The article treats information arriving from the environment mainly under the heading of “learning”—for example, learning English vocabulary or learning to program—as though development first produces a nervous system and environmental input subsequently supplies it with acquired knowledge. But this seems to rely on a much stronger assumption: that, given the genomic program alone, a human zygote would unfold into something recognizably close to a normally wired human nervous system even in the absence of the appropriate external inputs. I am not convinced that this separation between “development” and “learning” is biologically justified.
My own case is one reason I find this distinction questionable. I have unilateral amblyopia caused by congenital anisometropia. Amblyopia is not primarily a defect of the eyeballs. It is a neurodevelopmental disorder in which chronically unequal visual input during a critical period leads to abnormal experience-dependent refinement of the visual system, particularly in visual cortex. Processes such as synaptic competition, strengthening, weakening, and pruning proceed under systematically distorted input and consequently produce maladaptive circuitry.
In ML terms, the problem is not that a fully developed visual system later fails to learn how to see. Rather, the developing system is being trained on the wrong input distribution, and the resulting model itself develops differently. The sensory data are therefore not merely “examples” presented to an already constructed learning machine; they are part of the process by which the learning machine is constructed in the first place.
More generally, I am not aware of evidence that a human embryo deprived of normal tactile, thermal, proprioceptive, vestibular, and other forms of sensory feedback—or systematically exposed to abnormal versions of them—would nevertheless develop an entirely normal nervous system. Many capacities that we casually describe as “innate” may therefore not be specified by the genome alone. They may instead be specified jointly by the genome and an evolutionarily expected environment.
If that is true, then the article's framing of the spatial complexity of nervous-system development as being bounded by the information content of the genome may be incomplete. The developing nervous system has access to an additional information source: signals from body and external world. Sensory input begins remarkably early, carries a great deal of information, and can have causal effects on the formation and refinement of neural circuitry itself.
Therefore neural development should involve two complementary processes. The article focuses primarily on decompression. But there is also a process running in the opposite direction: the developing organism continuously takes in a very large stream of structured environmental and bodily input and compresses regularities in that input into the organization of its neural circuitry. The information incorporated into the mature nervous system need not all have passed through the genome.
In that sense, the genome may not encode a complete developmental program so much as a program that is designed to operate under a particular distribution of environmental inputs. What we call “normal development” would then be a property not of the genome alone, but of the interaction between the genome and the environment that evolution could statistically “expect” the organism to encounter.
This is why I find the article's treatment somewhat too narrow. By placing environmental information largely in the later category of “learning,” it risks drawing too sharp a boundary between development and learning. In at least some neural systems, experience is not merely information written into an already developed network; it is one of the inputs to the developmental algorithm that builds the network.
I am only a bioinformatics undergraduate so my understandings of both bio and infomatics are somewhat slop. Would be grateful to see any criticisms.
TL;DR: I think that “the program must be small enough to fit in a genome” is incorrect. [Environment / external information / sensory input] whatever you call it is actually one part of “the program” and it's huge.