If you've ever wondered why mice have been, and continue to be, science's favorite research tools it's becaus we are a lot a like. Yes, that little four legged furry bundle of whiskers and pink feet shares 99% of its genes with us. 75-80 million years ago that 99% was 100%. That was when our most recent common ancestor walked the earth. That ancestor split off into different directions. One lineage led to and the other led to mice.