Exploratory Growth

Bone formation leads. Nerves, muscles, and blood vessels explore randomly and stabilize near the skeleton. Mutate the skeleton and the soft tissue adapts automatically — no separate mutations needed. This is Kirschner's "facilitated variation" made visible.

"Bone formation is the leading event. But everything else is exploratory and adaptive... it's not that it has to be told what to do; it finds its path by variation and selection. The nerves grow out randomly until one hits the target, and that stabilizes that nerve. It looks like the nerve knew where to go... it's just stabilized. In the same way, flies don't fly toward flypaper; they just get stuck there."
— Marc Kirschner, Harvard lecture on Evolvability

Skeleton (deterministic) Nerves (exploratory, stabilized) Vessels (exploratory, stabilized) Muscle (exploratory, stabilized)

How it works: The skeleton is drawn deterministically using the normal biomorph algorithm. Then three tissue systems — nerves, vessels, and muscle — grow from random seed points. Each tissue branch extends in a random direction, but is stabilized (kept) only if it stays close to the skeleton. Branches that wander too far are pruned. The result: soft tissue that hugs the skeleton's shape, whatever that shape is. Mutate the skeleton and the tissue re-adapts automatically. The density, reach, and branchiness genes control the tissue's exploratory behavior — not its exact form. A seeded RNG ensures identical soft tissue for the same genotype.