* all the structures grow from a single cell
* somehow it's all encoded in DNA (only 6 billion bits in humans, which has to also build cells and their ultracomplex machinery)
* this all had to evolve using only a very noisy objective function
This makes me think that we need far more than just 6 billion bits to actually encode the entire process of new life formation (each instance always piggy-backs off the previous, and always provides processes/information).
(There is a contrarian theory that says that the cell membrane does not exist at all, look up Gilbert Ling. So it's no surprise that things can move in and out of the cell under certain conditions.)
Someone should write a short story about that.
The claim is biological, not sociological.
Or, more accurately, it's like having binary machine code for an unknown ISA with no information about the CPU, and no example CPU.
Also, even if we accepted that DNA fully specifies how a cell can create an identical copy of the cell that contains it, that doesn't mean that it specifies how to create a cell from scratch. The "instructions" in DNA could very well depend critically on details of the current cell. For example, the DNA could specify se thing like "take 1% of the substance secreted in organelle A and mix it with 90% water and 9% the substance secreted by organelle B". This instruction is perfectly good for specifying a copy of the current cell, and perfectly useless if you don't have the original cell for which it is meant.
This sort of thing could very well apply at the level of the whole fetus. Details of the uterus and other parts of the mother organism may well be critical parts of the "program" described by the DNA. For example, it's easy to imagine that the early fetus follows instructions like "let this much fluid pass through the umbilical chord", or "grow horizontally until you find this much pH difference between the extremeties" or whatever other instructions that are only useful in the context of an existing functioning mother organism.
And even beyond the individual, you would have a big problem recreating the species to allow for a second generation to exist at all. In particular, even if you had a whole living healthy female mammal, you would have no information at all for how to create a male of the species, so no way to create sperm cells, so no way to perpetuate the species. So the DNA of a female mammal doesn't contain information for how to make more of the species. And if all you had was a male organism, you would lack the information probably encoded in the living female that I was discussing earlier.
As a side note, this problem would not exist for birds, where the female bird does have both male and female DNA.
What we don't know is what that function is. Put differently, what is the question?
It's called maternal effect (https://en.wikipedia.org/wiki/Maternal_effect)
He is studying exactly this. He found that when developing, cells move and grow in a particular direction. But when an obstacle is placed in their way, they move around it to somehow still end up where they’re supposed to.
DNA is not all of the encoding. Even cells appear to have some form of navigation or space search capabilities.
In addition to those unavoidable ones, there can also be things going wrong by accident (e.g. the pregnant woman suffer physical injury which kills the fetus).
for example (pre)eclampsia. we still don't know WTF is going on exactly (but it's basically abnormal blood vessel formation between the fetus and the uterus), and a few decades ago it was basically guaranteed loss of the fetus or the mother (or both), in about half a percent of pregnancies.
nowadays thanks to medical science it's a hundred-times more manageable.
It's unclear how much those non-genomic components affect organismal phenotypes; presumably, there is some minimal collection of factors that would suffice to allow us to construct an artificial egg cell that is viable for reproduction.
Couldn't this be proven by growing mammals in petri dishes?
If the entire information is encoded in DNA, then the fetus would grow fine.
If however, the fetus needs to be in a womb to develop, then there must be information (and resources) that need to be sent from the mother to the baby in a sort of quine fashion.
Consider a Java compiler or python interpreter, they are themselves written in the target language, unless we are talking about early version. So you already need a java compiler to compile Java, the code for the compiler does not hold all of the necessary information, as you need a mother compiler to execute it.
Which part of the target is in the code and which in the interpreter/compiler?
A thought experiment would be a language where a built in statement compile() compiles code according to specifications. Thus the code for a compiler would simply be compile().
My best guess is that fetuses can only grow inside a functioning human, and that the information in DNA is not sufficient, you need a functioning specimen to grow another specimen.
A 27-state two value Busy Beaver can implement "Give a counter-example to Goldbach's Conjecture" - if there are none the program never halts. We can recognise that, and say "Oh dear" but it gets us no closer to an answer. Six billion isn't even in the right ballpark, our ability to understand the meaning of every self-acting machine extends maybe to six or seven bits if we're very smart.
One has to be cautious to not assume that the only data DNA holds is in base pairs.
We know that secondary factors like inter- and intra-strand interactions or DNA-histone interaction encodes information as well.
A good analogy is a book. While it is made up of individual letters, the combinations build to words, which build to sentences, which build to ideas, which can interact with other ideas (sometimes in other chapters!) to create a complexity beyond just the combination of letters would suggest.
That's not even getting into the temporal aspects of DNA expression.
> only 6 billion bits in humans
It’s probably not far off being easier to read DNA than a CD. And it’s surely less frustrating.
~750 megabytes (unit conversion via google)
Two cells: Egg and sperm