Since most MUDs have classes to determine the main play style of a character, race is often something that is selected when a player is created, and then is of limited importance from that point on. Sometime, race will mean the difference of an extra attack (such as a bite), or will mean a few extra points of one stat at the expense of another. The effect is that most players will either just pick human, or they will pick a race that maximizes their class. That approach leads to race becoming little more than a minor boost for players who know what the best race is for a given class, and simply select that race.
Race should be both balanced, and meaningful. This means that race should confer benefits or weaknesses that are equal for all races. A hobbit warrior should be just as strong as a canis warrior. Just not in the same way. The same with a human; human cannot simply be a default race.
Creating this balance is the only way to ensure a diversity of race and class combinations. It is also the only way to make race worth the time of having it. If one races is better than the rest for a mage, all the best players will make mages of that class. If every class has a best race, there is no reason to have race at-all.
