But it isn’t only your own children who contain copies of your genes. So do your grandchildren, nieces, nephews, sisters and brothers. The more distant the relationship, the lower the probability that a gene will be shared. A gene for saving the life of your child or your sister has a 50 per cent chance of being shared by the child or sister. A gene for saving the life of a nephew has a 25 per cent chance of being in the body of the nephew saved. A gene for saving the life of a first cousin has a 12.5 per cent chance of being shared by the cousin saved.*2
So natural selection favours individuals who take slight risks to save the life of, or otherwise help, a first cousin. But it favours taking a greater risk to save the life of a niece. And an even greater risk to save the life of a sister or a son. Not just to save their life directly, either, but to help them in any way, like feeding them, or protecting them from predators or sheltering them from the weather.
Theoretically, natural selection favours feeding a brother as much as it favours feeding a son. But in practice there are more opportunities to usefully feed a son or a daughter than a brother or sister. This is why parental care is more common than sibling care. Sibling care really comes into its own in social insects like ants, bees, wasps and termites. Also certain birds like acorn woodpeckers in America, and mammals like naked mole rats in Africa.
Animals can’t be expected to ‘know’ who their close relatives are. Natural selection of genes doesn’t build into bird brains a rule like ‘Feed your children’. Instead, the brain rule is more like ‘Feed anything that opens its mouth and squawks inside your nest’. That’s how cuckoos get away with laying their eggs in the nests of other birds. The baby cuckoo usually hatches first, and it throws out the eggs that were laid by the foster mother. The foster parent obeys the rule that its genes planted in its brain: ‘Feed anything that opens its mouth and squawks in your nest.’ That’s exactly what the baby cuckoo does – and so it gets fed.
Our wild ancestors probably lived in small, roving bands like baboons. Later, in small villages. Both would have been equivalent to extended families. Almost everybody in the village or band would have been your uncle or your cousin or your niece. So a brain rule like ‘Be nice to everyone’ would have been equivalent to ‘Be nice to your genetic relatives’. Most of us no longer live in small villages. It’s no longer true that everyone you know is a cousin or a niece or other relative. But the rule ‘Be nice to everyone’ still lurks in our brains. This could be part of the Darwinian reason why we have a tendency to be friendly to others.
Unfortunately, there is a flip side to the coin. In the brains of our ancestors in their small bands or villages, the rule ‘Be hostile to anyone you’ve never met before’ would have been equivalent to ‘Be hostile to anyone who is not a relative’. Or ‘Be hostile to anyone who looks very different from you and the people you know’. Such brain rules could provide the biological origins of racial prejudice. Or of hostility to anybody perceived as ‘other’, like recent immigrants.
But unconscious rules of thumb aren’t all the human brain has to offer. Unlike ants and acorn woodpeckers, humans have the brain power, especially aided by language, to actually know who is related to whom. The brain rule ‘Be nice to everyone’ could be superseded by a more specific brain rule: ‘Be nice to individuals whom you actually know are your relatives.’
The !Kung peoples of the Kalahari desert are thought to be as close as any modern people to our ancestors. The light brown !Kung were in South Africa long before black invaders arrived from the North. They are hunters and gatherers who live in family groups. Each group claims ownership of a hunting territory. If a man strays into the territory of a rival group, he is in danger unless he can persuade the owners that he is related to somebody in their group. On one occasion, a man called Gao was caught in an area called Khadum, outside his home territory. The residents of Khadum were hostile. But Gao managed to persuade them that someone in Khadum had the same name as Gao’s father. And it turned out that someone else in Khadum was also called Gao. This suggested that they shared relatives. The Khadum people then accepted Gao and gave him food.
The mountains in the centre of New Guinea were isolated from the rest of the world for thousands of years. In the 1930s, Australian and American explorers were amazed to discover about a million people, the New Guinea highlanders, who had never seen anyone from the outside world. The first encounters were pretty frightening for both sides. Archaeology suggests that the New Guinea highlanders had been there for about fifty thousand years. Some tribes were still hunters and gatherers like the !Kung. Other tribes had shifted to growing crops around nine thousand years ago, only a little later than agriculture began, independently, in the Middle East, India, China and Central America. The New Guinea highlanders are divided into hundreds of tribes speaking mutually unintelligible languages. And they are hostile to members of other tribes. As with the !Kung, that even includes hostility to neighbouring bands belonging to the same tribe but different kin groups. In some areas, men who wander into territory belonging to a different kin group are in danger of being killed. They can be saved by a conversation in which they explore whether they have any cousins or other relatives in common. If they can identify a shared kinsman they may part amicably. If not, a fight, possibly to the death, is likely.
In addition to kinship, there is another way in which natural selection can favour niceness, one that might be more important than kinship. The theory here is called Reciprocal Altruism. If I do you a good turn today, you are likely to do me a good turn tomorrow. And vice versa. That’s ‘reciprocation’. And ‘altruism’ is another word for being nice. So ‘reciprocal altruism’ means being nice back to someone who is nice to you.
Reciprocal altruism doesn’t need conscious awareness. Natural selection can favour genes that build brains that reciprocate, even though they don’t realize it. A scientist called Gerald Wilkinson did a nice study of vampire bats. These bats feed on blood, the blood of larger animals such as cows. They roost in caves during the day, and come out by night to search for food. Victims are quite difficult to find, but if a bat succeeds in finding one there is plenty of blood. So much so, that the vampire gorges itself and flies home to its daytime cave with a surplus in its stomach. But a bat that fails to find a victim is in danger of starving to death. Small bats live much closer to the borderline of dangerous starvation than we do, and Wilkinson convincingly demonstrated this.
When the bats return to the cave after a night’s hunting, some of them will be starving. Others will have a surplus. Starving bats beg from gorged bats, who vomit up some of the blood in their stomachs to feed the starving ones. The next day the roles may be reversed. The ones that had been lucky the previous night may now be starving, and vice versa. So theoretically, each individual bat can benefit from being generous after a good night’s foraging, in the expectation of repayment after a bad night.
Now, Wilkinson did a clever experiment. He worked with captive bats, taken from two different caves. Bats from the same cave knew each other but didn’t know those from the other cave. Wilkinson experimentally starved one bat at a time. Then he put it with other bats to see if they would feed it. Sometimes he put it with familiar ‘friends’. Other times he put the experimental bat with strangers from a different cave. Consistently, the result tended to be the same: if they already knew the starved bat, yes, they’d feed it; if they didn’t know it – if it came from the ‘wrong’ cave – they wouldn’t. Of course, it could also be that bats from the same cave were genetically related. Later work by Wilkinson and a colleague showed that reciprocation – paying back good turns – is more important than kinship in this case.
Wilkinson’s result probably makes total sense to you. Because you are human and that’s how humans often behave. We have a strong sense of who has done us a good turn. And we know to whom we have done a favour. We expect to be paid back. We feel a sense of debt that needs repaying, and a sense of guilt if we fail t
o do so. And we feel resentment, feel let down, if somebody fails to repay a debt or a good turn.
Now think back to our distant ancestral past. Put yourself in the position of somebody living in one of those small villages or bands. Not only would you know everybody and remember debts and obligations between particular individuals. You’d also know that you are probably going to live in the same village for the rest of your life. Everyone in the village is a possible giver of favours for a long time into the future. The brain rule ‘Be nice to everyone, at least at first or until you have good reason not to trust them’ could well be built in by natural selection. You never know when you may need a good turn repaid to you. And it’s plausible that our brains today have inherited the same brain rule from our ancestors. Even if we now live in big cities where we keep meeting people we are never going to meet again, we still have the brain rule to be nice to everybody unless there’s a good reason not to.
The idea of reciprocation, of exchange of favours, is at the root of all trade. Nowadays, few of us grow our own food, weave our own clothes, propel ourselves from place to place with our own muscle power. Our food comes from farms which may be on the other side of the world. We buy the clothes we wear, get around in a car or on a bicycle which we haven’t the faintest clue how to make. We board a train or plane which was made in a factory by hundreds of other humans, not one of whom probably knew how the whole thing was put together. What we offer in exchange for all these things is money. And we’ve earned that money by doing whatever it is we can do, writing books and giving lectures in my case, curing people in the case of a doctor, arguing in the case of a lawyer, fixing cars in the case of a garage mechanic.
Most of us would have a hard time surviving if we were transported back ten thousand years to the world of our ancestors. Back then, most people grew or found, dug up or hunted their food. In the Stone Age it’s possible that every man made his own spear. But there would have been expert flint-knappers who made especially sharp spear points. At the same time there may have been expert hunters who could throw a spear hard and accurately, but were not skilled at making spears in the first place. What could be more natural than an exchange of favours? You make me a good sharp spear and I’ll give you some of the meat that I catch with it.
Later, in the Bronze Age and then in the Iron Age, specialist smiths offered metal spears in exchange for meat. Specialist farmers offered crops to the smiths, in exchange for the digging tools that they needed to cultivate them. Later still, exchange became indirect. Instead of ‘I’ll give you food if you make me the tools to get the food’, people gave money, or its equivalent, such as a written IOU as a token of a promise to repay the debt in the future.
Nowadays direct barter (swapping) which doesn’t involve money is rare. It’s even illegal in a lot of places because it can’t be taxed. But our entire life is dominated by our dependence on other people with different skills. And the brain rule ‘When in doubt, be nice’ is still present in our brains. Along with other equally ancient accompanying brain rules such as ‘Be prepared to be suspicious unless you have built up a relationship of trust’.
So there does indeed seem to be some Darwinian pressure to be nice, which could serve as the original basis for our sense of right and wrong. But I think it’s swamped by later learned morals, such as we discussed in Chapter 6. And nothing in this chapter has changed the conclusion of Chapter 5: we don’t need God to be good.
*1For example, Jonathan Haidt in The Righteous Mind (London, Penguin, 2012) and Yuval Noah Harari in Sapiens (London, Vintage, 2014).
*2Those figures have to be understood properly. It’s a little tricky. You may have read that most of our genes are shared by everybody anyway. That’s true, and we also share a majority of our genes with chimpanzees and many other animals. The figures I have given for relatives like cousins refer to the probability of a gene being shared by a relative over and above a kind of ‘baseline’ probability that everybody in the population shares it.
Before Darwin came along, it seemed absurd to almost everyone that the beauty and complexity of the living world could have come into being without a designer. It required courage to contemplate even the possibility. Darwin had that courage, and we now know he was right. There are still unsolved problems in science – gaps in what we so far understand. And some people are tempted to say the same kinds of thing that were said about life before Darwin came along. ‘We don’t yet understand how the evolutionary process began in the first place, so God must have started it.’ ‘Nobody knows how the universe began, so God must have made it.’ ‘We don’t know where the laws of physics come from, so God must have made them up.’ Wherever there is a gap in our understanding, people try to plug the gap with God. But the trouble with gaps is that science has the annoying habit of coming along and filling them. Darwin filled the biggest gap of all. And we should have the courage to expect that science will eventually fill the gaps that remain. That is the theme of this final chapter.
It used to be simple common sense that living things had to be created by God. Darwin exploded that particular piece of common sense. This chapter sets out to undermine our confidence in common sense, beginning with relatively trivial examples and moving on to more important ones. Each example concludes with the refrain ‘You cannot be serious!’ (it’s a memorable quote from the great tennis player John McEnroe, who frequently used it to query dubious line decisions). We then return to the bigger example: the apparent common sense that says there must be a God to explain the universe’s origin and other so-far unsolved problems.
In 2014, a teenager was caught on camera urinating into a reservoir in America. The local water authority therefore took the decision to drain the reservoir and clean it at an estimated cost of $36,000. The volume of water drained was about 140 million litres. The volume of urine was perhaps about a tenth of a litre. So the ratio of urine to water in the reservoir was less than one part in a billion. There were dead birds and debris in the reservoir, and presumably plenty of animals had urinated into it without anyone noticing. But such was the ‘yuck’ reaction many people felt, the fact that a single human was known to have peed in the reservoir was enough to get it drained and cleaned. Is that sensible? What would you have done if you’d been in charge of the reservoir?
Every time you drink a glass of water, there’s a high chance you’ll drink at least one molecule that passed through the bladder of Julius Caesar.
You cannot be serious! But it’s true.
Here’s the reasoning. All the water in the world is continuously being recycled by evaporation, rain, rivers and so on. Most of it is in the sea at any one time, and all the rest of the world’s water gets circulated through the sea as the decades go by. The number of water molecules in a glassful is about 10 trillion trillion. The total volume of water on the planet is about 1.4 billion cubic kilometres, and that corresponds to only about 4 trillion glassfuls. I say ‘only’ because 4 trillion is a tiny number compared to the 10 trillion trillion molecules in a glassful. So there are trillions of times more molecules in each glassful than there are glassfuls in the world.
Which is why it’s safe to say you’ve drunk some of Julius Caesar’s pee. Of course, there’s nothing special about Julius Caesar. You could say the same of his friend Cleopatra. Or Jesus. Or anybody, provided there’s been enough time for recycling to have taken place. And what’s true of a glassful is true many times over of a reservoir. That American reservoir didn’t only contain the urine of the teenager who was caught peeing in it. It contained the urine of millions of people, including Attila the Hun and William the Conqueror and very possibly you too.
Air is recycled in the same kind of way as water, only faster, and the same kind of calculation works here too. The number of molecules of air in a lung is hugely greater than the number of lungs in the world. You have almost certainly breathed in atoms that were breathed out by Adolf Hitler. And Hitler’s secretary reported that he h
ad bad breath.
Science can be very surprising. We’re talking about the courage you need in order to cope with the surprises. Courage that should be applied to the mysteries that remain unsolved.
T. H. Huxley (Darwin’s friend, whom we met in Chapter 1) said: ‘Science is nothing but trained and organized common sense.’ But I’m not sure he was right. The stories I’m telling in this chapter seem to defy common sense. Galileo defied common sense when he showed that, air resistance apart (you have to do the experiment in a vacuum), a cannonball and a feather, when dropped from a height, will hit the ground at the same moment.
You cannot be serious, Galileo! But it’s true.
Here’s why Galileo was right. According to Isaac Newton, every object in the universe is attracted to every other object by gravity. The force of the attraction is proportional to the masses of the two objects (think of mass, for the moment, as rather like weight – there is a difference, but we’ll come to that in a moment) multiplied together. The cannonball is much more massive than the feather, so gravity will exert a stronger force on it. But the cannonball needs more force than the feather to accelerate it to the same velocity. The two exactly cancel out, with the result that feather and cannonball hit the ground together.
I said I’d clarify why mass is not the same as weight. On our planet, the mass of an object, such as a man, is the same as his weight, say 75 kilograms. But in the space station, the man is weightless. His weight is zero, while his mass is still 75 kilograms. A cannonball in the space station would float like a balloon. But you’d know it had plenty of mass if you tried to throw it across the cabin. It would need a lot of effort. As you shoved it, unless you were supported by a wall, you’d simultaneously shove yourself in the opposite direction. Not at all like a balloon. And when the cannonball hit the wall on the other side of the cabin it would crash in a ‘massive’, clunking way and might break something. If it hit somebody on the head it would hurt them (again, not like a balloon), even though both the cannonball and the head are weightless. The weight of a cannonball is a measure of the downward pull of Earth’s gravity on the ball. Its mass is a measure of the total amount of matter it contains. If you were to weigh the cannonball in the space station, the weighing machine and the cannonball would both float around freely, so the cannonball would not exert any pressure on the weighing machine. It would have a weight of zero.
Outgrowing God Page 18