If you start with the basis that Noah's ark: all species of animals came from a pair of animals or in some cases seven pairs, then you can use evolutionary theory to explain how we have such diversity in the world.
why we have so many different types of birds for example.
In only a few thousand years? Can you even fathom the number of species that exist today?
However, i disagree that we are becoming "better" or more complex.
I believe we are losing our genetic diversity and growing farther apart from each other and God's original plan.
That's not how evolution works. Speciation occurs when one group of species is divided and divided groups do not interbreed.
For example, if you read the OT and look at the life span of humans it decreased from the hundreds to what our lifespan in now.
If you study age and why people get old, you find that it is because we are not able to replicate our DNA accurately.
Can you prove this through scientific means?
I would propose that God made animals and they became separate species through lose of certain DNA strands which made them unable to reproduce with organisms who used to be of the same species.
Again, this isn't how DNA works. In fact, I'm not sure what you mean by "DNA strands". Are you referring to chromosomes? If so, understand that the number of chromosomes within a species doesn't actually matter. You can learn more here:
Basics: How can chromosome numbers change? – Pharyngula
List of organisms by chromosome count - Wikipedia, the free encyclopedia
Most mutations I've heard of cause cancer, not adaptions within organisms that would be naturally selected for survive.
Most mutations are very subtle and often unnoticeable with rare exceptions. Some mutations make plants and animals more prone to certain illnesses and others make them more immune.
Why were peppered moths ever in the textbooks as examples of evolution, when it was always known that the black and white genes existed from the start?
1. From the start of what?
2. The peppered moth experiment helps us understand natural selection.
3. You're confusing common alleles with mutations.
Mutations alter genes, and those genes are passed onto a parent's offspring. For a peppered moth, a mutation might make a moth's wings much darker than it normally would be without the mutation. The information for the darker colored wings wasn't initially there.
Of course, this isn't to be confused with junk DNA.
arrange ape and human skulls in a line, where the crossover is blurred.
When creationists say, "We've never seen one species transform into another species", these skulls serve as a wonderful example.
Futurama sums up the debate quite accurately.
[video=youtube;TTOla3TyfqQ]https://www.youtube.com/watch?v=TTOla3TyfqQ&feature=youtu.be&t=1m10s[/video]