Wildebeest arrive at the Mara River in their tens of thousands, and gather waiting to cross. For days their numbers can be building up and anticipation grows but many times, for no apparent reason, they turn and wander away from the water’s edge. Eventually the wildebeest will choose a crossing point, something that can vary from year to year and cannot be predicted with any accuracy. Usually the chosen point will be a fairly placid stretch of water without too much predator-concealing vegetation in the far side, although occasionally they will choose seemingly suicidal places and drown in their hundreds. Perhaps, once again, this is because crossing places are genetically imprinted in the minds of the animals.