What characteristics define a "human"?
Here are some questions to get you started:
If science one day manages to copy an entire human's brain into a computer such that the all their memories, the way that person thinks, behaves, etc. are exactly the same as the original "copy", would you consider that computer human?
If you amputate all of a human being's limbs, are they still human?
If you cut off a human's ears, eyes, nose, tongue, etc., are they still human?
If a human's mind goes into a vegetative state, are they still human?
Does a single human cell with fully in-tact genuine human DNA constitute a human? (ex. a skin cell, a recently-fertilised egg, etc.)
Are recently-deceased humans still human? Will they always be human or is there a point in time when they are no longer considered human?
Are there fractional humans? (ex. measured by number of limbs, one's degree of intelligence, ability to think critically, amount of worldly knowledge, etc.)