One of my favourite, explained pretty well by therationalizer.
I'd like to suggest that we both present what we feel is the strongest argument. This way if our strongest argument is debunked then there is no point in bringing up another argument on account that it would be weaker.
So, I shall start.
1: Evolution is an observed fact - google it.
2: Evolution through natural selection is the scientific theory that says how natural selection guides the fact of evolution to create different (but similar) species.
The evidence I feel is strongest for evolution through natural selection (hereinafter written as "evolution+ns") is that of endogenous retroviruses.
A retro virus invades a cell. It then snips the DNA within the cell and inserts a copy of its own DNA. When the cell is replicated its DNA is processed in order to create the relevant proteins, during this process the RV's DNA is processed and a copy of the RV made which then goes off and invades another cell. This means that the DNA copy within that cell is permanently altered. Each cell of our bodies contains a copy of our entire DNA. The DNA within the single cell is altered, not our entire DNA.
If the invaded cell is either an egg or a sperm then the life which results from a fertilisation of that egg or sperm will have their entire DNA based on the DNA with the RV DNA insertion. Once the RV is passed on via DNA it becomes an endogenous retro virus (ERV.) An RV inserts itself at a random place within the genome. The human genome is approximately 3.4 billion in length. Seeing two people with the same virus injected into the same part of their DNA shows that they inherited that DNA mutation from a common ancestor.
When we examine the human genome and the genome of chimps (which have a DNA length of approx 3 billion base pairs) we see that there are 7 instances of ERVs in common with humans. Not only are these the same virus in each case but they are also in exactly the same location within the genome. The chances of two independent creatures (with a shortest genome of 3 billion base pairs) getting the same infection at the same place 7 times is 1 in (3 billion to the power of 7.)
Then you have to factor in how many different RVs could have infected this location and account for the fact that in each of these 7 instances it is the same RV.
Also, based on the length of a DNA and the average number of mutations observed per generation + the average life expectancy of the species it is possible to count the number of mutations within the virus DNA and get an approximate period of time at which the infection took place. In each of the 7 instances the number of mutations corroborated that the infection took place at the same time in both chimps and humans.
So, the probability of 2 different species getting infected in the same place is
1 in 0.2187E+67 (2187 with 63 zeros after it)
Which alone is a fantastically small probability. Then factor in it being the same virus AND going endogenous AND happening at the same time and you end up with a number so unbelievably small that it just isn't going to happen.
But that's not all!
Not only are there 7 in common with chimps there are a number of ERVs which (chimps + humans) share with Apes. Showing that a common ancestor with an ERV DNA mutation split into two species, which would later become Apes and the ancestor of Humans/Chimps. In fact if we look at the genomes of the various species on Earth today we observe this ERV phenomenon all over the place.
ERV in mammals also seen in
Apes, which have additional ERVs also seen in
Chimps, which have additional ERVs also seen in
Humans
It's the same for species of birds and reptiles too, with some ERVs being present in all reptiles for example, and then additional ones existing only in more closely related species of reptile. The same in other mammals too, where cats will share the same ERVs as other mammals but not the same ones as Apes, but more amongst the various cat species.
In short, the ERV observations corroborate the evolutionary tree of life (humans + chimps from a common ancestor, that ancestor from a common ancestor with apes.........from a common ancestor of mammals.)
As you can see the evidence from ERVs in humans/chimps alone is incredible. Then add in all the other species and it is fantastically incredible. Also take into account that this is not DNA that was "put in from the start as part of some clever design" these are viral infections which mutated the species' DNA at various points after life had started.
How do we know these are retroviruses?
DNA is made of the nucleotides A,T,G, and C. The other side of the helix is predictable because they always pair up like so
A to T
G to C
(and complimentary to above)
T to A
C to G
So let's take some imaginary DNA
ATG CAT GCA TGC AAA ATG CAT GCA TGC
TAC GTA CGT ACG TTT TAC GTA CGT ACG
One side of the helix is at the top, the other complimentary side is beneath it. I have separated them into 3's to make it easier to read.
When an RV cuts the host DNA is does not cut a straight line, what it does is to cut one side of the helix at position X, and the opposite side at X+Y. So in a case where Y=3 what you'd get after a cut is this
ATG CAT GCA TGC AAA
snip ATG CAT GCA TGC
TAC GTA CGT ACG
snip TTT TAC GTA CGT ACG
And then with the RV's DNA inserted...
ATG CAT GCA TGC AAA --- --- --- --- ---
ATG CAT GCA TGC
TAC GTA CGT ACG
--- --- --- --- --- TTT TAC GTA CGT ACG
The "
" denotes a gap in one side of the helix due to the cut and "---" the virus DNA. The virus then inserts its own DNA at the staggered cut position. Now when the body processes this DNA to duplicate the cell look what happens. The
gaps in the DNA are filled in by the body with their complimentary nucleotide
In the top cut position the TTT below is complimented by AAA at the top.
In the bottom cut position the AAA above is complimented by TTT at the bottom.
(Note that I only used AAA TTT to make it easier to spot, the RV injects its DNA at a random place and could therefore work on any combination of ATGC.)
So you see we end up with a duplicate sequence of 3 nucleotides. If I exclude the virus DNA from the pattern you will see this
Before
ATG CAT GCA TGC AAA ATG CAT GCA TGC
TAC GTA CGT ACG TTT TAC GTA CGT ACG
After
ATG CAT GCA TGC
AAA AAA ATG CAT GCA TGC
TAC GTA CGT ACG
TTT TTT TAC GTA CGT ACG
Note the duplicate AAA and complementary TTT.
So to identify an ERV we first look for duplicate base pairs and then compare the DNA between them with the DNA of known retroviruses.
So we know
1: The mutation is due to an RV infection.
2: The mutation went endogenous.
3: Approximately when the RV went endogenous.
4: The mutation was passed onto descendants.
5: The descendants diverged into separate and distinct species.
So either all species evolved from other ancestor species (including humans) or a divine creator first created all life, reused DNA patterns (because they worked?), and then for some unknown reason came back multiple times over a span of millions of years and altered the DNA of groups of species with retro virus DNA at the same time in order to make it look as though they had all inherited an ERV DNA mutation from a common ancestor.
Topic: FreeSoul007 vs Prince Spinoza: theory of evolution