What do you mean big radiation? Is this a supposed event?
It is a blanket term for a large number of evolutionary events. It is the same as "diversification" of something (lets say invertebrate multicellular organisms). In the Precambrian there were only a few sponges and other odd worm-like things. By the end of the Cambrian, most every class of invertebrates that ever has existed was found in the fossil record (class as in kingdom/phylum/
class/order/family/genus/species), with the possible exception of some arthropod classes. So radiation is a major divergence from just a few sorts of critters into a large variety of them.
Where you do not say that fossils exist⦠then it is the basis human imagination?
Imagination would be the wrong word. Actually, if there were no fossils or fossil record
at all, we would still have high confidence in the theory of evolution from the major lines of evidence that it is very successful in predicting, and which come in the areas of comparative anatomy, biogeography, and the all important genetic data. Fossilisation is a rare event. We know that we don't know what most of the creatures that have lived on the earth have looked like. When we do find transitional fossils, it helps us understand the details of how this character or that trait evolved, and it gives us more insight into how ancient creatures lived, but it isn't the prime evidence for evolution.
On the other hand, if the fossil record was all we had to go on, and the other lines of evidence didn't exist, scientists wouldn't be unanimously accepting the Modern Synthesis of evolution - if they accepted any evolutionary theory at all. I point this out to try to show you the relative importance of the fossil record in our understanding of evolution. The transitions and trends we find in the fossil record are just the "icing on the cake" for evolution. (later you might be interested in seeing a review of some of the most important evidence here:
http://www.talkorigins.org/faqs/comdesc/ )
The evidence from the other areas is strong and conclusive, and the transitional fossils we have agree. So, the only thing left to the human imagination is
what the transitional forms that didn't fossilize looked like.. When new transitionals are found the hypotheses of scientists about what those forms looked like get a chance to be tested.
How do these changes occur?
Very simply put, through descent with modification.
A better answer is a list of mechanisms that cause evolution:
Genetic mutation ("random" changes in the DNA of an individual, which may be expressed in traits that reduce the individual's chance of reproducing, increase the individual's chance of reproducing, or do neither. They are essentially random in nature, because we cannot predict what mutation will happen next. A better word is chaotic. A thunderstorm isn't a random event - it has definite causes, but it is chaotic - when one will occur looks random to us.)
Lateral gene transfer (transfer of DNA directly from one organism to another. This normally happens only in single-celled organisms)
Recombination (exchange of DNA between individuals within a breeding population during sexual reproduction)
All of those act on individuals within a population. The next part of the list are mechanisms that act on the population at large, to change its overall genetic makeup:
Gene flow (individuals with different make-up moving into or out of a breeding population.)
Genetic drift (random change in "allele frequencey" - the number of one kind of gene in the population - owing to essentially random factors)
Any of a number of selective pressures (most importantly "natural selection" for reproductive fitness, changes in a population's over all genetic makeup due to differences in a gene's impact on the organism's ability to survive and reproduce).
That about sums them up.
How do these changes occur?
This is covered above...
What alters the DNA to produce these different species?
The same processes that change the genetics within a population or species are responsible for the separation into two species when two populations of the same species stop mating together for a long time for any reason.
When the animal becomes more complicated does not the DNA also become more complicated?
In general, the reverse is true. That is, when the gene sequences take on more variety (including more complexity), the organism that carries those genes is likely to become more complex.
How can evolution, on its own, add to the complexity of the creature?
Very small steps, very long periods of time. All of the same mechanisms I listed for you above. That is a "graduate student" level question, and beyond my powers to answer to your satisfaction. I must refer you to here:
http://www.talkorigins.org/faqs/fitness/
So tell me their secret! How can I alone add to the complexity of my DNA?
Only through genetic engineering. That isn't a part of evolution (well, it isn't yet anyway). And genetic engineering isn't any match for 3 billion years of engineering by natural selection...
I cannot understand how something of such a simple nature is not seen by those who work demands that they know the complications of creation. Do you think maybe they have become lost in the forrest and can not see the light to find their way out?
