This is a pretty interesting video that shows that monkeys share some of the same irrational trading tendencies as humans do.
In the 'monkey market' experiment, the monkeys showed a bias towards avoiding risk when they were faced with a choice between a predictable small gain and a larger, but less certain gain.
However, when forced to choose between predictable small losses and larger, but less certain losses, the monkeys' behavior changes from risk-averse to risk-seeking and they instead prefer to take the risk of a larger, but uncertain loss instead of a smaller but certain loss. Apparently, just like people, monkeys hate to lose.
This sounds a lot like the tendencies of human traders to want to stay in losing trades hoping for price to come back (accepting a chance of greater loss instead of taking the predictable small loss), instead of taking the small loss and reducing risk. It also appears similar to the instinct to close out winning trades with a small profit rather than risk losing the small profit already won.