Tuesday, January 29, 2013

When Cells Divide: the argument from uniqueness

MYTH: A zygote, formed during conception, is when a unique set of human DNA is created

FACT: This is FALSE. Just about every cell copy (mitosis) produces a 'unique' DNA variant (due to mutations, copy variations, duplications, transpositions, mitotic crossover, etc) and this is especially present during the production of gametes (spermatozoa and ovum) when DNA recombination shuffles the alleles between the different pairs of chromosomes (segments of DNA are sliced and randomized between the pairs of a chromosome).

Even 'identical twins', which are produced when the morula splits after the zygote has begun to divide into multiple cells, do not have IDENTICAL DNA - there are already differences in the copies at those early stages (both genetic and epigenetic differences).

So every gamete, while being haploid (having only one full set of our human DNA chromosomes, unlike our diploid cells which have 2 full copies), is a completely unique set of human DNA, unlike either of the originals but a complex mixture of the two. The Zygote is just the combination of these two, already unique, sets of chromosomes.


Genome-wide single-cell analysis of recombination activity and de novo mutation rates in human sperm
Cell Division
Genetic Recombination
Mitotic crossover
Scientific American: Identical Twins Genes are not Identical

MYTH: Life begins at conception / first breath

FACT: Life began only once (so far as we have evidence for) approximately 3.6 billion years ago - it is ridiculous to argue that it 'begins' at conception.

Furthermore, we know now that every cell in your body could be potentiated to become a new and unique 'human being', should we decide to do so.

And there are even **single-celled** humans (see HeLa), does each of those unique cells get full voting rights?

A human being is simply NOT a cell -- it is what a very large collection of specifically differentiated cells working together in concert create, and specifically there has to be a working human brain involved. This also applies to end of life, when there is no more brain function we recognize that we need to allow the body to cease functioning as well. The mere POTENTIAL to form a working human brain isn't sufficient or we would try to save every cell before death and potentiate it to be a full human being because it HAS that potential, so this is disproved reductio ad absurdum.

Also consider carefully that human beings seem to all have the POTENTIAL to do harmful things to other human beings. If the potential for something is the same as that something then should we preemptively incarcerate all human beings for their potential to do harm? Again, that would be absurd - reductio ad absurdum. You'd have to show why your 'potential' argument deserves special treatment or you're committing the Special Pleading fallacy.


Timeline of evolutionary history of life

MYTH: Gametes aren't 'alive'.

FACT: Then please explain how there can be 'dead' spermatozoa (see necrospermia) and why they don't create babies?

See Also:


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