Some animals are 'nice' to each other. Vampire bats, for example, have been shown to share meals. These animals live life on the edge. If a bat fails to find a meal it is often unable to survive until the next evening's hunting. A bat that has fed well, though, has more than enough to survive, and could easily spare some of its meal. So sometimes a full bat will regurgitate some of its meal to another that is starving.
But why should one bat share with another? Bats within a colony are not necessarily relatives, and so there seems to be no reason why they should be so charitable. Needless to say, there is a good reason.
These animals are showing behaviour known as 'reciprocal altruism', which simply means that they lend each other favours in the expectation that the favours will be repaid some time in the future. A bat which one day might be bloated by a great meal, might on another evening be less lucky and be in need of help itself. By being generous one day at little cost to itself, it might be saved from starvation the next by another bat returning the favour.
There is a game called 'Prisoner's Dilemma' that can be used to understand the conditions under which this process works. In the game, two suspects have been arrested for a crime and the police question them in separate rooms. The police offer them each a deal. If they don't co-operate with each other (i.e. they give the police evidence that the other person is guilty) then they will be rewarded and the other person will be put away for the crime. If they both fail to co-operate, and give evidence against each other then they will both get locked up (although they will get a lesser sentence), but if they both co-operate with each other by keeping quiet then the police have no evidence and they will eventually both be released.
In the game, each player gets a different number of points depending on each of the four possible outcomes. These points are represented as a grid, called a 'payoff matrix'. For example:
 |
You cooperate |
You do not cooperate |
| I co-operate | We both get off (score 3 each) | I get done (score -1), and you get off with a reward (score 5) |
| I do not co-operate | You get done (score -1) and I get off with a reward (score 5) | We both get the punishment (score 1) |
Now, if the game is a one-off then a player doesn't have that much choice. If he chooses not to co-operate then he can score either 5 or 1, if he co-operates then he can only score either 3 or -1. So his obvious choice would be not to co-operate. But if the game is played over and over again, things change. If both players carry on failing to co-operate, they will both carry on scoring 1 each on every move, but if they both started co-operating, they would start scoring 3 each. So, players who start co-operating with each other might actually be able to start building up a higher score than those who don't.
For the bats the risk of starvation if they do not feed is very high, while the cost of co-operating is low, so it should be no surprise to us that they have come to co-operate with each other, with every bat benefiting from the arrangement. This sort of situation faces animals all the time, and by understanding what the rewards and costs are to them in each case, we can understand the way they behave.
Some animals are 'nice' to each other. Vampire bats, for example, have been shown to share meals. These animals live life on the edge. If a bat fails to find a meal it is often unable to survive until the next evening's hunting. A bat that has fed well, though, has more than enough to survive, and could easily spare some of its meal. So sometimes a full bat will regurgitate some of its meal to another that is starving.
Australia is the country with the most domestic sheep, and India has the largest stock of cattle.