Having watched Steve Fuller I see that there are a lot of ways you can categorise a human. So here I am trying to elaborate what I think it is to be human
Functional – A human is a tool creating, social/collaborative, being with linguistic capabilities.
Which is good as far as it goes but is not specific enough, there are a number of other species on this planet (most notably the Great Apes) that fit that definition and there may well be species on other planets that also fit.
So biological – a human being is something that has some % of DNA in common with (which human do we choose?) and is able to breed with other humans. This is again problematic choose too low a % and we are including other species that some might be uncomfortable calling human, too high a % and we might rule out some current groups or some human descendants in a number of generations. There are other problems with the biological but I will come back to those.
Cultural – a human is someone who is part of a community of other human beings (and has been raised in a human community?). Is what makes us human other people?
I like the cultural definition, it appeals to me that it is by our daily interactions with others that we define what is and what is not acceptable “Human” behaviour, and it ties into a pet theory of mine that the reason why some of the rich and famous go a bit “unusual” is that they don’t have the normal checks on their behaviour, when you are really powerful, people tend to not to say “No you are wrong, thats stupid” even when what you are saying is really stupid.
However the cultural one again could be problematic – if an alien crashed to earth and was raised by humans (Superman!) does that make him a human? If we do create AI they will have been raised in a human culture so are they also human?
Hopping back to the biological definition – it is likely to be problematic in the future due to 2 changes, we will be able to alter the DNA of our descendants and we might reach a stage where people that were once human have replaced so much that they are mainly machine (read bi-centennial man) or have uploaded completely.
In conclusion – I would like to make the case that anything that can meet the Functional and Cultural requirements should be considered a human being. I am aware that there are some “Humans” that might be uncomfortable with such a wide definition of Human, however I have always been an inclusive type of being and would be proud to shake the hand/grasping mechanism/flipper/pseudopod of those that would call themselves human.