When does life begin?

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What does science say?

Ryan_m_b

Neither of your options is correct. Life is a long chain reaching back to its origin. Consider: a zygote is formed from gametes, gametes are living cells that in turn arise from the living cells of an organism, all the living cells in that organism have a lineage that can be traced back to a zygote, a zygote is formed from gametes....

If you are trying to ask the broader question of when does a developing human become a conscious person (i.e. attain "personhood") then depending on how you wanted to define person the answer could range from 5 weeks after conception to years after birth for healthy individuals.

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Do you agree or disagree that a fertilized egg is a human life? If not human, then what species?

If not alive, then how to explain the biological processes that going on inside that we have always believed makes anyone or anything alive.
I think this was meant as a more philosophical one. Let's separate the biological issue and the philosophical/legal/social/women-rights one.

jackmell

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.

Ryan_m_b

It is a human cell and it is alive but that is also true of the gametes that make it.
As I stated all life can trace an unbroken lineage back to abiogenic beginnings.
That's not possible because the definition of life, human and personhood are not objective concepts. At best we can construct a sliding scale (e.g. animals are very alive, viruses are a little alive, chemical reactions in mycells are barely alive, a rock is not alive) but this is all to do with our subjective (albiet pragmatic) definitions.
The problem IMO is that statements like this are ripe for equivication fallacies. Sure the formation of the zygote is the point in which a genetically distinct organism is formed but is that really an "individual" in the social sense of the word? If so then all cells are individuals, if not we're back to the concept of personhood and when it comes into place, and IMO personhood is not something that rapidly arrives in an human but slowly develops with the span of that development crossing birth.

It's also not possible to seperate the legal and social connotations because a lot of our rhetoric is biased by these things. Classic example (and what is happening now) the idea that there is some sort of objective classification.

Gokul43201

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

jackmell

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.

Ryan_m_b

Agreed however I'd like to reiterate that as scientists we should be careful in using language that will mislead laymen by setting up an easy equivocation fallacy e.g. "scientists determine that fertilised eggs are individuals!" or to use another recent example "scientists find God particle (vatican yet to comment)"
True, but to explore the issue further would that not make IPSCs individuals (ignoring totipotency for a moment)?

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I need to narrow down my question to "human life."

I frequently heard comment that the "fetus is not human." It cannot be anything but human! Elephants have elephants, lilies have lillies, humans have humans!" If the child is born a human, it must have been a human the entire time in the womb.

Ryan_m_b

Here is the only scientific answer to your question:

- Human life didn't begin at a specific point but homo sapiens emerged as a seperate species about 200,000 years ago. Any human alive now can trace life back to that point (and beyond)

- Genetically distinct homo sapiens form at conception

- The term "human" can mean homo sapien or personhood. Biology can comment on the former and can weakly contribute to the discussion/debate on the latter but as it isn't an objective quality there is no way science can point and say "here it starts"

Lastly when a person says a fetus isn't human they aren't using the term in a taxonomy sense (i.e. they aren't denying it is biologically homo sapien) they are using it in a personhood sense.

jackmell

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.

Number Nine

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.

Ryan_m_b

Yes totipotency. Pluripotent cells can differentiate into any cell type with the exception of extraembryotic tissues. So for the sake of argument again, let's say we made a ITSC (inducible totipotent stem cell), would that be an individual?

onomatomanic

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.

jackmell

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.

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If we say at birth, then what is the difference between a child 5 minutes before birth versus one 5 minutes after? None, other than environment that child is in. "Personhood" should never be based solely on how you wanted to define it.

Is there any place for subjectivity in the beginning of life of an individual?

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There is no clear link between animals and humans, is there?