At lizard-brain level we identify things as either "the same" or "the other."
We cast a jaundiced eye on "the other" as it might be a threat.
The trick is overcoming these instinctive intuitions and making a rational evaluation using scientific theory and proofs to substantiate the final decision, rather than only relying upon our basest instincts. (though base instincts have served us well and likewise should not be dismissed out of hand)
This is The Internet. Confirm for yourself anything you may see while visiting this strange and uncertain land.