考研英语阅读理解基本素材经济学人科技类(2)

Double or quits?

Dr Kurzban and Dr Houser were interested in the outcomes of what are known as public-goods games. In their particular case they chose a game that involved four people who had never met (and who interacted via a computer) making decisions about their own self-interest that involved assessing the behaviour of others. Each player was given a number of virtual tokens, redeemable for money at the end of the game. A player could keep some or all of these tokens. Any not kept were put into a pool, to be shared among group members. After the initial contributions had been made, the game continued for a random number of turns, with each player, in turn, being able to add to or subtract from his contribution to the pool. When the game ended, the value of the pool was doubled, and the new, doubled value was divided into four equal parts and given to the players, along with the value of any tokens they had held on to. If everybody trusts each other, therefore, they will all be able to double their money. But a sucker who puts all his money into the pool when no one else has contributed at all will end up with only half what he started with.

This is a typical example of the sort of game that economists investigating game theory revel in, and both theory and practice suggests that a player can take one of three approaches in such a game:

co-operate with his opponents to maximise group benefits (but at the risk of being suckered), free-ride (ie, try to sucker co-operators) or reciprocate (ie, co-operate with those who show signs of being co-operative, but not with free-riders). Previous investigations of such strategies, though, have focused mainly on two-player games, in which strategy need be developed only in a quite simple context. The situation Dr Kurzban and Dr Houser created was a little more like real life. They wanted to see whether the behavioural types were clear-cut in the face of multiple opponents who might be playing different strategies, whether those types were stable, and whether they had the same average pay-off.

The last point is crucial to the theory of evolutionarily stable strategies. Individual strategies are not expected to be equally represented in a population. Instead, they should appear in proportions that equalise their pay-offs to those who play them. A strategy can be advantageous when rare and disadvantageous when common. The proportions in the population when all strategies are equally advantageous represent the equilibrium.

And that was what happened. The researchers were able to divide their subjects very cleanly into co-operators, free-riders and reciprocators, based on how many tokens they contributed to the pool, and how they reacted to the collective contributions of others. Of 84 participants, 81 fell unambiguously into one of the three categories. Having established who was who, they then created “bespoke” games, to test whether people changed strategy. They did not. Dr Kurban and Dr Houser were thus able to predict the outcomes of these games quite reliably. And the three strategies did, indeed, have the same average pay-offs to the individuals who played them—though only 13% were co-operators, 20% free-riders and 63% reciprocators.

This is only a preliminary result, but it is intriguing. It suggests that people's approaches to cooperation with their fellows are, indeed, evolutionarily stable. Of course, it is a long stretch from showing equal success in a laboratory game to showing it in the mating game that determines evolutionary outcomes. But it is good to know that in this context at least, nice guys do not come last. They do just as well as the nasty guys and, indeed, as the wary majority.

Passage 4

Moon river?

The latest news from Titan

A PICTURE may be worth a thousand words. But when the picture in question is of an alien world, it is difficult to be sure what those thousand words should be. And in the case of the images that have arrived from Titan, Saturn's largest moon, that world is very alien indeed.

On January 14th Huygens, a space probe built by the European Space Agency (ESA), landed on Titan and began to deliver its precious cargo of data to anxiously waiting scientists. The most striking finding so far is a picture taken as the probe descended. It appears to show pale hills crisscrossed with drainage channels containing dark material, leading to a wide, flat darker region. The landing site itself produced less striking, but still significant images. It is flat, strewn with rounded pebbles and

appears to be a dry riverbed.

On Earth, or even on Mars, drainage channels and rounded pebbles would be taken as evidence for the erosive effects of liquid water. But at -180°C, Titan is too cold for water to be liquid. It is, however, not too cold for various hydrocarbons to be so (indeed, the most likely candidates, methane and ethane, are gases at terrestrial temperatures). Many people have suggested that Titan's dark regions might be lakes made of such hydrocarbons, or of tar that is composed of hydrocarbons which are too cold to be truly liquid, but have not frozen solid. The presence of hydrocarbons in Titan's atmosphere was confirmed on the probe's journey through it. Huygens's instruments detected both methane and ethane. But the pebbles in the picture probably are made of water—in the form of ice.

Because all of the raw images from Huygens were immediately made available to the public via the internet, amateurs have been racing ESA and its American cousin NASA to create processed, composite images. Some scientists say that a glitch led ESA to publish more data than it had originally intended, something that ESA denies. Nevertheless, a few minutes after the Huygens data were published on one website, they were mysteriously yanked off the web again.