Eternity RPC Board
For the most part, ditto to Hadash's explanation. A species is roughly defined as the compatibility of gametes (sperm, eggs) and the ability to produce viable offspring. Going back a step, gamete production is controlled by genetic makeup (DNA, chromosomes) which codes for hormones that signal the gonads to produce gametes, so you can say a species is genetically defined. I say compatible gametes "roughly defines" a species because wolves and domestic dogs are arguably separate species but wolf-dog hybrids are a thing. I also say "roughly" because medical conditions or traumas causing interruptions to the normal physiology of a person's reproduction system (infertility), or any other animal's reproduction system, does not exclude them from being members of a species (although there again our definitions are dodgy considering we give a special name to mules, the product of a male donkey and a female horse, because they are innately infertile...).
The mutation question - "mutate" isn't really a term I like because, in nature, it's not as crazy as X-Men. Genetic disorders (cystic fibrosis, Down's, sickle-cell anemia, etc.) are all the result of genetic mutation, and we certainly consider a person with one of those to be human. But, in this case, I'm going to assume you're speaking of "bitten by a radioactive spider" or "fell into a vat of Chemical X", and in this case, I would say that your being human or not would vary on a case-by-case (mutation-by-mutation) basis as to whether or not you retained enough genetic sequences found in the human genome to still be considered part of our species. If your body became an amorphous, purple gel with sparkles inside of it, I kind of seriously doubt that your genes would be left intact enough to produce for you a human brain with all its former capabilities since it's rare that a single chromosome codes for a single part of your body (i.e. the part that turned you purple may have enlarged your prefrontal cortex; the part that gave you the sparkles deleted your medulla oblongata.) If, on the other hand, you just grew an extra toe, or had your hair color change, then yeah, sure, I don't think anyone would deny that you are still human. Essentially, if you can meet the rough definition for a "species", then yes, you are still part of that species.
In the case of a man with a prosthetic leg (or cybernetic limb if you want to approach it from a sci-fi vocabulary), he still has the genes which produce sperm which allow him to have viable offspring with a human woman. If he also lost his genitals in the accident that gave him the prosthetic leg, he at one time had sperm production abilities, and still has the genes producing hormones which signal the gonads to produce gametes - it's just that the hormones no longer have the appropriate receptors. Even if this man had never been able to reproduce with another human due to a medical condition like low sperm count or E.D., he is the offspring of humans, and innately biologically human.
A brain in a full-body prosthesis is still human based on the fact that the brain was at one point taken from a living human or was grown in a test tube from human-sourced materials with human genetics and was the product of two human gametes.The machine was never at any point human. We don't consider our cars to be extensions of our human bodies when we go for a long drive in a sense that we literally believe they become part of us (even despite how your buttcheeks mold to the bucket seats after a while, or how your thigh skin sticks to leather on a hot day), but rather vehicles. Disabled people in motorized wheelchairs don't consider the chairs to be literal extensions of their bodies and innately "themselves". I see a full-body prosthesis ("cyborg" scenario) in the same way; the human part (brain, foot, whatever) is the meat of a human, so it's a machine with human parts. Some people replace their car's gear shift with weird shit like a taxidermied deer hoof. While I wouldn't call the entire car a deer based on the hoof, I would still say the hoof contains deer genetics and came from an animal that belonged to the deer species, so it is a machine with deer parts. They're dead and not living like they may be in a cyborg, but it's the same regardless; define the meat, not the machine.
Now, certainly, there is a question of when to call it a "human with machine parts" versus a "machine with human parts". I suppose you can consider the importance of the brain in decision making, thought processing, emotions, desires, etc. The brain is probably needed to control the machine, so you may define that as "a human with a machine body". There is also the pure ratio, which I don't think is necessarily as important as type of human meats, but can be argued for. Is a being 20% human? 80%? What about half and half? I would say that this particular conundrum is related more to personhood than humanity considering the meaty parts are human meat regardless of what ratio or what type exist in/on the machine, which leads to the next topic...
Getting more to the side of androids (no human genetic material, but humanoid traits like emotions, personality, self-agency, thoughts, etc) rather than a cyborg or a human with prosthetic limbs, this is more a question of "what is a person" than "what is a human". "Person" and "personhood" have legal, moral, and philosophical implications. The easiest example of this is the debates surrounding abortion, of course; no one is denying that a human fetus is the result of human sperm and human egg cells, but rather the debate surrounds personhood.
Not covered in this discussion because nope, too sloppy, and I'm not a paleogeneticist: early homo genus "species" (Neanderthals, etc.) and whether a near 100% genetic similarity plus h. sapiens' ability to interbreed with them means they were all true "humans" and our modern binomial nomenclature system is whack, or whether your question was truly a lot harder to answer for our great^10 grandpops who had a thing for the apish lady next door.
TL;DR - Semantics. Human is a genetic/biological term and, although a little tricky when you get into the weeds, isn't impossible to define. Cyborg meat-machine ratio dilemma aside, you're thinking of personhood, which is definitely more difficult.
The mutation question - "mutate" isn't really a term I like because, in nature, it's not as crazy as X-Men. Genetic disorders (cystic fibrosis, Down's, sickle-cell anemia, etc.) are all the result of genetic mutation, and we certainly consider a person with one of those to be human. But, in this case, I'm going to assume you're speaking of "bitten by a radioactive spider" or "fell into a vat of Chemical X", and in this case, I would say that your being human or not would vary on a case-by-case (mutation-by-mutation) basis as to whether or not you retained enough genetic sequences found in the human genome to still be considered part of our species. If your body became an amorphous, purple gel with sparkles inside of it, I kind of seriously doubt that your genes would be left intact enough to produce for you a human brain with all its former capabilities since it's rare that a single chromosome codes for a single part of your body (i.e. the part that turned you purple may have enlarged your prefrontal cortex; the part that gave you the sparkles deleted your medulla oblongata.) If, on the other hand, you just grew an extra toe, or had your hair color change, then yeah, sure, I don't think anyone would deny that you are still human. Essentially, if you can meet the rough definition for a "species", then yes, you are still part of that species.
In the case of a man with a prosthetic leg (or cybernetic limb if you want to approach it from a sci-fi vocabulary), he still has the genes which produce sperm which allow him to have viable offspring with a human woman. If he also lost his genitals in the accident that gave him the prosthetic leg, he at one time had sperm production abilities, and still has the genes producing hormones which signal the gonads to produce gametes - it's just that the hormones no longer have the appropriate receptors. Even if this man had never been able to reproduce with another human due to a medical condition like low sperm count or E.D., he is the offspring of humans, and innately biologically human.
A brain in a full-body prosthesis is still human based on the fact that the brain was at one point taken from a living human or was grown in a test tube from human-sourced materials with human genetics and was the product of two human gametes.The machine was never at any point human. We don't consider our cars to be extensions of our human bodies when we go for a long drive in a sense that we literally believe they become part of us (even despite how your buttcheeks mold to the bucket seats after a while, or how your thigh skin sticks to leather on a hot day), but rather vehicles. Disabled people in motorized wheelchairs don't consider the chairs to be literal extensions of their bodies and innately "themselves". I see a full-body prosthesis ("cyborg" scenario) in the same way; the human part (brain, foot, whatever) is the meat of a human, so it's a machine with human parts. Some people replace their car's gear shift with weird shit like a taxidermied deer hoof. While I wouldn't call the entire car a deer based on the hoof, I would still say the hoof contains deer genetics and came from an animal that belonged to the deer species, so it is a machine with deer parts. They're dead and not living like they may be in a cyborg, but it's the same regardless; define the meat, not the machine.
Now, certainly, there is a question of when to call it a "human with machine parts" versus a "machine with human parts". I suppose you can consider the importance of the brain in decision making, thought processing, emotions, desires, etc. The brain is probably needed to control the machine, so you may define that as "a human with a machine body". There is also the pure ratio, which I don't think is necessarily as important as type of human meats, but can be argued for. Is a being 20% human? 80%? What about half and half? I would say that this particular conundrum is related more to personhood than humanity considering the meaty parts are human meat regardless of what ratio or what type exist in/on the machine, which leads to the next topic...
Getting more to the side of androids (no human genetic material, but humanoid traits like emotions, personality, self-agency, thoughts, etc) rather than a cyborg or a human with prosthetic limbs, this is more a question of "what is a person" than "what is a human". "Person" and "personhood" have legal, moral, and philosophical implications. The easiest example of this is the debates surrounding abortion, of course; no one is denying that a human fetus is the result of human sperm and human egg cells, but rather the debate surrounds personhood.
Not covered in this discussion because nope, too sloppy, and I'm not a paleogeneticist: early homo genus "species" (Neanderthals, etc.) and whether a near 100% genetic similarity plus h. sapiens' ability to interbreed with them means they were all true "humans" and our modern binomial nomenclature system is whack, or whether your question was truly a lot harder to answer for our great^10 grandpops who had a thing for the apish lady next door.
TL;DR - Semantics. Human is a genetic/biological term and, although a little tricky when you get into the weeds, isn't impossible to define. Cyborg meat-machine ratio dilemma aside, you're thinking of personhood, which is definitely more difficult.