quote the authors, "Plates having less than 30 colonies or more than 400 colonies show very large percentages of discrepancies." Further, the type of discrepancy changes; plates with an average of 50 or fewer colonies tend to have discrepancies from one or more plates having more than 20% more than the average, while plates with an average of 200 or more colonies have discrepancies from one or more plates have more than 20% fewer colonies than the average.

I think it can be interesting at times to track down these old bits of lore to see who actually did an experiment or made an observation that became a standard part of normal practice within a lab.

Sex at Dawn, part 3

This covers part 3 of the book Sex at Dawn: The Prehistoric Origins of Modern Sexuality. (You can see my reaction to part 1 here. and my reaction to part 2 here.) There are 4 chapters in this section.

Chapter 11: The Wealth of Nature: (Poor?)

This chapter largely covers errors in the thinking of Thomas Malthus and Thomas Hobbes. Malthus used the growth rate of Europeans in the Americas from 1650-1800 to calculate that human population would double every 25 years. This is not a growth rate that humanity has experienced for the majority of its existence -- were it the case that human population doubled every 25 years at all times in history, and world population was roughly 1 billion in 1800 (Wikipedia, for good or ill, posits 1 billion as human population in 1804), that would work out to fewer than 1 person in 1050. Doing the same calculation from today's 7 billion in 2013 would result in fewer than 1 person in 1188. [I ran these calculations; they're not directly in the chapter.] Obviously, those numbers are wrong, so something's up with the growth rate. Instead, they cite sources that the global human population went from about 10,000 protohumans to about 4,000,000 modern humans over 2 million years of being hunter gatherers. Similarly, they attributed Hobbes' view of human nature to his historical context of warfare and religious persecution in England, and in Europe more generally.

They then make the argument that global populations were low, and therefore resources were not scarce. The argue ovulation in hunter gatherers doesn't start until late teens, children are breastfed for 5-6 years at a time, and conception is rare during breastfeeding. All are largely true, though that last point is actually dependent on overall nutritional status of the mother -- family planning based on breastfeeding is hardly foolproof (which I say as a younger child born more rapidly than planned on based on such assumptions: I am a year and 4 days younger than my breastfed brother; you do the math). Still, let's take those numbers at face value. Assuming ovulation beginning at 18, menopause in mid to late 30s, 6 year intervals on birth, that would be a child at ages 18, 24, 30, 36, so likely 4 or 5 child per woman. Assuming some premature deaths and the occasional sterile individual, let's say that means 3 surviving children per woman. That is still enough for a 50% population increase every generation, which is around 27 years. Changing the calculation to a 50% growth every 27 years, the 1 billion people in 1800 would get down to approximately 1 in 882. These factors alone cannot possibly explain how low the human population growth rate was. As the authors argue that humans were spreading into an open ecological niche (and thus weren't locked into a struggle against one another for scarce resources), something else must have been going on.

Basic biology argues that a population expanding into an open ecological niche will rapidly expand in population. The reasons why a population would not be expanding in size are largely limited to:
1: There is a high death rate (predation, disease, challenging physical environment, etc)
2: They have already reached carrying capacity of the system (and thus aren't expanding into an open niche)

The authors then go on to recount stories of a) a few specific communities of an Italian region and their descendents in the new world who were remarkably egalitarian and showed low rates of heart disease, and b) individuals from Tierra del Fuego who had been brought to England to be "civilized", then returned to their homeland and giving up the trapping of Western civilization to return to the normal way of life of their people.

Overall, this chapter's numbers do not make sense, and don't really do much to bolster arguments about what prehistorical human sexual practices were like. There are also repeated assertions that ancestral humans were fundamentally nomadic, but there isn't evidence provided to back this up.

Chapter 12: The Selfish Meme (Nasty?)

This chapter starts with a discussion of the Prisoner's Dilemma. For those unfamiliar with it, it's a basic starting point of a lot of game theory. Imagine that you and another person are brought in by the police for questioning. They tell you that they have some evidence of the two of you committing a crime, but can't *quite* prove the top count. If you rat out the other guy, he'll go to jail for 10 years, while you walk free. If you both stay silent, you'll be convicted of lesser charges and go to jail for 6 months. And if you both talk, you'll both end up in jail for 5 years. They're offering the other guy the same deal. What do you do?

If you're playing the game just once, the correct answer is to rat the other guy out. Why? Well, let's say you have no idea what your partner will do. If he keeps quiet, if you rat him out you go free; if you keep quiet, you go to jail for 6 months. Ratting him out looks better. If he rats you out, if you keep quiet you go to jail for 10 years; if you rat him out, you go to jail for 5 years. Again, ratting him out is the better deal. No matter what he does.

As expected, when you experiment with people and offer them this sort of situation, most people pick to rat the other guy out. The authors then discuss some of the work of Robert Axelrod, showing that if people play the game repeatedly, they start cooperating a lot more often, as they don't want to develop the reputation of ratting the other guy out. This is because they are no longer playing Prisoner's Dilemma -- they are playing Iterated Prisoner's Dilemma, which is a different game. Now they aren't looking for the one-off reward, they're looking to maximize their long-term payoff, and people who can get into long strings of cooperation do better. There is extensive mathematical literature on this in both evolutionary biology and economics. Memory, the ability to select one's partner, and spatial structure are all widely-recognized ways to promote the evolution of cooperation in an Iterated Prisoner's Dilemma.

They then go on to discuss the problems of the thought behind the Tragedy of the Commons. This is another frequent concept in evolutionary biology, this one derived largely from a 1968 paper by Garett Hardin. The idea is that when you have private ownership of some resource (for example, cattle herds) which consume a public resources (in this case, grazing in the common areas), then it will be in each individual's best interest to over-exploit the common resource since the pain of lowered production is shared by everyone, while they reap the profits of their extra cattle. In essence, the pie is getting smaller, but they're getting a larger fraction of it and thus still coming out ahead. Therefore, public resources need some sort of policing mechanism or else the whole system crashes.

As the authors point out, the actual commons being discussed do have policing mechanisms. This doesn't invalidate the general point of tragedy of the commons, it just limits what commons it refers to. Several of the items they list -- open seas, skies, rivers -- are seen as the relevant commons in much of the theoretical discussion of tragedy of the commons these days.

The authors then tie in the work of Robin Dunbar, who argues that with groups larger than about 150 people, individuals do not all know each other and each other's relationships within the group, and social cohesion breaks down. I've always been a bit skeptical of the notions of Dunbar's number as a tipping point, but that's merely a personal reaction and not a fleshed out scientific response.

The chapter then goes on to discuss possible evidence of the detrimental effect of agriculture on humans -- increase in chronic malnutrition, vitamin and mineral deficiency, increased time spent working for food (based on time usage of modern groups, which they assume is the same as was true for ancestral groups -- an assumption I continue to have problems with), and the small sizes of medieval European armor equating with short people. I do know from my college history classes that there is widespread belief among historians that the preserved armor from medieval Europe was the armor made for display, not use, and thus wasn't crafted at full size, but these authors do cite evidence of pre-agriculture peoples in Greece and Turkey being slightly taller than modern residents of those countries.

After this, the chapter goes on to discuss some potential evidence of the benefits of more relaxed ways. Work by Frans de Waal and Denise Johanowizc on two species of macaques -- one typically aggressive, and one far less so -- where they showed that by housing them together they could shift the more aggressive species markedly less so gives a distant primate example that aggressiveness can be socially modulated. And work by Robert Sapolsky (disclaimer: I had a friend who worked in his lab while we were both in the grad program at Stanford) on a field cite of baboons showed that a fluke event which killed off the majority of the aggressive males in the study population but left the others alone resulted in long-term decreases in aggression in this population, even so long after that virtually all of the males in the current population immigrated from other ones.

I find this chapter to either involve a misleading oversimplification of some basic points of game theory, or else to show a misunderstanding of those points. It continues to insist that hunter-gatherers would have had low stress, high leisure societies, but I don't think they've actually demonstrated this about ancestral human groups.

Chapter 13: The Never-Ending Battle over Prehistoric War (Brutish?)

This chapter starts with a criticism of a TED talk by Steven Pinker, in which Pinker discusses percentage of male deaths due to warfare in various societies, all of which are higher than the US and Europe in the 20th century. Most of these other societies are at least partially horticultural societies, which grow substantial crops, and this I feel is a worthwhile criticism of them representing hunter-gatherer societies. I am less convinced of the relevance of the objection that they aren't completely nomadic, as I don't think the authors have actually established that ancestral humans were entirely nomadic.

Next, the authors turn to the lack of bonobos in the discussion of the deep history of warfare and rape among our ape ancestors. While I feel this is somewhat justified in the discussion of warfare -- as warfare discussions among non-humans are typically limited to just chimpanzees, and there's no compelling reason to think our ancestors were more like chimpanzees than like bonobos (and, conversely, no compelling reason to assume the opposite either) -- I feel it isn't particularly compelling in the case of bonobos, as the discussion of rape among apes does include gorillas and orangutans. From a phylogenetic context, it's more likely that something seen among all apes other than bonobos is something the bonobo lineage has stopped doing since separating from the chimp lineage, rather than that the lineage to humans-chimps-bonobos stopped doing and which the lineages leading to chimps and leading to humans both later reacquired.

The book then goes on to discuss the work of Margaret Powers, who called into question some of the findings of Jane Goodall on the chimpanzees at Gombe. Notably, Powers argues that the increased aggression observed at Gombe after the first few years of the study could be laid at the feet of the researchers provisioning the chimps with hundreds of ripe bananas each day during a limited window of time each day. That creation of a highly valuable, physically and temporally restricted resource gave the chimps something to fight over, and may have led directly to the aggression observed. This is a valid point. Unfortunately, they then take this too far in their attempts to apply it to humans, such as their statement that "women and men would have been free to move among different bands in the fission-fusion social system typical of hunter-gatherers, chimps, and bonobos." (p. 191). Maybe. But immigrants in all of these groups end up at the bottom of the social hierarchy (and in both chimps and bonobos, immigrants of only a single sex are typically accepted), and social status has substantial effects of reproductive success.

The authors then go on to discuss how increasing population density appears to be strongly linked to increasing aggression. This seems logical to me. But why would a switch to agriculture automatically lead to higher population density? The authors have argued extensively that foraging resulted in better health, and less malnutrition, than in agricultural societies. If population growth was extremely slow in foraging groups, and agricultural groups had worse health outcomes, how would they have had substantially higher population sizes?

The authors then effectively point out the problems with Napoleon Chagnon's study of the Yanomami people. This take down is well sourced and logically compelling.

It seems to me that many of the points of this chapter are predicated on the assumption that ancestral foragers were inherently nomadic, which I continue to have problems with since I don't feel the authors have documented evidence that this was the case.

Chapter 14: The Longevity Lie (Short?)

This chapter starts out with a reasonable description of how the mean doesn't always give you a useful number about something. Specifically, life expectancy at birth won't tell you much about typical life span if there is high infant mortality -- the mean will be a lot lower than what is typical for people who make it to adulthood. This is completely true. They go on to state that a lot of infant mortality once attributed to starvation and disease probably resulted from infanticide. No citation provided on this in ancestral groups, but rates of 20-50% are reported for several modern forager societies. That is extremely high. Infanticide rates of 50% would have been enough to keep foragers from rapidly filling an open ecological niche, but that would argue that the switch to agriculture isn't what led to the problems associated with population density and resource scarcity, but instead that these are due to a reduction in the voluntary killing of infants. That paints the whole thing in a rather different light.

The authors then go on to talk about how many deadly human diseases come from domesticated animals. This is definitely true in general, though I do disagree with one of their claimed ones: malaria. Given that almost all malarial cases are caused by infected mosquitoes biting humans, and that mosquitoes pick up the infectious agent from many different reservoir sources, I don't think this can be laid at the feet of animal domestication in the way that measles, tuberculosis, smallpox and the like can. It's also clearly not going to apply to all the types of diseases that have plagued humanity. Cholera, for example, becomes more common at higher human population densities, but the causative agents can also live quite well in the environment, and drinking water that has the relevant bacteria in it can cause an initial infection.

There follows a discussion of stress, which the work of Robert Sapolsky, among others, has shown to be quite damaging to health. I have no quibbles with this. I don't, however, feel that they have shown conclusively that chronic stress was lower in prehistoric foraging societies than in agricultural societies, so I'm not confident of the conclusions they draw based on that assertion.

The authors conclude this section with an argument that appeals to the past as terrible and the present as markedly better are inherently conservative, as they deflect criticism away from any current organization of society. They assert that a dispassionate review of the evidence shows that the tens of thousands of years before agriculture were marked by "robust health, peace between individuals and groups, low levels of chronic stress and high levels of overall satisfaction for most of our ancestors." I would argue that a dispassionate review of their own claims and (lack of) evidence to back them up shows that their arguments are flawed, and that they don't have evidence that actually supports many of their assertions about the prehistoric social environment. I don't feel they've clearly established what the ancestral human social environment was like, and thus claims based on this purported environment are going to be dubious.

Sex at Dawn part 2

This covers part 2 of the book Sex at Dawn: The Prehistoric Origins of Modern Sexuality. (You can see my reaction to part 1 here.) There are 6 chapters in this section.

Chapter 5: Who Lost What in Paradise?

This chapter makes 3 primary arguments:
1) Agriculture is more work than foraging.
2) Humans have more sex than any other animal.
3) Humans are more social than any other animal.

Data is not really provided to back these claims. This is most troubling to me on point 1, and I'm hoping that data is provided on this in future chapters.

On point 2, it is probably not necessary to provide substantial data; the authors mention that only humans and bonobos have sex throughout the entire menstrual cycle, and that chimps and dolphins have been observed engaging in sex for pleasure instead of reproductive purposes. On the other hand, most animals have sex relatively rarely, constrained to times of estrus. While that is largely true, I feel that a discussion of sex for pleasure (as opposed to solely for reproductive purposes) should include information about masturbation and same sex coupling, both of which are widely observed across animals, particularly in captivity or domestication. While there are cases where the actual intent is not clear -- is a mounting being performed for sexual gratification, as a dominance display, both, or neither? -- their omission is odd given the context of asserting that sex outside of these four species is confined to reproductive purposes.

For point 3, I would quibble only with the superlative. Humans are an intensely social species on the whole. I don't think it's obvious that we are the single most social species, however. Many species of the eusocial insect -- ants, bees, termites, and wasps -- live in markedly larger social groups than we do, and with reproduction confined to a much smaller percentage of the individuals in society. A variety of mammals live essentially their entire lives in social groups, from the complex groups of cercopithecine primates (think baboons) and spotted hyena to the cooperatively breeding wolves and naked mole rats to the matrilineal groups of elephants and orcas, to name just a few. European starlings form flocks that can number over a million individuals, and a large number of fish species spend their entire lives in shoals/schools. Humans are clearly social creatures, and even more social than most mammals, but I don't think it's clear that we are the single most social species.

Chapter 6: Who's Your Daddies?

This chapter discusses the notions of partial paternity found in a number of South American hunter gatherer societies, though mentions that they are found elsewhere in the world as well. This is the idea that babies can have more than one genetic father. I get the impression that the authors think that these notions refute what they see as the standard narrative of male sexual jealousy. I disagree. As I stated in my first post about this book, evolution of behavior doesn't require consciousness of the genetic impacts of this behavior. In societies in which sharing of material resources in mandatory and largely equal, the notions of cuckoldry do not apply as they do in socially monogamous societies/species in which adult investment in the young is directed toward just specific individuals known or assumed to be kin. The largest cost to males in the latter type of social organization is when they invest heavily in offspring to which they are genetically related, and thus there would be an evolutionary pressure to either increase likelihood of relatedness (through, for example, mate guarding), or to decrease investment in specific offspring and increase the number of sexual partners. Communal groups would seem to be following the last of these listed strategies. That doesn't change the fact that sexual jealousy is expected in societies where children are not invested in communally.

It is asserted again that foraging bands in our evolutionary past likely had multiple overlapping sexual relationships throughout the band, and that these relationships were likely required for the level of social equilibrium and communal standards needed for survival. Again, no evidence is presented, this is merely an asserted position.

This is a small point, but one that has irritated me so far in this book: the authors keep talking about gibbons as if they're a single species. They're not. There are more species of gibbons than there are all other apes combined. So when they say things such as "the three most closely related apes: chimps, bonobos, and their conflicted human cousins" (p. 97), they're wrong -- the species within the Nomascus genus in gibbons are more closely related to each other than chimps and bonobos are to each other.

Not quite as small of a point is their tendency to assume that anything shared between humans and bonobos, but which differs from chimps and gorillas, represents the ancestral state of humanity. As I noted before, it is equally parsimonious to get two independent beginnings of something as it is to get one beginning and one loss. We can potentially distinguish between these two options on likelihood grounds, but we're not going to get there on parsimony alone.

A final point at the end of the chapter is that they state that if one views sex as a way to build and maintain mutually beneficial relationships, non reproductive sex makes a lot more sense, and that things like homosexuality become a lot less confusing. From an evolutionary standpoint, same-sex sexual interactions are no more confusing than masturbation is: individuals who enjoyed sex were more likely to leave descendents, leading to sex in general being enjoyable, leading to individuals finding ways to tap into that enjoyment. What is confusing is exclusive homosexuality -- individuals who only have sex with others of the same sex, because, by nature, that doesn't result in passing one copies of one's genes. Group cohesiveness doesn't address that issue at all.

Chapter 7: Mommies Dearest/

This chapter is a bit unfocused. It starts out with retelling a few anecdotes about how some societies embrace not only the idea of multiple paternity, but also multiple maternity, which any woman who nurses a child is seen as one of that child's mothers. This then segues into anecdotes of societies in which children are raised communally, with all adults being viewed as father and mother. From there, it goes on to discuss the decline of the nuclear family structure within Western societies, and how if the nuclear family were the natural unit in humanity it wouldn't need laws to back it up.

The problem is that these arguments are not well-constructed. The authors state "One wonders, in fact, why marriage is a legal issue at all -- apart from its relevance to immigration and property law." (p. 110), and then in the very next paragraph cite the decline of the percentage of legally married households and the concomitant rise of unmarried couples living together over the past 4 decades in the US as evidence of people not living as nuclear triads (mother, father, children). That isn't evidence for their argument at all -- it's evidence of a) a declining rate of marriage, and b) an increasing age at first marriage. Logical flaws such as this make this chapter underwhelming.

Chapter 8: Making a Mess of Marriage, Mating, and Monogamy/

The point of this chapter appears to be to show that the word marriage means many different things to many different societies. Specific examples are discussed, from temporary arrangements and no fault divorces to permanent bondings which don't require sexual fidelity. I have no issues with this chapter; it is manifestly true that what we call "marriage" differs across societies, and even over time within a given society.

Chapter 9: Paternity Certainty: The Crumbling Cornerstone of the Standard Narrative

This chapter largely has two points:
1) Patriarchy is not universal among human societies.
2) Many species formerly believed to be monogamous are not exclusively so.

Both of these points are true. However, I feel that the authors -- particularly in regards to point 2 -- are either running into a terminology issue, or are falling afoul of a false dichotomy. From my reading of the behavioral literature (which is far from expansive, as this is not my field of study within evolutionary biology), paternity certainty doesn't actually refer to certainty. That is, it doesn't require 100% knowledge. Instead, it refers to the notion that certain behaviors -- and, in organisms recognized as having cultures, certain culture norms -- increase the likelihood that the offspring of a male's social partner are his genetic offspring as well. These are things that increase the certainty, but that doesn't mean that they raise it to 100%. Most often, this falls under the general category of mate guarding, which in this context is essentially the male being around the female during the time period in which she is fertile and ensuring that other males do not mate with her. It also also refer to physical adaptations, such as the formation of a coital plug that prevents future males from inseminating a female until it dissolves. But unless a female is fertile for only an exceptionally short window, males will not be able to absolutely ensure their own paternity in her offspring, and we humans tend to be horrified when we come across some strategies involved (such as groups of 2 or 3 male bottlenose dolphins forcing a female away from the rest of the pod, denying her sleep until she accepts copulation and/or physically forcing the issue, and keeping her prisoner for up to several weeks -- dolphins aren't the gentle creatures of our childhood lore). While many songbirds previously thought to be monogamous turn out to have an appreciable rate of extra-pair paternity, that rate is still well under 50%. That makes it more probable that a given male is the genetic father of a chick in his nest than that he is not, and thus there is a more positive expected value in reproductive fitness for provisioning the offspring than is true for most solitary species.

In regards to point 1, it is good to note that there are human matriarchies, and thus patriarchy is not universal. I assume most biologists already knew or suspected this. I don't yet see what bearing this has on notions of what is the proper way for humans to orient their societies or individual lives.

Chapter 10: A Beginner's Guide to Coveting Thy Neighbor's Spouse

I like the beginning of this chapter. It points out the shortcomings in many cross cultural surveys of people's attitudes about specific things. Namely, such surveys are very commonly limited to university students, who are in turn a non-random sample of the population due to considerations of age, class, and status. And particularly in regards to questions about relationships, their youth is a likely strike against them being a universal sample -- most have had few relationships at the time they are answering hypothetical questions about how they might react under certain circumstances. The respondents are also nearly all embedded within cultures of private property and individualism, which make them distinct from many modern foraging groups. These are quite valid criticisms.

Where I feel the authors go wrong is assuming that modern foraging groups accurately represent the distant past of humanity. As I've pointed out in my previous post, I take issue with the authors' assertion that modern foraging groups "thoughts and behaviors have not been shaped by the effects of modern life and whose perspectives represent the vast majority of our species' experience?" (p. 144). These modern groups do not exist in a vacuum. The land they inhabit is due in part to the results of past conflicts with other peoples, including agriculturalists. Many have dealt with years, even decades, of missionaries seeking to convert them to specific faith adopted by much of the agriculturalist world.

This chapter also includes one of the most interesting finding they provide a citation for: namely, that both men and women state that they would be more upset by the idea of a sexual relationship between their partner and their sibling than between their partner and a random stranger. The authors take this as a blow against the standard model of sexual jealousy. In my interpretation, it is completely expected that women would be more hurt by the idea of their spouse sleeping with their sister than with a stranger. The standard model presumes that women are more troubled by their spouse forming an emotional attachment to another woman, and thus provisioning her and her offspring. Women are going to, as a rule, know their sisters better than they know strangers, and have at least a likelihood of liking them. As such, it is likely easier to imagine her spouse forming such an emotional bond with her sister than with a stranger. On the other hand, I do view men being more disturbed by their spouses having an affair with the man's brother than with a stranger to be a blow against the standard model. If the fear is based on provisioning an unrelated offspring, a child that is genetically a niece or nephew is a lot less problematic than a child who is a genetic stranger. I think this could provide an interesting avenue of research, such as whether men are more bothered by affairs with their brother than with their friends, who presumably they would know well enough to be able to easily imagine the scenario.

The authors present an appeal to the notion that erotic love need not be exclusive, as many other forms of love are not, and that it does not have to follow a zero sum game expectation. This is true, but it depends on the society in which children exist in many ways. These include both the obvious ones -- such as the discussions throughout this book of societal mechanisms by which various forager societies have mitigated sexual jealousy with ritualistic requirements on extra pair sex -- and the less obvious ones such as enforced provisioning of all children by all adults within a group. Without these societal structures in place, significant reproductive conflict within a sex will exist, as one individual gaining resources will come at the cost of another individual losing them.

There is also, at the end of this chapter, another instance of what I feel is an assumption that a behavior must be conscious in order to count. The authors look at forager societies in which sexual bonds are not exclusive, and conclude that the women in them do not have to barter access to sex for food or protection or investment in their offspring. That is one way of looking at it, and potentially valid. It's not the only one. It is also valid to look at this as an example of paternity confusion, where men do not know which children are related to them genetically and which ones are not so they contribute to all of the offspring in the group. In this view, the women are bartering sexual access for resources, but they are doing so so constantly that they do not recognize it as such. I do not know that this is what is occurring, but I see it as at least as consistent with the evidence presented, and it's starting to feel like an elephant in the room.

Sex at Dawn, part 1

Sex at Dawn: The Prehistoric Origins of Modern Sexuality is a popular science book, aiming to address that many of the common conceptions of human sexuality are incorrect.

Part 1 is 4 chapters long.

Chapter 1: Remember the Yucatan.

This chapter is basically an extended way of saying that culture defines a lot of what you consider normal. As such, it is important to recognize that just because something seems (un)natural doesn't mean that it is, and just because something appears to answer a question doesn't mean that it does.

This is a perfectly reasonable point, and I have no objections to it.

Chapter 2: What Darwin Didn't Know About Sex.

This chapter makes a few general points, though I feel it provides virtually no evidence to back up any of its arguments. There seems to be an implication that evidence in support of these claims will be presented later, but until I finish the book I won't know that for certain.

Central Argument: Assumptions about male sexual aggressiveness and female sexual passivity are wrapped up in the culture of Victorian England, in part because this was the context of Charles Darwin.

Darwin's straight-laced nature in regards to the erotic is discussed at length. So are the contributions of several other thinkers to Darwin's notions; particularly, Thomas Hobbes and Thomas Malthus. Hobbes wrote of "nature, red in tooth and claw", and that the in the natural state human lives were "solitary, poor, nasty, brutish, and short", all of which the authors contend are wrong, but they provide no evidence at this point that any of those statements are incorrect. They also discuss Malthus' argument that populations increase geometrically -- that is, doubling across generations -- while food production increases arithmetically (ie linearly) and thus poverty is intrinsic to nature as an important context for Darwin's thoughts on evolution, but the authors argue that this argument is based on incorrect assumptions about prehistory. At this point in the book, though, they do not state what these incorrect assumptions are.

The authors seek to lay out what they view as the standard argument of sexual selection: sperm are cheap, eggs and child care are expensive, men wish to maximize the number of women they can sexually monopolize, women wish to get investment in their children from one mate while potentially seeking out better genes when they're ovulating, men are sexually aggressive and fear sexual infidelity in women, women are coy and fear emotional/financial infidelity in men. They state that nearly all parts of this story are wrong, but they don't state how, or how they know this.

The authors also make frequent appeals to the idea that hunter-gatherer groups, and thus ancestral humans, were aggressively egalitarian and shared nearly everything, and that this should also be seen to include sexual relationships. This may be correct; I do not know. But I have some problems with the sorts of arguments being used:

1) The fact that some behavior is frequently reported in particular types of groups does not mean that it is actually common within these groups.

Humans lie. We do so for a variety of reasons. Possible examples include: our memories are inaccurate; our actions don't correlate perfectly with our ideals; we find it entertaining to see what we can get others (particularly strangers) to believe about us; the lie is seen as more interesting than the truth. I've seen all of these things happen, and on matters less intimate and taboo than sex. This is one of the reasons I value observation significantly more than self-reporting.

2) Current groups are not the same as our ancestors. As we frequently explain in evolutionary biology, humans didn't evolve from chimpanzees. Rather, humans and chimpanzees both evolved from a common ancestral species. It is unfortunately common for us to refer to "higher" and "lower" organisms, or describe some modern organisms as "primitive", but I think that that can lead to real confusion. There were creatures that looked similar to current turtles 220 million years ago (see Greg Mayer's easy to read account about a 2006 paper on a likely precursor to turtles 260 million years ago), but that doesn't mean that turtles haven't been changing for those 220 million years. Instead, it means that the parts which fossilize look quite similar. Behavior, soft body parts, enzymes, gene regulation, etc. can all change while leaving few fossilized cues. Body parts can also change significantly over time without being reflected as different within the fossil record, particularly if the changes are cyclic -- A gives rise to B which gives rise to C which gives rise to A.

The same applies to human societies. Modern hunter-gatherer groups are not necessarily indicative of what ancestral hunter-gatherer groups were like. They too have been adapting over the past 10,000 years in which agriculture swept the globe. Modern groups could easily be a non-representative sample of ancestral ones. Perhaps the groups which were most successful at the hunter-gatherer lifestyle have been the most likely to retain it, while those who were less successful at it switched to either agriculture or pastoralism. Perhaps hunter-gatherers were forced off of highly arable lands by agricultural groups who were more invested in it, and thus the remaining hunter-gatherer groups have needed to rely more on hunting than ancestral groups would have.

Chapter 3: A Closer Look at the Standard Narrative of Human Sexual Evolution.

This chapter goes somewhat more into depth on what the authors view as the standard narrative in human sexuality. Namely, they suggest that there are 4 basic assumptions:
1) Female libido is relatively weaker than male libido.
2) Male parental investment is relatively high in humans compared to many other species
3) Sexual jealousy is different between the sexes
4) Human females have extended sexual receptivity and concealed ovulation

From my understanding, all 4 of these assumptions are borne out by the data on humans. I could be wrong, but I don't yet have any reason to doubt these assumptions. The authors don't actually directly challenge any of these assumptions in this chapter, and they do mention studies which appear to support them -- such as that when women are ovulating they are more likely to wear perfume and/or jewelry, rate stereotypically macho appearance in men as more attractive, and seek out sex outside of a socially-recognized pair bond than they are at other points in their menstrual cycle. Perhaps in a later chapter they will present evidence contrary to one of these assumptions.

Instead, the authors largely cast aspersions on these assumptions by inflammatory language, such as that if women seek out mates based on their wealth, power, status, or protection, and men seek out mates based on their youth, and physical attractiveness, "Darwin says your mother's a whore." (p 50). I do not find that a useful approach in science. This comes closer to an ad hominem attack than a scientific argument, and logical fallacies are rarely good at establishing a point.

They also make faulty assumptions about absolute requirements on these notions, rather than relative requirements. For example, they note that it is questionable to assume that "In the ancestral environment, a man could know which children were biologically his, which presumes that: he understands that one sex act can lead to a child, and he has 100 percent certainty of his partner's fidelity." (p 54). While it would indeed be questionable to assume these things, they aren't necessary for the argument of relative male parental investment in humans. Evolution of behavior does not require conscious awareness of the roots of or the consequences of a behavior; it requires that the behavior be at least partially heritable and that individuals who engage in the behavior have, on average, more offspring than individuals who do not. There essentially isn't a morally-acceptable way for any individual to ensure exclusive sexual fidelity in a partner, but that's not required. Instead, if there are behaviors a man engages in which reduce the likelihood that he is raising offspring which are not genetically related to him -- and if raising offspring which are not genetically related to him reduces either the quality or quantity of his own genetic offspring -- then those behaviors are expected to be selected for, regardless of whether the individual man is conscious of the genetic effects of those behaviors.

None of this is to say that I think we should always model our behavior on what maximizes our own evolutionary interests. Adoption within humans is a good thing; children are not left to starve if their genetic parents die, and are sometimes removed from abusive/neglectful environments when the conditions are realized, and instead placed with adoptive parents. From my last reading of the relevant literature, adoptive parents are actually statistically better parents than are genetic parents, most likely due to the twin facts that a) they become parents by active choice rather than as a consequence of sex, and b) they typically must demonstrate capability of being parents in order to become adoptive parents. From an evolutionary angle, adoptive parents are likely passing on fewer copies of their own genes than if they focused on producing and rearing genetic offspring. That doesn't mean that they aren't making the right choice in becoming adoptive parents. One of the advantages of consciousness is the ability to make choices which may be contrary to our genetic predispositions.

Chapter 4: The Ape in the Mirror.

This chapter largely places humans within the context of the other apes, helpfully making the point that we are, indeed, apes (something often overlooked in humanity).

First there is a nice drawing of a phylogenetic tree of old world primates, and a verbal description of what it means. According to the book,

"If you picture relative genetic distance from humans geographically, with a mile representing 100,000 years since we last shared a common ancestor, it might look something like this:

Homo sapiens sapiens: New York, New York Chimps and bonobos are practically neighbors, living withing 30 miles of each other in Bridgeport, Connecticut and Yorktown Heights, New York. Both just fifty miles from New York, they are well within commuting distance of humanity.
Gorilla are enjoying cheese-steaks in Philadelphia, Pennsylvania.
Orangutans are in Baltimore, Maryland, doing whatever it is people do in Baltimore.
Gibbons are busily legislating monogamy in Washington, D.C.
Old-world monkeys (baboons, macaques) are down around Roanoke, Virginia." (p 62-63)

This is a nice picture. It's also very misleading. It is technically true because of the specific wording "relative genetic distance from humans". But I find this sort of description of a phylogenetic tree misleading because it gives the impression that, for example, gibbons are closer to orangutans than either are to humans. They're not. The last common ancestor between gibbons on the one hand (and realize that there are multiple species of gibbons), and the great apes (that include both orangutans and humans) on the other lived somewhere around 22 million years ago. The last common ancestor between orangutans and humans, on the other hand, was somewhere around 16 million years ago. That means that the genetic distance between humans and orangutans is somewhere around 32 million years -- 16 million along the path from humans to that ancestor, and 16 million along the path from the ancestor to orangutans. The genetic distance between humans and gibbons is about 44 million years. So far, so good. But the genetic distance between orangutans and gibbons is also 44 million years. This sort of geographic picture of distances only works relative to humans -- the distance between other groups is not preserved, and can easily be warped by the choice of where to place them.

The Machiavellian nature of meat sharing among the chimps at Gombe is discussed, and contrasted with the more egalitarian sharing by chimps at Tai. And it is noted that food shortage and surplus in humans tend to bring out heightened hierarchy within social organizations and greater Machiavellian and violent tendencies. But the authors simply assert, without evidence cited, that most of human prehistory had no food surplus to wn or lose and no home base to defend. I would like to see evidence of this before taking this assertion as true.

The authors take issue with the fact that much of the work about non-human primates stresses aggression. For example, they quote McGrew and Feistner with "Chimpanzees give a special call that alerts others at a distance to the presence of food. As such, this is food sharing of sorts, but it need not be interpreted as charitable. A caller faced with more than enough food will lose nothing by sharing it and may benefit later when another chimpanzee reciprocates." This is a very standard explanation of what is known in behavior/evolutionary biology as reciprocal altruism -- when the cost to an altruist is lower, and the benefit to a recipient is high, individuals may engage in behavior that is slightly costly to the them with the expectation that they will benefit when someone else does so in the future. The authors here take exception to why it is necessary to explain away generosity in nonhumans, instead of simply taking it at face value. My response is that altruism is less commonly observed in nature than selfish behavior is, and thus it is cases of altruism which must be explained.

One scientific fact that I find interesting which is brought up in this chapter is that both humans and bonobos, but not chimpanzees, have a repetitive microsatellite in a gene important in the release of oxytocin, a hormone which has many effects but is most known for its role in emotional bonding. They quote Eric Michael Johnson (original here, but you'll need to set your browser to not automatically redirect since he moved hosting shortly after that post went up) "It is far more parsimonious that chimpanzees lost this repetitive microsatellite than for both humans and bonobos to independently develop the same mutations." Maybe. I dug up the paper being referenced, and I can't conclude that from the original research. The sequences of this genetic region were compared in humans, chimps, and bonobos. There was no outgroup included, such as gorillas or orangutans. If other ape species do not share this repetitive microsatellite, either it appearing in the ancestor of humans-bonobos-chimps and being lost in the branch leading to chimps, or it being independently gained in both the branches leading to humans and to chimps requires 2 fixations on the phylogenetic tree. Further, this is a microsatellite repeat, which are among the most frequent classes of mutations, so the general argument that a gain of a specific mutation is less likely than the loss of it doesn't carry the same weight as it does with other types of mutations.

Thus far, I am not particularly impressed with this book. 78 pages into it, and the conclusion of what the authors label part 1, the book offers very little in the way of evidence. It is long on argument, but short on data, and either commits or comes close to several logical fallacies. Perhaps this section is meant primarily as background of what others have argued in the past, and other sections will provide data to bolster the claims made by these authors.