An arrangement of roses, popular decorative flowers whose wild varieties have many more and larger thorns than do domesticated varieties.
These lemons were bred for thick skins to make them easier to ship.
This dog was bred to meet people's needs for a small, friendly housepet. It could never survive in the wild. Imagine this dog (a distant domesticated relative of the wolf) coming up against a moose.
Chickens are bred to produce many eggs. One would think that this trait would be selected for in nature: more eggs means more surviving offspring. However, in nature, a balance was reached between many offspring and the chicken being able to care for the young, enabling more of them to survive. This balance is ignored by humans, who's interest is not the survival of the chickens on their own.
There are many ways in which breeding is different from natural selection. First of all, breeding is a lot more controlled, direct, and efficient towards a single goal. Animals or plants are picked out of a group and separated by people, which leads to more rapid changes. Natural selection is a much slower process. Some die, some live, but a few more of the less suited organisms die. Sometimes conditions are less harsh and more survive in general, and sometimes conditions change. In every way, natural selection is slower and less efficient than breeding. Also, breeding starts out with a more direct goal. A breeder might say, "I am going to breed these goats for long hair." Whereas in nature it does not matter how they changed, as long as they ended up better adapted, in this case better able to keep warm.
Another difference is that breeding is only for the needs of man, so often traits are bred into organisms which would not be selected for naturally. Here are six examples:
1. People breed goats to have long hair, but if the goats that are bred are native to hot climates or in the wild have very short hair, then this would not happen in nature.
2. People breed cows to make lots of milk, without caring a lot about nutrients in the milk. In the wild, as long as the cow can produce enough milk for her calf, the cows with the most nutritious milk are more likely to have offspring that will survive. Also, holding a lot more milk in her udder inhibits the movement of the cow, which in nature would make it harder for her to survive.
3. People breed fruits, such as grapes and oranges, to have small seeds so that they are easier for people to eat. With natural selection, bigger seeds would be more successful in producing plants that survive.
4. Citrus fruits, such as oranges and lemons, often have to be shipped long distances, so they are bred for thicker peels to stay in good condition even through shipping. In nature, a balance was reached between thicker peels to protect the fruit and thinner peels so that the fruit is eaten (which is how it spreads its seeds). This balance is ignored by breeders.
5. Prickly plants that bear fruit or pretty flowers, such as raspberries, prickly pears, and roses, are often bred to have small or no thorns, so that they are easier for people to harvest or handle. The reason the thorns are there is so that the plant will not be disturbed. In nature, the plants would be selected for more, larger thorns, not fewer, smaller ones.
The thorns on this wild prickly pear cactus advertise, "don't touch me". However, because of the delicious fruits that this plant produces, thornless varieties have been created through breeding.
6. Pigs are bred for their meat. People breed them to be very, very, very fat, and in the process, other things that would be developed and selected for in nature, such as intelligence, are ignored, so they gradually diminish. When piglets are born they are usually separated from their mother and must nurse through a grate of metal bars.* Because of the massive size that has been bred into them, and the intellegance that has been lost, sows have been known to roll over on and crush their young. People say, "Wow, what stupid animals. It's a good thing that we humans came along to save those piglets. I wonder how they ever survived like that in the wild." They didn't. Evolution did not cause the pigs to be like that. The size and stupidity of domestic pigs would not have been selected for in nature.
These differences are caused by people having only one interest in mind: whatever they need the organisms for. So they get rid of traits that the organisms have or focus on only one thing, upsetting balances found in nature.
Breeding is important because it helps humans, but it is not always in the best interest of the individual organism or the species as a whole.
*Assuming they are allowed to stay with their mother at all.
Because of the massive size that has been bred into them, and the intellegance that has been lost through the breeding process, sows have been known to roll over on and crush their young.