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How can it be that babies are so routinely born perfectly formed?

  1. Sep 8, 2014 #1
    When I think about what a complicated piece of machinery the human body is, it seems there must be millions of potential ways for things to go wrong in the development of a baby. However, babies are typically born perfectly healthy, birth defects are rare, and this blows my mind a bit.

    Is it understood how this has become possible? I'm talking about an actual mechanism that ensures the DNA blueprint is so accurately followed. I mean, it takes us quite a bit of effort just to grow a uniform crystal in a lab, so when we're talking about the huge variety of different molecules that have all somehow got to take the shape of a normal baby... all those different types of cells in such precise configurations... there must be something interesting happening to make that all go smoothly?
    Last edited: Sep 8, 2014
  2. jcsd
  3. Sep 8, 2014 #2
    Of course, many of those millions of things that can go wrong will terminate the pregnancy before it is even noticed.
    Google "human embryo mortality" for articles.
  4. Sep 8, 2014 #3
    I've googled a bit and haven't found a number, but do I take that to mean that the majority, or even a decently-sized minority, of fertilised eggs come to nothing? Surely not?
  5. Sep 8, 2014 #4


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    You also might want to consider how difficult it is to produce offspring from certain animals in captivity, such as the larger creatures in a zoo, from artificial insemination or from natural mating procedures. I am not sure if it is rejection of the fertilized egg, inability to fertilize the egg, or other reasons, which you might be able to research to find out, but I mention this just to make you aware that there are pitfalls along the way for other animals as well. The difficulty with Giant Pandas comes to mind.
    Last edited: Sep 8, 2014
  6. Sep 9, 2014 #5


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    Perhaps this was the article you were searching for:


    The statistics here seem to add emphasis to the veracity of the term 'miracle of birth'.
  7. Sep 9, 2014 #6
    If you consider evoltion theory, the chance on a miscariage has been eliminated to a minimum. The organisms that would'nt be able to succesfully reproduce, would go extinct. This can also been seen as natural selection of ''good'' genes.
  8. Sep 9, 2014 #7


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    There are many processes going on during development, to answer your question would require a pretty comprehensive overview of developmental biology. I recommend purchasing a book on the subject. A good text book I've studied from is Principles of Development by Lewis Wolpert (a very prominent developmental biologist). If you're looking for something shorter and more accessible he's also written a book called A Very Short Introduction to Developmental Biology which written for non scientists.
  9. Sep 9, 2014 #8
    Wow, ok. That wiki page claims 15-20% of women who know they're pregnant miscarry. I never imagined it could be such a high number. Also:

    "around half of all fertilized eggs die and are lost (aborted) spontaneously, usually before the woman knows she is pregnant."

    Never would have guessed this either. So the reason that you can walk down the street on any given day and not expect to pass a dozen people with deformities is that those who start developing abnormally in the womb tend to quickly die, so as a general rule, you'll either make it out of the womb essentially perfectly formed, or not at all? This makes me think of Fallujah, with all their deformed babies from depleted uranium rounds or whatever else was used - they have a high percentage of babies being born very messed up, but is the total birth rate also much lower? Time for a google...

    Non-scientists, or just non-biologists? I'd like to have some grasp of how something as complex as a healthy human ever manages to turn out right.
    Last edited: Sep 9, 2014
  10. Sep 9, 2014 #9


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    You pose a good question -- it really is incredible, isn't it?

    But keep in mind not only that extremely high failure rate you mentioned, but also that there have been billions of trials (conceptions) to get to this point - and that's just for humans! There many, many more trials before that as we evolved from simpler organisms.

    It's a lot of trial-and-error, and there have been billions of trials.
  11. Sep 9, 2014 #10
    Indeed, whatever it is that safeguards development has clearly been honed to near perfection through many mistakes, but I get the impression that there's no bite-size answer here.
  12. Sep 11, 2014 #11


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    By the way, not all babies are born 100% perfection, if there is such a definition.
    And not all babies are born to term completion, but les than the 9 months mostly mentioned.

    You must have heard of the neo-natal ward in hospitals, surgery being done to three day old and the like infants ( to fix heart problems as one example ), cleft pallets, mongolism, feet turned inwards, blind, deaf, etc. , plus all the other physical deficiencies that show up in the years following the birth through to adulthood that are treated in children's ward of a hospital. The aspect that one can walk down the street and not see deformities speaks of either of certain deformities being treated in the early stages of development, certain types of deformity not outwardly being observable, certain types of deformities do not allow the individual to socialize as others do, and so on.

    One can look at eye sight, and just a small range of problems that can develop is something you DO see every day. Just witness the number of people who wear glasses or contacts to correct a deficiency of sight from the normal.
  13. Sep 11, 2014 #12


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    Why billions of trials?
    I do not really understand where that number comes from.
  14. Sep 11, 2014 #13
    Ah yes, this does make sense. I'm sitting here feeling lucky now because my body has always been essentially perfect in a functional sense. Never had any real health issues to speak of beyond the odd bout of flu, common chilhood illnesses like chickenpox, or an occasional broken bone. Do you have any percentage in mind for people like this?
  15. Sep 11, 2014 #14


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    Non-scientists. The short introduction series are, in my experience, very good at giving an overview. I'd suggest starting with that and then moving onto a text book.
  16. Sep 11, 2014 #15


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    This site says 1 out of 33 babies in the US has some sort of defect, which is surprising, to say the least. Honestly, I would have thought the rate would be much less, but I presume everything from mild to severe would be included in the statistic.

    I suppose more googling is is in order to find out the types

  17. Sep 11, 2014 #16


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    Let's see what Wiki says,

    They have a chart of defects of females/males which is interesting.
    they even say
    Never knew that happened.

    About radiation they say,
    All interesting stuff.
  18. Sep 12, 2014 #17
    Surely you wouldn't expect the physical mechanics to change from one birth to another......

    I am not sure of the actual process of DNA providing the instructions to produce a new "widget", but imagine this is a chemical process and is dependent on physical laws.
  19. Oct 25, 2014 #18
    I don't think that nature actually selects whether or not life lives or dies. Life is based on the effects of environment upon the cellular life itself. To say that nature selects those who live and dies is basically saying that natural selection is another for of an abortion or selecting the 'good' genes. Good genes only relate to a physiological sense of a sociological value of interpretation for ideological purposes. Determining how good genes are goes no further than how a person looks and is not a base for the cause of intelligence. Unless the person is under adult care for the entirety of their life which are really not considered good genes but such people still exist. Why is that? If such genes render a person to a state of being under adult care for the entirety of their life then nature should have selected them out of the process, naturally. But why do they still exist?
  20. Oct 26, 2014 #19
    Well. my sister lost an infant girl to a congenital heart problem, and my daughter had a friend whose baby son had to have a hemispherectomy.
    Big things like that are the exception, but I expect that small and undiagnosed misdevelopments are the norm. Just as boulders on the beach are less common than pebbles, which are less common than bits of gravel, which are less common than grains of sand.

    We're not all Olympic athletes and research scientists, you know.
  21. Oct 26, 2014 #20


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    You use the phrase "perfectly formed" but that's not the case. There's many forms that will work for one reason or another - different individuals have more robust systems in one way, but more sensitive and unstable systems in another way and these differences manifest in brain morphology, system connectivity, immune system differences.

    So how about "sufficiently formed"?
  22. Oct 26, 2014 #21


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    Natural selection has been working for a very, very long time... People who weren't able to reproduce properly simply couldn't transmit their genes to a non-extant progeny... Thus, people of present times have inherited a reasonably good set of genes, that enable they to survive and reproduce...
  23. Oct 29, 2014 #22
    The thread title and the comment shows many misunderstandings.

    The root of the problem is that there is no measure of "perfection" in evolution - evolution has no magic target.

    A shorthand is that evolution is "differential reproduction", meaning good enough is sufficient to make descendants for both the organisms and the (populations of) genes that are the actual objects of evolution.

    That results in the following:

    - The genome is not "a blueprint" that tells that this cell should look like this and goes there et cetera. It is a recipe that says a procreating organism will result if you "mix an egg into an environment with flour and sugar, and let it bake for sufficiently long".

    More specifically, a gene doesn't know anything else than how to act in an environment of other genes and a surrounding ecology in a way that will enable it to replicate yet another generation given a robust enough environment.

    Not that there isn't organisms that are much constrained. Some small organisms have an exact number of cells and their placement is pretty much given by development constraints. "Nematodes have a fixed, genetically determined number of cells, a phenomenon known as eutely." [ http://en.wikipedia.org/wiki/Caenorhabditis_elegans ] But that is not possible in the development of larger animals (or plants). Development is a mess, with migrating cells, induced cell death (to separate fingers, say) and all that.

    - There is an ecological difference between those organisms that put little effort into each egg and let the environment sort out the "not good enough" individuals, and those who make a few eggs and then have to care for them. Fish are examples or the former, humans of the latter.

    [These ecological strategies are called r/K selection after a model for it: "In ecology, r/K selection theory relates to the selection of combinations of traits in an organism that trade off between quantity and quality of offspring."; http://en.wikipedia.org/wiki/R/K_selection_theory ]

    So how do humans go from the apparently low quality of eggs to ensure good quality? Why, by pre-selection of course! That is why most sperms and eggs are wasted, until the mother can ensure that the fetus looks survivable. How that procedure is done varies and, I would guess, is less well understood. Sperm is competed though.
  24. Oct 29, 2014 #23
    lisa is referring to evolution. Every organism today has a lineage that has evolved for 4 billion years, and since the first 3.5 billion years were unicellular they have evolved pretty much at the same rate and with roughly the same amount of generations. A bacteria may procreate each day (20 minutes at fastest clip), so that is ~4*10^9*365 ~ 10^12 generations or a thousand billion or so trials at replication per lineage.

    You and your commensal bacteria is a proud result of a veeeery long experiment...
  25. Oct 29, 2014 #24


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    I am glad you replied. It's too bad that lisab didn't explain herself her logic.

    I wouldn't have gone that far back.
    Not even as far back as eukaryotes and meiosis , about 1.5 billion years ago, since we encounter unicellular organsims, and we are multicellular.

    Following the lineage, placentals arose around 100 million, with mammals originating somewhere in the Jurassic period.
    The most recent Hominidae arose about 20 million years ago.
    Home sapiens, about 100,00 year ago.

    There is also the Most Recent Common Ancestor, which may be only 4000 years ago.

    If we take just Homo sapiens, and a generation ocurring every 20 years, that would be only 5000 "experiments" that our species proper has done.
    Edit. If Homo sapiens experiments were not successful, or at least a percentage of them, the species would have died out long time ago.
  26. Oct 31, 2014 #25
    Well, it's really no more incredible than the fact you can unzip a 1 GB compressed movie file to watch the equivalent of 1000GB of pixels in exactly the same manner every time. The formation of a baby (or any other new organism) is a similar sort of a mechanical process where information is compressed in the form of DNA and de-compressed by little ribosome chemical factories.

    The process is seemingly error-free because over the course of 3.5 billion years, organisms who were not very good at making quality copies of themselves were crowded out by those who did.

    The key word in the above is "seemingly". Mammals have all sorts of biochemical fail-safes to prevent development of an embryo with defects. Those who did not were crowded out by those who did, because it is very expensive to carry to term a sub-par embryo. Thus, between 25 to 40% of human conceptions are naturally aborted by the body in the first weeks of pregnancy, the mother most often not even aware of what's happened.

    Of those embryos who survive to term, about 5% have visible malformations (in ~1%, the malformations are fatal or disabling). The number of "invisible" mutations is probably considerably higher. It's estimated that everyone inherits about 0.5 single-letter mutations in their parental DNA on average. So much for perfection...
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