alt Hacker News> 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?
An example of the contrary:
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.