Hashes don't need to have large changes in output for small changes in input. A hash just transforms input data into a fixed space. For example, perceptual has

Hashes don't need to have large changes in output for small changes in input. A hash just transforms input data into a fixed space. For example, perceptual hash functions like Locality Sensitive Hashing (LSH) for text and pHash for images are designed so that small changes in input produce small to no change in output. Also, your DNA is an order of magnitude (or more) more similar to someone in Tokyo than it is different to someone in Seattle.