Monday, March 27, 2006

Richard Dawkins: Accidental Friend of Intelligent Design?

Does Richard Dawkins really lend succour to intelligent design lobbyists? Only if you listen to the intelligent design advocates.

March has seen the publication of a new 30th-anniversary edition of Richard Dawkins’ classic The Selfish Gene, as well as a Festschrift edited by two former students, Alan Grafen and Mark Ridley (now distinguished evolutionary biologists themselves, though Ridley (not to be confused with Matt Ridley) has perhaps focused more on textbook writing than research). Among all the praise being heaped on Dawkins as this anniversary is celebrated, a few dissenting voices are to be expected. And the Guardian’s Madeleine Bunting has once again stepped up to the task (I responded to a previous column of Bunting’s, in which she trashed Dawkins’ recent two-part documentary The Root Of All Evil? here).

The latest piece is much more reasonable in tone than her previous attack, and makes a point that others have made, and which I expect many more will be sympathetic to: that Dawkins, and other evolutionary thinkers and atheists such as Dan Dennett, do a disservice to the battle against creationism and intelligent design — indeed, the charge is that they undermine the case for teaching evolution in classrooms, and provide support for the claims of religiously motivated groups that want evolution dropped from curricula.

Bunting points out that some intelligent design ‘theorists’ (yes, they’re sneering quotation marks) actually like having Dawkins around, so well does he serve their ends:
William Dembski (one of the leading lights of the US intelligent-design lobby) put it like this in an email to Dawkins: “I know that you personally don't believe in God, but I want to thank you for being such a wonderful foil for theism and for intelligent design more generally. In fact, I regularly tell my colleagues that you and your work are one of God's greatest gifts to the intelligent-design movement. So please, keep at it!”
And it’s not just intelligent design advocates who think that Dawkins and Dennett are bad for the argument for teaching evolution (and therefore good for the intelligent design movement):
Michael Ruse, a prominent Darwinian philosopher (and an agnostic) based in the US, with a string of books on the subject, is exasperated: “Dawkins and Dennett are really dangerous, both at a moral and a legal level.” The nub of Ruse's argument is that Darwinism does not lead ineluctably to atheism, and to claim that it does (as Dawkins does) provides the intelligent-design lobby with a legal loophole: “If Darwinism equals atheism then it can't be taught in US schools because of the constitutional separation of church and state. It gives the creationists a legal case. Dawkins and Dennett are handing these people a major tool.”
A whole bunch of issues are tied up in this one small paragraph (I’ll return to the legal aspect below). First, it’s not clear that Dawkins argues that Darwinism ineluctably leads to atheism, except in perhaps a qualified sense. For Dawkins, one of the best arguments for positing the existence of a creator, or God, is the argument from design: that the natural world provides evidence, through the existence of complex, intricate structures such as eyes and wings, of a designing hand. For Dawkins, natural selection blows this argument out of the water. So if you previously accepted God on the basis of the argument from design, then you can drop that because there’s a much better explanation for the apparent design in nature: natural selection. If this is the case, then you might not have any reason left for asserting the existence of a God. If I don’t believe that something exists, because I have no reason to, am I thereby denying this thing exists, or merely saying that although it could exist I have no reason to believe that it does, so I do not assent to the belief that it does? That is, is this atheism or agnosticism?

Well, logically I think it amounts to agnosticism – but in that case, we’re all agnostic about more things than we could ever enumerate. But if we not aiming for logical certainty (which we can never have about matters of fact, scientific claims included), but merely describing as ‘belief’ those claims we think highly likely to be true, then we might be more entitled to adopt the label of atheist. In this slightly weaker sense of atheism, evolutionary biology might contribute to atheism but does not necessarily lead to it: you could imagine that an inscrutable creator set the universe running, and allowed natural selection to do the heavy lifting of creating the diversity of life of earth (this might make the idea that humans were created in God’s image a bit tricky to sustain). But if this is so, then why are so many evolutionary biologists, and scientists generally (particularly the scientific elite), so often self-proclaimed atheists, in this weaker sense?

Bunting raises a separate point about the creationism/evolution ‘debate’, and responding to this helps, I think, address this question and show why the criticisms of Dawkins and Dennett are misguided:
Across the US, the battle over evolution in science teaching goes on. Just in the past month there have been bills in state legislatures in New York, Mississippi, Nevada and Arkansas promoting intelligent design. Last November the Kansas education board promulgated a new definition of science that allowed for supernatural explanations of natural phenomena. A school district in Kansas rebelled last month, accusing their board of “an utterly false belief that evolutionary science and the scientific method is based on atheistic philosophy. Promoting this false conflict between science and faith erects unnecessary barriers.” At the heart of many of these local controversies is the firmly held belief that Darwinism leads to atheism, indeed that it is atheism. Across the US, a crude and erroneous conflict is being created between science as atheism and religion.
We’ve now switched topics: from a conflict between evolution (and its supposed sequela, atheism) and theism (belief in God), to a conflict between science and theism in general or the claims of specific religions. Now I think there is a much stronger conflict in the second pairing than the first. Here’s why. You can – although I don’t advise it or think that it is necessary – to accommodate both evolutionary biology and religious beliefs (although I do think this requires a double-standard in your epistemology). I’m not entirely sure how people adopt both of these systems of knowledge to their own intellectual satisfaction, but my incredulity is not a strong argument against the possibility of the feat.

However, the conflict between science and religion, in contrast to evolution and theism, seems deeper. I’m not talking about the content of these respective bodies of knowledge, although there is certainly conflict there. I mean that they conflict in a much more fundamental way, in what they deem to be appropriate means of obtaining knowledge about the world, and what counts as a reasonable basis for belief. The empirical methods of science – measuring, collecting, experimenting, analysing – are utterly at odds with religious notions of revelation (through personal experience or scripture), and faith is the antithesis of empirical investigation. It is, for a non-believer like me, very hard to see how you can think that empirical methods are appropriate in the wide range of domains that scientists have applied them — working out the structure of atoms, sequencing genomes, sending people to the moon, unravelling the mysteries of the brain — and yet think faith is a useful or reliable route to knowledge in thinking about something as important as whether there is a creator and moral law-giver running the universe. If you accept faith, why not go the whole hog and abandon evidentiary standards altogether?

This isn’t just a flippant challenge: how do you demarcate between where you use faith, and where you use reason and evidence? Similarly, if you base your beliefs on evidence and rational arguments, you might well find (like I do) no reasons to suggest that God exists. And I think this is why the scientific elite generally tends towards atheism: not because the specific claims of their disciplines are utterly incompatible with a religious conception of the universe (you can always tweak your scientific and religious models to mesh with one another), but because of the approach to knowledge that they follow. Scientific investigation just doesn’t tend towards theism and belief in God, which even believers will acknowledge requires faith. For me, and for Dawkins and Dennett too, the reason evidence and rationality don’t lead to a belief in a God is that there isn’t one there to provide such evidence. But I wouldn’t bother getting into a long argument trying to prove a negative — that the evidence of modern science absolutely rules out any sort of creator. Science just makes such a creator redundant.

So I don’t agree that the conflict between science and religion is erroneous, and the existence of religious scientists doesn’t automatically refute this (I have in mind people such as Kenneth Miller, who robustly defends evolutionary biology against creationism, and yet at the same time is religiously devout). There could be any number of reasons that people, hold scientific and religious beliefs simultaneously: they don’t understand the nature of the epistemological conflict between science and religion; they ignore this conflict so that they can believe in an nice afterlife or a foundation for morality or whatever; and so on.

The legal point Ruse alludes to seems pretty weak. Just as not believing in UFOs doesn’t make me a UFOlogist of any stripe, so not believing in a God or the claims of any specific religion doesn’t make me theistic or religious in any sense. I’m simply not a theist — I’m an a-theist. So omitting God from discussions of how the world came to be is not analogous to the religious, faith-based conviction that you have to bring God into the picture (intelligent design, despite it’s claims to be an empirical ‘science’, is really a sophisticated attempt to sneak God in the back door as a prelude to the complete overturning of naturalistic science). You don’t need to invoke God to explain organic diversity because evolutionary theory does a much better job — so does that mean that it’s atheistic, and merely an alternative religious view? This has to be nonsense. You don’t need to invoke God to explain chemical reactions, or the motion of billiard balls, so are chemistry and physics fundamentally atheistic? Are they mere religious claims that, by Ruse’s logic, could be struck out of science classrooms because they infringe the separation of Church and state? You can see where this would lead: you couldn’t teach anything. The legal case against teaching religion because it's a de facto atheistic discipline, and therefore a religious doctrine just like any other, is very poor.

The problem is that Ruse’s complaint might seem superficially appealing to many people – Bunting included. But it seems more of a scare tactic: “Stop talking about your atheism, which we don’t like (for whatever reasons), and don’t stress the conflict between the scientific approach to gaining knowledge, and the faith-based prescriptions of religion, because we want both to exist in happy harmony”. I can see why people might want such an entente cordiale: it would be ridiculous to dismiss the insights of modern science, yet they want the moral or ‘spiritual’ anchor provided by religious belief (if you grant religious belief these powers, which I don’t). Citing the fact that Dembski likes Dawkins, so he must be bad for science, is no good. The reason Debmski likes Dawkins is that Dawkins is both an evolutionary biologist and an outspoken atheist, and often discusses the two together. Dembski, often addressing already religiously committed folk, can say “See what will happen if you let evolution into your life? You’ll end up a Godless heathen like Dawkins! Resist, resist, resist!”. But this is a cheap rhetorical trick, and Bunting, Ruse and others should not take their lead from Dembski.

Monday, March 13, 2006

The Conditions of Kindness

A recent paper by Michael Gurven in Current Anthropology (1) explores how choices about whether help is given to others depends on how generosity is returned.

Asking a favour from a mafia don is not without its costs. It might get you out of a tight spot, or enable you to avenge an enemy, but it comes with burdensome strings attached. The time will eventually come when you are called on to return the favour, and you had better not think about reneging on your obligation.

Even among friends, the returning of favours, or reciprocity, looms large. Most people most of the time, of course, do favours for friends and are not motivated by the prospect of a profitable return on the altruistic investment – it simply feels good to help people we like. But when the flow of favours is unidirectional, we normally notice, and it doesn’t feel good. We feel taken advantage of, which prompts feelings of resentment and, taken to the extreme, can cause the breakdown of friendships.

In the early 1970s, Robert Trivers developed the idea of reciprocal altruism (2) to explain some of the puzzles of animal and human cooperation. The basic idea is simple: you scratch my back, and I’ll scratch yours. Lets say I have a surplus of food today, and you’re going hungry. It hurts me less to give you something to eat than it benefits you (that is, although it might cost me 5 ‘health points’ to lose this food, you might get 10 points by receiving it, particularly if I’m relatively stated and you’re desperately hungry). Fast-forward to a time when the tables are turned, and I’m hungry and your larder is full: if you help me out, we’re square, and we’re both better off than we would have been if we had never helped each other (because we gained more benefit by being helped when we needed it than we lost out when we helped). In this way, a self-serving Darwinian creature can profit from entering into cooperative actions, provided it can discriminate cooperators from non-reciprocators.

The most famous (though not necessarily the best) strategy for getting reciprocal altruism off the ground is Tit-For-Tat (TFT). In this strategy, you cooperate on the first encounter with someone, and then do whatever he or she did on the previous round. So if they did not cooperate on the first move, you withold help on the next round. Likewise, if your partner cooperates, you cooperate on the subsequent move. Although TFT does well in reaping the benefits of cooperation, and of withholding help in some circumstances, it can be beaten by a range of other strategies. TFT, and reciprocal altruism in general, have limitations in explaining the long-term nature of human social interactions, and other routes to the evolution of cooperation are no doubt key to explaining human altruism.

In reciprocal altruism, the benefits of cooperation flow directly back to helpers from those they have helped before. But this needn’t be the case. Benefits can flow back to altruists can just as plausibly through indirect routes: A helps B, B helps C, and C helps A (3). If a reputation for being a good collaborator means that you get more opportunities to participate in profitable cooperative ventures, even if this is with individuals that only know of your character indirectly (through hearing of your reputation), then cooperation can pay, even in a selfish world. Such systems of indirect reciprocity are pervasive in human societies, and have even been proposed to constitute the core of moral systems (4).

A crucial feature of systems of reciprocity, and perhaps particularly reciprocal altruism, is that whether or not you give help is determined by what sorts of benefits you are going to get in return. Giving is contingent on subsequently receiving. According to reciprocal altruism, the reason that cooperation can emerge in a world of selfish egoists is that cooperation is not a zero-sum game: my gain is not necessarily your loss – we can both win. In a world of cooperators/reciprocators that shun cheats, it pays to be a cooperator.

The contingency at the heart of reciprocity can take a number of forms. For instance, giving someone some food might be contingent on getting the same quantity of food in return. Or it could depend of receiving the same proportion of the stock we gave away, regardless of the absolute amount returned. Giving might also be contingent on overall levels of exchange between whole families, rather than on an individual-by-individual basis. Alternatively, giving and sharing can depend on the amount of effort that people put into solving problems such as gathering food – it is one thing to do badly despite your greatest efforts, but another to do badly through sheer idleness. So we have here four types of contingency, what Gurven calls, in order, ‘quantity’, ‘standardised quantity’ (percentage), ‘frequency’ (of exchange between families), and ‘value’ (of effort put in or some other factor). Experiments at the interface of economics and psychology have, over recent years, provided support for the role of value in shaping what people think other people deserve out of group efforts, and Gurven’s study adds to this.

A number of theories have been put forward to explain the nature of human altruism, which stands out as an anomaly in the natural world because of the levels of help and cooperation between unrelated people in human societies. It is likely that the different theories explain different aspects of human altruism. However, they do differ in the types of contingency you’d expect to see in certain cooperative and altruistic actions, and so studying them can help determine which processes are operating in which situations.

Unfortunately, little attention has been paid to the different forms of contingency and their roles in regulating altruistic behaviour. So Michael Gurven, an anthropologist at the University of California at Santa Barbara, set out to explore these issues using data previously collected by Gurven and other anthropologists in two populations: among the Ache of Paraguay, and the Hiwi of Venezuela. Through a number of statistical analyses, Gurven demonstrates that contingency does play an important role in food sharing among these populations, and also that different forms of contingency operate in different contexts.

The Ache and Hiwi live in different ecological niches, and collect and consume a range of food types (for instance, the Hiwi lived near a river and therefore had access to fish). Gurven grouped food types together, and analysed the role of contingency in governing whether and how they were shared. The Ache diet was categorised into forest foods (such as meat and honey), ‘cultigens’ (such as sweet manioc, corn and sweet potatoes) and store-bought foods (such as bread and oil); Gurven also looked at contingency in ‘all food types combined’. Contingency among the Hiwi was examined by grouping food as meat, fish, ‘other foods’, which included fruit and roots, and ‘all foods combined’.

Gurven found strong evidence for contingency in sharing meat and fish among the Hiwi, although this wasn’t seen for resources grouped as ‘other foods’ (fruit and roots). On average, for every kilogram of meat given to another family 0.69 kg was given back; for other foods, the return rate drops to 0.08 kg for every kilogram given. Among the Hiwi, the form of contingency called ‘quantity’ was the most prominent in the exchange of meat and when all resources were considered together; ‘value’ had an effect similar in magnitude, though not quite as great. The transfer of fish among the Hiwi seemed to be predominantly contingent on standardised quantity (percentage).

Among the Ache, frequency and value contingency were most important for forest foods and cultigen transfer, and value stood out as an important determinant of giving when all foods combined were considered together.

The lack of contingency in the giving of non-meat (‘other’) foods is interesting – what is it about these resources that makes people share them differently? Roots and fruits, while making up more than 40% of the Hiwi diet, are the least transferred resources. A number of factors explain why giving of these foods is less contingent than for other resources, and why they are not shared much in the first place. First, the existence and location of fruit and roots, unlike animal game, is highly predictable. This means that there is low variability in the amounts of these resources that foragers return with (that is, collecting these resources is less subject to the vagaries of chance). Second, individuals typically gather fruits and roots at the same time, and are therefore usually stocked up or not at the same time. These two factors reduce the need to exchange these foods in the first place: you’re more likely to be without meat or fish than without fruit or roots.

These anthropological results tie in with studies in behavioural economics that reveal that people are motivated by notions of fairness based on labour input into collective actions. The notions of fairness built into human psychology give rise to, and are probably reinforced by, cultural norms that explicitly spell out what is fair and what is not. Gurven suggests that thinking about the types of contingent cooperation seen in his anthropological survey could “begin to bridge the gap between the short-term calculus of reciprocal altruism and the longer-term social relationships emphasized in cultural norms.”

It is important to recognise that although reciprocal altruism and TFT are highly contingent, the finding of contingency in the food sharing of the Hiwi and Ache does not mean they are engaged in a TFT strategy. It seems that the forms of contingency observed, and the motivations driving cooperative behaviour, are the product of psychological systems, buttressed and canonised by cultural norms (and also perhaps in part shaped by them), that promote long-term collaborations in a way that TFT cannot.

The value people attach to the effort other people put into collective actions, and their altruistic intentions, has, according to Gurven, been neglected in past explorations of human cooperation in the anthropological literature. Given the recurring importance of value-based contingency found by Gurven, more attention to value should be paid in future studies. In general, the behavioural outcomes identified by anthropologists and other students of the human social sciences need to be linked up with work on the psychological underpinnings of human cooperation. A problem as complex as human altruism is surely going to require a pluralistic, inter-disciplinary approach to clearly illuminate the multifarious facets of this perennial question.

1. Gurven, M. The evolution of contingent cooperation. Current Anthropology 47, 185-192 (2006).

2. Trivers, R. L. The evolution of reciprocal altruism. In Natural Selection and Social Theory: Selected Papers of Robert Trivers 18–51 (Oxford University Press, 2002).

3. Nowak, M. & Sigmund, K. Evolution of indirect reciprocity by image scoring. Nature 393, 573–577 (1998).

4. Alexander, R. The Biology of Moral Systems (Aldine Transaction, 1987).

Friday, March 10, 2006

The Good Books

The long-list for the Aventis Prize for science books has been announced.

Monday, March 06, 2006

Have Your Say

I want to get some feedback on the stuff I’ve written for this blog to see whether I might do things differently, and I have a couple of questions. I’m interested in whether people think the posts are:

Too long and too detailed (or not detailed enough)
Too diverse in topic, making it hard to know whether you’re likely to find a new post of interest
Too infrequent, even given their typical length

If anyone wants to reply to these, or give any other feedback, you can e-mail me at danrbjones [‘@] hotmail [‘.’] com. Thanks.

Taking Stock

This blog is approaching two months old, and I’ve posted a few entries now, but as they’re mostly long they disappear way off the bottom of the page, so I thought I’d sumamrise what I’ve posted so far, in reverse chronological order.

The most recent post is on two papers looking at the nature of collaboration and altruism in humans and chimpanzees.

Here’s my coverage of a paper on the evolution of sexual reproduction, one the enduring mysteries of evolutionary biology.

This post looks at the role of unconscious automatic psychological processes, and how they can sometimes lead to more satisfying choices than conscious deliberation.

I wrote a long essay about the philosophers’ zombies, a thought experiment designed to illuminate the nature of consciousness.

A post I wrote on the biology of race generated some feedback that I replied to here.

This post looked at how your level of empathy for people in pain can be affected by whether you think the victim is a fair person or not.

I took a look at the meanings of theism, atheism and agnosticism in this post.

I started this blog with a two-part review of Richard Dawkins’s two-part programme on religion, science an atheism, The Root Of All Evil?, here and here. I also replied to a review of the programme here.

Sunday, March 05, 2006

With A Little Help From My Friends

Two new papers in Science on the collaborative tendencies of chimpanzees and human infants shed light on the nature and evolution of cooperation and altruism.

Although the image of nature as ‘red in tooth and claw’ has an established pedigree, and great popular resonance, the role of cooperation in nature has also been long recognised (1). The extreme form of cooperative behaviour that social insects, such as bees and ants, engage in, in which some individuals sacrifice reproduction seemingly for the good of the hive, posed problems for Darwin. But modern theories of the evolution of cooperation, such as W. D. Hamilton’s kin selection theory, and Robert Trivers’s idea of reciprocal altruism, have helped explain otherwise puzzling cooperative behaviour in a range of species.

But we humans stand out as an evolutionary anomaly because of our propensity to behave cooperatively or altruistically in situations that cannot easily be explained by kin selection or reciprocal altruism. Our altruistic acts often extend well beyond the confines of our nearest and dearest. We (well, some people at least) donate blood, give to charity, do voluntary work, and go out of our way to avoid affecting others with our pollution.

In fact, modern experimental results of how people behave with regard to others are increasingly leading to the view that humans are motivated by a genuine concern for others, and not merely disguised selfish interest, genetic or otherwise. At the very least, gene-based models of the evolution of cooperation might need to be augmented with studies of cultural evolution and gene–culture co-evolution (2).

There are many components to the human capacity for altruism and successful cooperation. Empathy is an important motivating factor in driving people to altruistic acts of help in response to seeing people in distress. It is also useful to have a sense of fairness, which helps to avoid being exploited in ‘collaborative’ acts. Sarah Brosnan and Frans de Waal have shown that Capuchin monkeys refuse to participate in ‘work’ if they see another monkey getting a better reward for the same labour. This effect is amplified if another monkey is openly rewarded for no effort at all in front of a working monkey (3). At a more basic level, organisms often need to understand the sort of help required by other individuals in need in order to act effectively. And if individuals are to engage in successful cooperative acts, it is useful if they can identify those with whom they can work well.

Monkey see, monkey do
The first paper in Science (4), from Alicia Melis and colleagues, looks at the last two skills in chimpanzees. The findings strongly suggest that chimps can understand when help is needed, at least in the experimental set-up used in this study, and what the appropriate thing to do is to solve the problem at hand. They also show that when selecting a partner for a cooperative endeavour, chimps pick individuals on the basis of whether they have previously had successful collaborations with them or not.

Part of the reason for exploring these skills in chimps is that, being our closest primate relatives, they can shed light on what mental faculties are unique to humans, and which are perhaps derived from a common ancestor with chimps. Faculties that are shared between chimps and humans are plausible candidates for the building blocks of human altruism, even if human social behaviour is transformed by cultural additions and modifications.

Melis and colleagues used an ingenious set up to explore the nature of collaboration in chimpanzees (see figure to the left). Two sets of experiments were undertaken. The first set looked at whether chimps recruited help more often when they needed it, and therefore whether they understood what needed to be done to solve the problem they faced. To test this, the researchers set up two experimental conditions.

In the first condition, food rewards were placed on a platform outside the test room (see figure above). A piece of rope was threaded through two loops on the food-bearing platform, and the ends extended into the test cage so that they lay 55 cm apart. A chimp (the subject) was then released into the test room. To get the food, the chimp merely needed to grab both ends of the rope, which were close by, and pull (if the chimp only pulled one end of the rope it would unthread through the loops). While the chimp pondered the problem, a partner chimp, visible to the subject, remained locked in a room adjacent to the test room. The lock to the room was a simple device. In any case, chimps had previously been introduced to the ‘pulling task’ to get the food, and also learnt to unlock the door to let another chimp out. So they could do one act (unlocking the door) in order to do the other (get the food). The researchers watched, waited, and observed what the subject did (this was called the solo condition).

In the second condition (called the collaboration condition), the ropes were placed 3 metres apart, so that the only way the chimp could get any food at all was by recruiting help from the locked-up partner to simultaneously pull on the rope (the chimps had shown they knew how to do this in training trials).

If chimps recruit help only when they need to do, so as to maximise the reward they get by acting alone, then they should have unlocked the partner more often in the collaboration condition than in the solo condition. And this is just what was found.

So this first set of experiments shows that chimps know when they need to enlist help, and when they can go it alone and reap more rewards for themselves. The second of set experiments shows that chimps can also enhance their likelihood of forming successful collaborations on the basis of previous experience with other chimps.

In this set of experiments, in addition to a partner in the same room as before, there was also a chimp in the second adjacent room. These two potential partners for the rope-pulling problem differed markedly in their skill at solving the task. The subject partner had previously had a limited number of interactions with both chimps independently in obtaining food from the platform. So the subject chimp, if it had learnt that one chimp was a better choice as a partner for solving the problem than the other chimp, would be expected to pick the better partner more often. And again, this is what was found. Interestingly, the chimps’ behaviour provided evidence that they were tracking the relative success of partners and updating their decisions on the basis of previous outcomes. The chimps basically followed a ‘win-stay/lose-shift’ strategy: if they were successful with a partner, they would pick the same chimp for the next trial, and if it was unsuccessful switched to the other (this wasn’t an absolute rule they followed, and there were exceptions).

So chimps seem to know whether they need help, and to know who to turn to when they do. It also shows that chimpanzees can adapt a new skill, such as unlocking a door, and use that to aid future collaborations (in setting a partner free to collaborate in getting food).

Of children and chimps
The second paper in Science (5), from Felix Warneken and Michael Tomasello, tackles a different set of questions. While the first paper, described above, reveals that chimps know when, and with whom, to engage in collaboration to maximise benefits to themselves, what about helping when you have nothing to gain? Humans do this all the time, from holding doors open for people behind us to picking up a book for somebody who drops one. And it is this tendency that Warneken and Tomasello explored in their experiments.

Human infants and three young chimps were used as the subjects in this study (the small number of chimps limiting the strength of conclusions that we can draw from this work). The infants were pre-linguistic 18-month olds, and they were presented with 10 situations in which an adult (a male experimenter in this case, and therefore a stranger to the child) needed help in some task. In one situation, the experimenter, while hanging up washing, drops a clothes peg, and pretends to be obstructed by the clothes wire so that he cannot reach the peg on the floor. The child can see what is happening, and can walk over, pick up the peg, and hand it to the experimenter. In another situation, the experimenter, carrying a stack of magazines, approaches a closed cabinet, and tries, unsuccessfully, to put the magazines into the cabinet but instead just hits the door. In this case, the child can walk over to the cabinet and open the doors. The 10 situations were grouped in to four categories, according to the nature of the situation presented to the child: out-of-reach, physical obstacle, wrong result, and wrong means.

The children were also tested in control conditions. In the experimental situation, the experimenter made it clear through facial expressions, bodily reactions and sounds that there was a problem, and that help was needed. In control conditions, the experimenter remained neutral and did not suggest that there was a problem.

Children were significantly more likely to help in the experimental condition in 6 out of the 10 situations – picking up clothes pegs and handing them to the experimenter, or putting fallen DVD boxes on top of a pile that the experimenter missed. As these children couldn’t speak or fully comprehend language, it is unlikely that they have merely learnt to help through verbal instruction, although social norms may well augment a tendency to help others (or, perhaps in some circumstances, curtail it).

The same studies were carried out with the three young chimps. Although the chimps tended to help in the situations in which an object was merely out of reach, they weren’t so forthcoming in tasks that required actions other than merely grabbing and passing. There are number of possible reasons for this discrepancy. Perhaps the children were simply more willing to help, and this expressed itself as greater help across a wider range of situations. Alternatively, the chimps might simply have been stumped by the problems posed – even if they had recognised that help was required, they might not have understood what the goal of the experimenter was or how to aid him. Children have pretty advanced cognitive skills, particularly in the social domain, from a young age, and this might have given them the edge in being able to provide help.

Time to sum up. Chimpanzees recruit help when they need it, and from the best available partners, suggesting that corresponding skills in humans have a perhaps ancient evolutionary origin. But chimps are not so good at providing help across situations that require different forms of help. Maybe this is because of cognitive limitations, or maybe because of altruistic limitations. Pre-linguistic children, however, are capable of recognising when someone else needs help in reaching some goal, and are willing and able to provide this help in a wide range of situations. This is a good foundation for producing adults that are also likely to provide altruistic help to others, including strangers. And this propensity can be enhanced through internalisation of social and cultural norms that promote prosocial behaviour.

But is this sort of behaviour completely non-selfish altruism? At first it would seem so, as the helper derives no immediate benefit. But that doesn’t mean there are no benefits, even if they are not immediately obvious. A reputation for being a good collaborator and an general altruist can do wonders for your social currency, and can enable you to participate in projects that might otherwise have been closed to you. In any case, a tendency to want to help is a crucial ingredient of human prosociality. The challenge still remains of fully fleshing out a theory of human altruistic behaviour.

1. See the contrasting views of ‘Darwin’s Bulldog’, T. H. Huxley, and the anarchist Prince Peter Kropotkin.

2. Fehr, E. & Fischbacher, U. The nature of human altruism. Nature 425, 785-791 (2003).

3. Brosnan, S. B. & de Waal, F. B. M. Monkeys reject unequal pay. Nature 425, 297-299 (2003).

4. Melis, A. P, Hare, B. & Tomasello, M. Chimpanzees recruit the best collaborators. Science 311, 1297-1300 (2006).

5. Warneken, F. & Tomasello, M. Altruistic helping in human infants and young chimpanzees. Science 311, 1301-1303 (2006).

Saturday, March 04, 2006

Why Sex Is Good (and not for the obvious reasons)

A new paper in Nature helps explain why sex is so ubiquitous.

The existence of sexual reproduction is one of the great mysteries of evolutionary biology. It’s widespread, but there is no consensus on what benefits it confers over asexual reproduction, which seems to be a perfectly respectable way to go about reproducing (there are many asexual species, and some species have even gone from sexual to asexual reproduction). This is not for want of candidate explanations — it is just very difficult to get the relevant evidence to adjudicate between to competing theories (1). A recently published paper in Nature, from Ricardo Azevedo and colleagues, now provides some clues to explain the conundrum of sex.

So why is sex such a puzzle? In the 1970s, John Maynard Smith and George C. Williams independently explored the problems posed by sex, which Maynard Smith summed up as the ‘twofold cost of sex’. Jeremy Cherfas and John Gribbin have summarised the problem like this:
[I]magine a population of male and female animals happily reproducing by means of sex…Now imagine that a mutant female arises, that is, one who differs genetically from the bulk of the population. She can do without males and still have young. Her offspring will all be female who, like their mother, can reproduce without the help of males, by a process called parthenogenesis (from the Greek for virgin birth). Because she does not produce males, such a female would have twice as many daughters as the other females; and because only daughters put much effort into raising offspring the mutation would spread very rapidly indeed. Within a very few generations all the females will be asexual. There is the cost of sons, dramatically brought out into the open: they halve a female’s capacity to reproduce.
This drives home the message that females that reproduce parthenogenetically (or asexually) and produce more parthenogenetic females will, other things being equal, push out sexual reproducers. But the idea that sex halves a “female’s capacity to reproduce” is perhaps worth expanding on, as phrased like that it might be misleading.

Imagine a population of 100 females and 100 males. In this idealised population, each male mates with one female, and between them have two offspring, which the female raises. This occurs generation after generation. After 5 generations, a given female would have left 32 descendants, as would each male. Now imagine a parthenogenetic female, who through virgin birth can leave 2 females as descendants; again, after 5 generations, a parthenogenetic female would leave 32 descendants, which, in terms of counting offspring, is exactly the same as in the sexual situation. This makes it clear that it is not the capacity to reproduce per se that is halved by sex, or doubled by asexual (parthenogenetic) reproduction (that is, females on average will still leave the same number of descendants. Sex does, however, reduce the per capita reproductive rate, as sex requires that two individuals get together to make one offspring, whereas in an asexual situation each individual produces each offspring alone.

The cost of sex can be expressed in different though fundamentally similar terms: by considering the fate of genes influencing sexual and asexual reproduction (the strategy made so famous by Richard Dawkins in The Selfish Gene).

Think of a simplistic model in which one gene determines whether a female reproduces sexually or asexually. Let’s assume that there are 100 females in a population (and 100 males), all of which reproduce sexually. Any given gene in a female has a 50% probability of being passed on to her offspring, so that all offspring are 50% related to their mothers and, of course, 50% related to their fathers. Now a mutant gene arises in a female that causes her to reproduce asexually. In this situation, she will be 100% related to her offspring (and the offspring will be 100% related to their mothers) — after all, she passes on all her genes to her offspring (and the mother is the only source of the offspring’s genes).

Such a gene for asexual reproduction would be present in 100% of her offspring, a guaranteed ticket to the future. This stands in stark contrast to the fate of genes in a sexual reproducer — only 50% of her genes would then be eligible for entry into future generations. For any given gene in a sexual species, including those determining whether to engage in sex or not, there is a 50% chance of being passed on. In other words, a gene for sex reduces by half the likelihood that it, and all other genes in the genome, will make it into the next generation. Therefore asexual reproduction increases by twofold the genetic representation of female genes in future generations; this, then, highlights the twofold cost of sexual reproduction. I’ve belaboured the point at bit, but it’s important to get clear on this.

In both the model suggested by Cherfas and Gribbin, and the ones sketched above, although the actual numbers of offspring left by females is the same in asexual and sexual populations, the proportion of asexual females relative to sexual females and sexual males will rise, and with it the genes for asexual reproduction instead of sexual reproduction. Extrapolated over time, the genes for sexual reproduction would be displaced by asexual variants and disappear, and all reproduction would be asexual. This leads to the same conclusion that Cherfas and Gribbin arrive at — namely, that producing sons is not in the genetic interest of females. So the problem of sex is the question of why sexual reproduction is so ubiquitous in nature. What benefits does it provide to offset its costs?

There are, as noted above, a variety of hypotheses as to what these benefits are. One strong contender is the ‘mutational deterministic hypothesis’, devised by Alexey Kondrashov (2), and it is this model that the current paper in Nature draws on.

The basic idea of the mutational deterministic hypothesis is that sex can bring harmful mutations present in two parents together in a single individual; if this individual then dies, this eliminates harmful mutations (deleterious mutations, in the argot of geneticists) from the population. Imagine a group of asexual organism reproducing away. Then a deleterious mutation arises in one individual. All descendants of this mutant will inherit the harmful gene, and carry the cost. The only way this cursed lineage can get rid of its bad ‘genetic load’ is to die out, or wait for the unlikely event of a mutation that exactly reverses the original deleterious mutation. If this lineage suffers another genetic hit, then it will be doubly afflicted, with as little scope for escape.

Sex changes this. Imagine two sexual parents, each of which carries one harmful genetic variant. If the parents have more than one offspring, then, through the lottery of sexual inheritance, some might inherit one, both or neither of the harmful mutations. The mutation-free offspring have clearly benefited from sex, and those that inherit one have fared no worse than under asexual reproduction. But what about those that get a double dose of bad mutations? What happens to them? Well, it depends on whether the effects of the mutations interact with each other, a process known as epistasis.

These genetic interaction can take a number forms. If there is no interaction, or neutral epistasis, then the combined effects of the two mutations will be the sum of the independent mutations (that is, if each mutation carried a cost of –5 ‘survival points’, having both would cost –10). Alternatively, the mutations can interact positively, or antagonistically (this nomenclature is a bit counter-intuitive, as antagonism sounds negative, so you have to pay attention!). In this case the combined effects cancel each other out to a degree, such that the overall effect may be less than the sum of the individual effects (say, anywhere between –9 and –6 survival points), or even their individual costs (anywhere between 0 and –4 survival points). Finally, the effects may interact negatively, or synergistically, in which cause the combined effect is greater than the sum (a lower number than –10 survival points: –11, –12 and so on).

If harmful mutations interact synergistically — that is, enhance the effects of each other — then sex can potentially pay the two-fold cost it imposes over asexual reproduction by purging lineages of harmful mutations. Here’s how. If possessing either mutation A or B alone merely lowers fitness (survival plus reproduction), these mutations may hang around in lineages for a while and continually lower the fitness of all individuals in that lineage, constantly dragging each individual down. Synergy between the mutations provides a way out of this. In the most extreme case, individuals that get a double dose, or multiple doses, of mutations are absolutely unviable, and die right away. In this case, a whole clutch of bad mutations can be wiped out in one go. At the same time, other offspring may, through the luck of sexual inheritance, be mutation free — in which case, the bad genes have be removed from that lineage. This is a potentially powerful benefit for maintaining sexual reproduction.

One obvious question in light of all this is whether epistatic interactions between mutations are typically positive, neutral or negative. The answer is that in experiments you see all sorts of interactions, which hasn’t exactly helped to clarify what role epistatic interactions might play in the evolution of sex.

Previous work using computational models of evolution has suggested that natural selection can shape the nature of epistatic interactions, so under some (artificial) selective regimes natural selection can favour positive (antagonistic) epistasis, and in another negative (synergistic) epistasis. One way that the evolution of epistasis can be affected is if the genomes of organisms — that is, their entire collection of genes — and the networks of protein products they encode are selected to be ‘robust’. Robust in this sense means being insensitive to the effects of mutations. Selecting for robustness affects the nature of epistatic interactions.

Robustness is a good design feature: if you’ve got a complex system with lots of interacting parts, you don’t want the fate of the entire system to be placed in the hands of every single part. It’s good to have some mechanism for coping when parts go wrong.

It turns out that if you select for robustness in computer simulations, you produce as a correlated response increased negative (synergistic) epistasis. Another way of saying this is that robustness is negatively correlated with the ‘direction of epistasis’: when robustness is positive, epistasis is negative (taking positive and negative to represent different directions)*.

Genomes in sexually reproducing species do not only need to be robust against mutations. They also need to be robust against the genetic shuffling that occurs between generations when sperm and eggs recombine and mix their genes, process that is characteristic of sexual reproduction. This is ‘recombinational’ robustness. It has been proposed that sexual reproduction, which essentially means more recombination, imposes stronger selection for genetic robustness than asexual reproduction does.

And this is where the new study comes in — it probes this very idea. It’s not an experiment, at least not in the sense of involving real organisms with real genes. Instead, the researchers have used a computational model of artificial gene networks to get some purchase on whether sex (or recombination) selects for increased robustness.

The details of the model used in the new paper are complicated, but a few salient points should be noted. The model basically simulates a population of individuals (actually gene networks), and there is a certain amount of genetic variation between ‘individuals’ for evolution to work on. Individuals can also mutate to create new variation, and in sexual versions of the population recombination between individuals (mixing up of parental genes) takes place.

This model has previously been shown to produce, or evolve, genetic robustness if the gene networks are selected on the basis of whether they produce stable patterns of gene expression. Genes encode protein products, and these can in turn affect the activity of other genes (and sometimes also the activity of the genes encoding them). Genetic networks evolve to produce patterns of gene expression that achieve functional ends, like building limbs and regulating our metabolism. If these are easily perturbed they’ll have difficulty producing the desired outcome. And so gene-expression patterns should be stable, or at least respond in appropriate ways when perturbed, to produce functional organisms, or at least functional gene networks. When gene networks that produce stable gene-expression patterns are selected for, robustness emerges — that is, the networks evolve the capacity to maintain stable patterns of gene expression if the face of perturbations.

In this particular application of the model, the role of recombination in producing robustness was explored, using gene networks selected for their capacity to produce stable gene-expression patterns. What’s more, the researchers also looked at whether recombination, through producing robustness, could influence the direction of epistatic interactions (that is, whether there were positive, neutral or negative) that evolved.

Because of the way the model was set up, populations should be subjected to selection for both mutational robustness (insensitivity to mutations) and recombinational robustness (insensitivity to the effects of bring genes into new combinations through genetic recombination).

By tweaking the model, Azevedo and colleagues were able to tease apart the effects of sexual reproduction on selection for mutational and recombinational robustness. They found that to the extent that mutational robustness evolved in sexual populations, it was not as a result of direct selection for this type of robustness. Instead, mutational robustness was found to be a correlated response to selection for recombinational robustness. So selection for recombinational robustness produces a correlated response of mutational robustness. Another important finding is that in sexual populations in which mutational robustness evolved, negative, or less positive, epistasis also evolved. As the authors conclude:
“Taken together, these results confirm that mutational robustness and negative epistasis both evolved in response to selection for recombinational robustness.”
There are obviously limitations to this study. Firstly, it is very simple compared to the complexity of the genomes of multi-cellular plants and animals. Secondly, recombination is already present in the model — so this, the central feature of sex, did not have to evolve but was already there. Perhaps in this regard the paper contributes more to our understanding of the maintenance of sex, rather than its origins.

However, it is an interesting thought that sexual reproduction seems to create conditions that favour its own maintenance. Perhaps sex evolved in part because recombination lead to the evolution of genetic robustness, enabling extremely complex genomes to evolve, and this robustness resulted in a correlated evolution of negative (or synergistic) epistasis. Then sex could deliver the benefits spelled out by the mutational deterministic hypothesis. The synergistic interaction of harmful mutations would enable sex to purge them from the genomes of sexually reproducing organism — and therefore to pay its way.

*This might seem odd. Let me explain if it doesn’t. Mutational robustness, or insensitivity to mutations, is a capacity to dampen down the harmful effects of mutations. So any mechanism that did that would seem to be associated with robustness. And that seems to be what positive (antagonistic) epistasis does — the harmful effects of combined mutations antagonise each other, and cancel one another out to an extent. This is a sort of damping down. But in fact negative epistasis is seen to emerge alongside robustness.

The reason for this is difficult to explain, but it seems to be a reliable finding. One possibility is that if genomes have on average only one or two mutations, then mutational robustness can evolve through positive epistasis for the smaller number of mutations. This has the effect of changing the shape of a graph plotting fitness against mutational load (if we assume that previously there was no directional epistasis - that is,
neutral epistasis ). In fact, the new curve looks like a curve of negative epistasis, but from a different starting point. This isn’t, I realise, terribly helpful without some images. But in sum, genomes might evolve to be more robust to the presence of the small average number of mutations but pay the price of being less robust in the face of many mutations (thanks to Ricardo Azevedo for this point, personal communication).

1. A relatively accessible introduction to some of the ideas about the evolution can be found in: Cherfas, J. & Gribbin, J. The Mating Game: In Search of the Meaning of Sex (Penguin, 2001).

2. Kondrashov, A. S. Deleterious mutations and the evolution of sexual reproduction. Nature 336, 435–440 (1988).