Quote:
Originally Posted by questor
Moon, let me put it another way. How do you explain such diversity in fossil strata? If the animals in the layer were all exposed to a similar environment, why wouldn't they develop similar traits? Why would some eat meat and others grass? Why would some grow wings and others grow horns? Do their genes have some kind of signal mechanism that says.. I need wings, let's grow some?
|
Those are good questions questor.
The short answer is that different organisms occupy different ecological niches combined with the evolutionary processes of
natural selection,
genetic drift, and population isolation->
speciation.
Imagine this scenario from, say, 100 mya in Australia. A species of frog adapted to living in the rainforest undergoes a population explosion (perhaps because of many good years of rain or food, or an extinction of one of their top predators). Resources are always a limiting factor, so the frogs compete heavily for food, mating grounds, etc. Some frogs venture to the outskirts of the rainforest to take advantage of untapped resources (new food sources, etc.). Some of these frogs die because they cannot deal with the new environmental factors (new food sources, change in micro-climate, inadequate breeding grounds, etc.). But, some of these frogs survive due to a different genetic makeup/fitness that allows them to tolerate these new environmental conditions. These frogs reproduce and through time begin to adapt better to their new home. Fast forward 50 million years and analyze a frog from the center of the rainforest, and those on the edge. You might find that the frogs in the interior have retained much of their morphology and even genetics, whereas those frogs on the outskirts have changed their morphology/genetics to better adapt to their new environment. (they might have less webbing on their feet due to drier conditions, or maybe they adapted poisons to deal with the new predators, etc.)
This is a very simple thought experiment that is meant to illustrate how speciation occurs. When you figure in the complex web of life, it is easy to see how complicated it can get.
Also, it's important to realize that 50 million years is a *long* time. Scientists today can invoke adaptations in microorganisms in far less time than an average human lifetime. When you multiply this out to something like 50 million years, the possibilities become staggering.
Quote:
|
By the way, can you give an example of a succesful mutation that can be heritable?
|
I believe you are referring to
germ line mutations.
As MTM noted earlier in this thread, the vast majority of hereditary mutations are not beneficial. For a list of some beneficial mutations, check out the following link.
Examples of Beneficial Mutations and Natural Selection
