When does life begin?

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.

 

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.

 

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.

 

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.

 

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)?

 

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.

 

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.

 

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?

 

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.

 

If "genetically distinct" designates personhood then many different cell lines (somatic ones) in your body that have acquired mutations throughout ones life are distinct persons.


To the OP:

Ryan has pretty much capped the thread, IMO. There isn't a hardline answer to the question of when a person becomes a person--And there never will be. Because becoming a person is a process. Its as silly as believing that turning 18 actually makes you an adult. In reality no such thing happens. Some people may mature very quickly and act like an adult very early in life, others maybe 30 and still not adults.That subjectively drawn hardline is done for the sake of social and legal purposes.

You can, as Ryan pointed out, pick many different aspects of biology to support when a person becomes a person--But all of these in the end will only weakly support that definition. Because it is a process, not an event. For instance you could take the approach of some specific milestone of neurological development. Or you could take the milestone of being able to survive outside the womb--Which again gets murky because of technological intervention. Without a NICU babies born before 24 weeks die, almost always. However, with the advent of technology at 24 weeks in high level triage centers something like 50% of babies will survive. So again, your back to ambiguity.

And any of those biological milestones all suffer the same downfall in the end: every fetus is different. No fetus is developing at exactly the same rate in exactly the same way. For example, at around 26 weeks brain waves begin to "look human"--But that doesn't mean that every fetus will reach this milestone on midnight of the 7th day of the 25th week. Or for example; reactive fetal heart tracings don't usually happen before 32 weeks, but again that isn't a hard and fast rule. I've seen fetuses at 24 weeks with reactive tracinings, conversely I've seen fetuses at 34 weeks who were non-reactive, delivered preterm for spontaneous rupture, had great apgars and were fine. Its statistics, not hard and fast rules.

 

Okay, let's. The biological issue is completely separate from the ethical issue, at least at first. However, there is more than one type of biologist. A paleontologist might look at the issue of humanity different from a psychologist. A geneticist may look at the problem differently from both.
As an amateur paleontologist, I prefer the cladastic definitions. In paleontology, an animal is considered one species throughout its entire development, from zygote to death by old age. A tadpole is still an amphibian and a frog, even though the tadpole vaguely looks like a fish.
One can not distinguish the species very well if one had only the zygote. This is a problem some paleontologists face when they have zygote fossils without any other stage. However, the paleontologist would simply look for later stages in the fossil record.
A psychologist studies the human mind. Of course, a zygote doesn't have a mind. So with regards to a psychologist, human life has to start after after the development of a brain. The psychologist may have difficulty distinguishing a human babies mind from a chimpanzees mind.
A geneticist defines the human species as a certain genome. Okay, when does an individual have a "complete" genetic set?
In some ways, the gametes have a complete genome even before fertilization. Sperms and ova have a full set of alleles. Yes, the zygote has double the chromosomes of the gamete. However, this is redundancy. Many genes are copied twice.
I could find you all sorts of biologists. Each biologist would define a different beginning to life. This is because the definition of life is operational abstraction. Biologists have to define life in terms of the tools they work with. There is no biological context separate from the instruments. The word life is relative, not absolute.
You asked what biology says. You claim not to be interested in the ethical question, just in the biological question. Here are three types of biologists. Psychologists, paleontologists, and geneticists. There are other types of biologist, but this is a good start.
Which type of biologist do you want to answer the question of when life starts?

 

Scientifically, no, as explained by the comments in this thread.

Politically, absoultely. Pick any definition you like and I guarantee you you can find someone who will swear to you that that particular definition is the ONLY correct one, subjectively speaking.


EDIT --- OOPS ... my dyslexia is showing again. Throughout the entirety of the statements above, the word "subjective" was translated by my feeble brain as "objective". that is, I THOUGHT they all said "objective"

 

It sounds like the answer you are looking for is that life begins at fertilization. Suppose we said that yes life begins at fertilization or no it doesn't. What difference would it make? If what somebody says about the beginning of life is different from what you believe, would it change your mind?

Does your question have anything to do with the issue of abortion and whether it should be prohibited? The answer is that it doesn't. The issue of whether abortion should be permitted is purely a political or legal one. If more people than not want abortion to be illegal, it will become illegal. So in the end the clergy or politicians can rant all they want on either side of the issue and all that matters is the law.