> Morphology is determined by the combination of genes, chemical signals, original cell machinery, and apparently electrical signals. But we never believed that genes determined morphology alone, eg, we know that chemical signals can cause anomalies.
For the consistent parts - eyes may be different colors but are overwhelmingly consistent - what else could be the ultimate cause but DNA? For example, if those chemical signals, cell machinary, and electrical signals produce the same results billions of times over 200,000 years, then they must function the same overall. How does that happen if the chemical signals, cell machinary, and electrical signals aren't determined, even if indirectly, by DNA?
Your eyes would be misplaced if the process from cell clump to mat to tubule failed due to chemical signaling failure, but the whole embryo tends to be spontaneously aborted when gestation fails so catastrophically.
And despite genitalia being roughly one of two forms and similarly positioned, chemical signals can disrupt their formation.
> How does that happen if the chemical signals, cell machinary, and electrical signals aren't determined, even if indirectly, by DNA?
They don’t produce the same results with perfect accuracy — 75% of pregnancies are spontaneously aborted, at least in part due to developmental failures.
But the problem with this argument is simple: you have a human cell everywhere you have human DNA, so those correlations with DNA are also correlations with cellular machinery and with particular chemical signals from the mother. There was no point in those 200,000 years where DNA operated independently of those other mechanisms — we can only say the system as a whole reliably creates those features.
Interesting points, especially about the challenge of correlation. I guess we could remove DNA and see what happens ...
Somehow the machinary is passed down: Do we know of another mechanism besides DNA that is self-perpetuating? Is there any living creature without it? Prokaryotes (bacteria) even have DNA.
Or is there a way to do it without self-perpetuating mechanisms? Is that logically possible? Some machinary might be perpetuated by other machinary, e.g. the chemical might recreate the electrical, meaning it's not self-perpetuating. But that's not different than DNA: DNA itself isn't the machinary, but its self-perpetuation is what recreates other parts.
I suppose some parts of the environment are consistent, such as sunlight, air, water, and heat, but the environmental stimuli must trigger something that is already there.
> I guess we could remove DNA and see what happens ...
If I have a stool with three legs, and remove one leg causing it to fall, can I conclude that removed leg is what made it stand?
You’re making the same mistake as before in reverse: DNA would do nothing without a host cell or chemical signals, either.
> Somehow the machinary is passed down: Do we know of another mechanism besides DNA that is self-perpetuating?
The system as a whole is self-perpetuating, but DNA is not self-perpetuating: without a host cell and without ambient chemical signals, it cannot propagate. That’s in contrast to ribozymes which can be self-catalyzing RNA, ie, truly self-propagating chemicals.
In the RNA world hypothesis, such self-catalyzation was the origin of life; and by the time DNA evolved, it did so within a running biological system and as merely one component of cellular replication.
As a whole the system of chemical signals, DNA, and cellular machinery propagates; but just like our stool example, removing any of the factors causes that to fail.
The DNA removal comment was as joke; sorry if that wasn't clear.
No system is self-perpetuating, per the Second Law; all need other inputs. What makes the machinary yield the ~same results ~every time is DNA.
> In the RNA world hypothesis, such self-catalyzation was the origin of life; and by the time DNA evolved, it did so within a running biological system and as merely one component of cellular replication.
Is there evidence of that? Afaik the earliest evidence is prokaryotes ~~3.5 billion years ago, and prokaryotes generally have DNA.
For the consistent parts - eyes may be different colors but are overwhelmingly consistent - what else could be the ultimate cause but DNA? For example, if those chemical signals, cell machinary, and electrical signals produce the same results billions of times over 200,000 years, then they must function the same overall. How does that happen if the chemical signals, cell machinary, and electrical signals aren't determined, even if indirectly, by DNA?