|MadSci Network: Zoology|
Long or large ears that can be pointed up can receive sounds from far away. Animals that have fast predators, for example, rabbits hunted by foxes, benefit from having long ears that help them hear their predators before a predator comes within a striking distance. On the other hand, animals that spend most of their time underground, such as moles, don't have big ears, probably because they don't really have predators and, big ears would probably hinder movement underground. The long tails of some monkeys are used to hold onto tree branches, whereas the long tails of cats may be used for balance. Connected toes, like those of ducks, are good for swimming, whereas separate and long toes may be good for grabbing onto tree branches. If one closely examines the life style and habitat of an animal one may figure out the adaptive value of the shape and size of a particular organ. However, one must keep in mind that opposing factors may have been involved during the evolution of an organ. For example, the long tail of an animal may help it hang down from trees, but at the same time, it may present its predator with something to grab onto. In cases like that natural selection may have resulted in a structure that balances the requirements of different factors. Also keep in mind that every organ costs energy and material to build and maintain it. And, the energy and materials saved by not building an organ may be used to develop some other part of the body that is more essential for survival or to produce more offspring. Therefore, if an organ is not needed or used, it is likely to become smaller or totally disappear. Thus, sometimes the reason why an animal has short ears or a short tail may be not because short ears or tails are good for a particular activity, but because the animal doesn't need long ears or a long tail. For example, animals that live underground or in caves usually have poor eyesight or are totally blind. In their cases, being blind is not good for anything other than for saving resources that may instead be used to better develop some other part of the body or to produce more babies.
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