Reward creates oculomotor salience

Wouldn’t that be a good way of studying evolution in action over a few generations? One would think so. In particular, it is possible to measure all three components of the breeder’s equation, and see directly whether R = h2S. But, quite often, it appears that R does not equal h2S. For example, a study on antler size in red deer showed that red deer with larger antlers had more offspring than red deer with smaller antlers, and antler size has a high heritability. Yet no response to selection, R, could be detected. How is this possible? The problem is not in the measurement of h2 or R, but in the measurement of S. In artificial selection, where individuals are selected by the experimenter on the basis of their value of the trait, it is the trait itself that determines reproduction, and any source of variation in the trait will affect which individuals are chosen. But, in studies of natural selection, all that is seen is a correlation between measured fitness and the trait. In this case, therefore, the trait itself does not necessarily cause the fitness differences. An environmental insult, such as disease, could simultaneously lower the trait value and also survivorship and/or reproduction, in other words, fitness. The consequence is that it is possible to have a trait–fitness correlation, arising from a purely environmental covariance, which creates the false impression of selection, without there being any correlation between fitness and the breeding value of the trait. What matters is the genetic correlation between fitness and the trait.