gnostic
The Lost One
Evolution has been challenged and new discoveries were made, Senentia.
Darwin's theory on evolution was Natural Selection.
New discoveries have been found in the 20th century, but what were discovered didn't replace Natural Selection. Instead, each new discovery was either to complement Natural Selection, like with Mutation, or that other evolutionary mechanisms are possible, like Gene Flow, Genetic Hitchhiking or Genetic Drift.
Meaning that it is possible Natural Selection to occur and some places, while in another place in another situation, Gene Flow could happen.
Basically, evolution occurred by natural selection because some external forces encourage changes. These forces could be climate, the terrains, the availability or scarcity of certain types of food (in another change in diet), etc. and in order for the survival of future generations, they must learn to adapt to new changes. And these changes occurred at genetic levels.
Take the bears for instance. All the southern bears, like brown bears, black bears and grizzly bears, are different species or subspecies, but nevertheless they share many things in common. For instance, they all hibernate during the winter season, and they each have same diet. Although a large parts of their diets are protein, like fishes are other animals that they can catch, they also can eat fruits that they find (which make them omnivorous bears).
But what if we move some of these bears into the colder harsher Arctic region? Will they adapt and survive? Or will they maintain the same way of life as they did in the south?
The polar bears have learned to survive in the polar regions. Their bodies have changed, and passed down genes to generation of polar bears that best fit the colder terrain and different diets. They are actually related to the brown bears, but they don't hibernate and they don't eat any fruit, and their main diets are meats, like seals, but can eat fishes. Unlike their brown bear cousin, they can swim in icy open water.
The bear example is one of natural selection.
Another great example of natural selection, are the tortoises on Galápagos Islands.
One group of tortoises were the smaller tortoises with short necks and legs, and domed shells. These tortoises can easily find vegetation that are not high off the ground.
In a nearby island, the terrain was more barren, food harder to reach, so tortoises must find mates that had longer necks and legs, with different shape shells (known as the saddleback shells). The saddleback shells allowed the tortoises to stretch their legs and craned their necks upright to reach their food. In fact this she'll shape can even allow them to stand up on their hind legs.
Both tortoises are originally the same, but different conditions had changed the giant tortoises that they have become physically different to their smaller cousin species.
In another mechanism, like Gene Flow for examples, the changes occurred, not because of changes in terrains or climates or food sources, but because of different population of species have migrated into the region and breed with the native population, thereby producing mixed species. If the mixed species become the dominant species, then the two original species may either die out or become less populous than what they originally were.
Both natural selection and gene flow are possible, so the older theory (natural selection) haven't been replaced by the newer theory. Evolution now encompassed 5 different mechanisms.
I don't think we will ever replace natural selection, but it doesn't mean that new theories on other evolutionary mechanisms cannot be found...or the natural selection be updated. In fact, natural selection has already been updated, because of advancing technology and our knowledge on DNA.
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