Sorry Luke,
I got on a soap box and didn't take your age into consideration.
Let me say it this way.
People believe all sorts of things.
When several people get together and try to work together there are some beliefs they will need to agree on because the belief is a necessary part of the work and there are some things on which they can agree to disagree.
Now where disagreements about "what is true" come up how can the group reach consensus? How do they decide what to accept as true? This is the branch of philosophy called
Epistemology.
There are various Epistemological disciplines a group can choose.
They can elect a leader or the biggest toughest guy can slug it out and become the leader, however the leader is elected... when everyone accepts the leader's decision as to what is true then this is the epistemology of
authority. The authority needn't be a living person but can be the
author of an authoritative text.
Another form of epistemology is
faith. Typically faith is a personal epistemology and cannot be used to build a consensus between random people. Rather people with a common faith will group together on such endeavors as their faith dictates (which is sometimes to try an annihilate those with different faiths when that is the moral choice dictated by their faith based belief).
Science is an epistemological discipline of repeatable empirical testing. In the issue of say how much support a building needs to withstand a hurricane, you can test the strength of building materials... and I mean literally "you" can if you don't trust what others tell you. You can measure the maximum wind speeds of hurricanes, you can calculate the forces acting on a building and you can come to a conclusion about how likely is it a building will be damaged.
But part of the strength of science is it only addresses issues which
can be tested or which can be derived from testable hypotheses.
One testable fact is the rate at which
mitochondrial DNA (mDNA) randomly mutates. (Mitochondrial DNA is the DNA outside the nucleus of the cell which is passed on only from the mother.) Siblings have almost exactly the same mDNA as their mother and their mother's mother, but for random mutations induced by background radiation, toxins, viral infection, copy errors during cell division, and other methods. You don't even need to know the exact mechanisms but simply measure the rate of change looking at the mDNA over many generations.
With that information you can compare the mDNA of two people and extrapolate how far back along the two persons have a common maternal ancestor. You can do the same for three or more people and in general calculate roughly how far back a given population would have to have descended from some smaller population size.
Figuring 6000 years is only 300 generations it is not very likely in the extreme that we evolved from a small population that recently. Remember that this mDNA doesn't get shuffled around during reproduction but is inherited totally from the mother. To genetically engineer the human race 6000 years ago would have required hundreds of thousands of separate individual genetic engineerings on hundreds of thousands of pre-humans who had previously evolved over millions of years. It just isn't a reasonable hypothesis. They wouldn't have had any reason to work on so broad a scale except to hid this bit of evidence I am suggesting here.
It must even go further than this as we do have good correspondence between mDNA drifts and various pre-historic migrations of humans.
http://www.dnai.org/text/mediashowcase/index2.html?id=250"
In fact one of the best bits of evidence I can imagine that we were genetically engineered recently would be that the mDNA evidence points to a common female ancestor to all humans some 300 generations ago.
Finally let me say that another scientific fact you can empirically confirm is that people tend to seek evidence which preserves their given beliefs rather than choose their beliefs based on evidence. Indeed it is a difficult phenomenon to excise from scientific investigations and careful discipline in the methods must be exercised to prevent bias. Consider the Pons and Fleishman debacle.
Take this and consider the "evidence" presented by those advocating this 6000 year ago external intervention. Look at their motivation and the scope of the evidence they consider. Is it a single argument made from a single phenomenon? If so then they are likely rationalizing a previously held belief rather than taking the evidence and drawing the most likely conclusion.
