When does life begin?

Ambiguous question huh? As written I would have answered what, 3.5 billion years ago and even that can't be pinpointed to anything near a definite time. I think rather you mean when does the individual come into existence? In that case, I would argue at the moment of fertilization; as soon as the chromosomes meet, you're born.

 

Definitely chicken. Or dinosaur. It's definitely one of those two species.

 

Maybe not "social" sense, but just rather a genetially distinct organism. Also, I don't think you can equate the fertilized zygote to other cells in the body. For example, a liver cell can't (normally) change into a heart cell. The fertalized zygote is I think distinctly different than all the other cells in the body.

 

I don't think they can invoke the entire ontogenisis of an organism but rather are capable of expressing only a subset of the process. Something is missing in IPSCs that is present in the feterlized egg.

 

I agree, to an extent, but for the sake of argument: Is an acorn an oak tree? Is a maggot a fly? Is a tadpole a frog? I assume this is a disguised discussion on abortion, but I'll avoid expressing any political opinions in the biology forum except to say that the question of whether or not it is alive is irrelevant, since the cell is the fundamental unit of life, and thus every one of our cells is alive, including the gametes that went into making the zygote. There is no "beginning", only a fuzzy demarcation between stages.

 

I don't see that genetic distinctiveness has much to do with anything. That would imply that the offspring of some species which reproduce via parthenogenesis, or for the sake of argument a human clone, is somehow less alive than organisms with two genetic parents. In the former case, that implication is clearly absurd, and in the latter, it is at best moral quicksand.

One can certainly make a biologically-based argument as to when something is part of a parent organism and when it becomes a separate organism which the parent is merely incubating, but the relevant kind of separation in this respect is something other than genetic separation.

It seems to me, though, that a teleologically-based argument might be better suited to this question. What makes a fertilized egg special is similar to what makes the keystone of an arch special - not any physical difference, but the role is plays.

 

I'm not sure. Maybe I was wrong to suggest a fertalized egg was an individual. Not sure though when it becomes one otherwise. Surely a newly born baby is, so is a fully matured fetus just prior to being born. Maybe I can resort to the "ontogeny recaputulates phylogeny" argument and suggest when the embryology reaches hominid form, human individual is realized.

 

Necessarily, yes, because there's certainly no way to objectively define it. People, I'm convinced, don't really know what they mean when they ask "where does life begin?". They certainly never find the true answer satisfying (i.e. that the line, if it exists at all, is fuzzy because because they came from a fetus came from an embryo came from a zygote that was itself constructed from living components that were synthesized inside of a living creature which came from a fetus...).

Humans are members of the kingdom Animalia; we are, by definition, animals.

 

I don't think you're ever going to get a satisfactory answer when you keep asking loaded questions...

 

.....Seriously? Are you about to argue that humans did not evolve from prior non-human ancestors and that we share these ancestors with other extant species?

If that is the case, a science forum probably isn't the place for you.