Quote of the Week
(October 29, 2024)

[Regarding cascades of gene expression, such as the sequential expression of the various genes that have been said to “determine” left-right asymmetry of the vertebrate body:] The normal expectation would be that if one blocks or changes the expression of earlier genes in the sequence, the disorder should accumulate and be magnified, perhaps explosively, in downstream gene expression, since proper cues for the later steps are missing. But

Surprisingly, this is not actually what occurs: each subsequent step has fewer errors than the previous step, suggesting that the classic linear pathway picture is importantly incomplete. Embryos recognize transcriptional deviations from the correct pattern and repair them over time … The existence of corrective pathways in embryogenesis and regeneration raises profound questions about the nearly ubiquitous stories our textbooks and “models” tell about the molecular explanations for specific events (Levin 2020).

All this may remind us of E. S. Russell’s remark that in biology “the end-state is more constant than the method of reaching it”. We also see here the principle that cell biologist Paul Weiss enunciated so clearly at mid-twentieth century, when he pointed out that the whole “is infinitely less variant from moment to moment than are the momentary activities of its parts”. At the lowest level of biological activity, molecules in the watery medium of a cell have degrees of freedom (possibilities of movement and interaction) that would spell utter chaos at higher levels if it were not for the fact that the lower-level activity is “disciplined” from above.

(from Chapter 10, “What Is the Problem of Form”, in Organisms and Their Evolution — Agency and Meaning in the Drama of Life)

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