Some clear examples of selection that has gone too far can be found in dog breeding. This is partly because selective breeding in dogs has a long history, but mainly because some dog breeds are selected mainly on looks. And most extreme looks tend to be considered the best, so selection in those breeds has been, and still is, on extreme looks (for some examples see below). The fact that shape of the skull in some breeds make it difficult for them to eat normal food because of the upper jaw being much shorter than the lower jaw, such as in case of the Boxer or the Bulldog, or breathing, such as in case of all breeds with a short upper jaw resulting in a flat face, or give birth or even mate without medical intervention (e.g. Bulldog), or where there is a risk that the eyes pop out of the socket because the skull is too small for their eyes (e.g. Pekinese, Chihuahua), are clear examples of selection being taken too far. And most of these examples are only related to the skull. Other breed characteristics that are not increasing the dog's wellbeing are, for example, too long ears so that infections are common (e.g. Basset Hound), or long back and neck so that intervertebral disc disease has become common (e.g. Dachshund), or too much skin so that inflammation in between the folds becomes common (e.g. Bulldog), or sloping back so that hip problems are common (e.g. German Shepherd Dog). All examples relate to selective breeding and taking breeds more and more too an extreme, because that is what you win the show with. Looking back only we realise that we have gone too far. And that realisation comes only very slowly because people get used to animals with certain features. They don't consider them abnormal for a very long time. Important is to realise that these effects can be reversed by selecting in the opposite direction.
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