Flexible Niches: Viking Trade/Raid Duality and Behavioral Plasticity

The Advantage of Being Undecided

In the Galapagos, I observed finches with beaks shaped for particular seeds. Large beaks crack hard shells efficiently. Small beaks pluck insects from bark crevices. Specialization confers immediate advantage when resources remain stable. Yet the climate shifts, drought arrives, and the specialist who thrived yesterday starves today. The generalist, less perfectly adapted to any single food source, survives by switching diets.

Vikings demonstrated a peculiar form of behavioral plasticity that puzzles those who expect societies to commit to single niches. The same individuals who traded peacefully at river markets one season raided coastal monasteries the next, or hired themselves as mercenaries to Byzantine emperors. This was not confusion but strategy. Historical records, written by victims, emphasize the violent minority and create the illusion of pure predators. Yet most Viking contact with Europe was commercial rather than martial. They assessed conditions and selected roles opportunistically, just as a bear choosing between salmon runs and berry patches follows gradients of caloric return.

Borderland Flexibility and Specialist Collapse

The borderland position itself creates selection pressure for versatility. Empires possess mass, hierarchical organization, and strategic depth. They absorb losses, field standing armies, and optimize for stability. Vikings lacked population reserves and bureaucratic infrastructure but compensated with energy, openness, and rapid adaptation. Small societies cannot afford rigid specialization when survival depends on exploiting momentary weaknesses in larger neighbors.

Consider the pizzly bear, hybrid offspring of polar and grizzly parents. Polar bears evolved skulls and dentition exquisitely adapted for blubber consumption on sea ice. Climate change removed that substrate. Specialized morphology became a liability. Grizzlies, by contrast, consume insects, plants, roots, berries, rodents, fish, and carrion with equal facility. The pizzly inherits this dietary flexibility and thrives where pure polar bears decline. The parallel to Viking versatility is instructive: when environments fluctuate, the capacity to switch modes outweighs efficiency in any single mode.

The slave trade reveals how Vikings connected their multiple roles into an integrated system. Raids produced captives. Trade networks exchanged those captives for silver in Byzantine and Abbasid markets, where religious prohibitions against enslaving coreligionists created demand for pagan victims. Mercenary service built relationships that facilitated commerce. Each activity supported the others, creating a behavioral repertoire rather than a fixed occupation.

Overparameterization and the Adjacent Possible

Recent work in neural network training reveals an unexpected pattern that echoes this theme. Classical theory predicts specialization degrades as model complexity increases beyond the interpolation threshold. Yet double descent demonstrates that massively overparameterized networks, trained to perfectly fit their data, generalize better than models at the traditional optimal point. Specialists in the classical regime perform well. Generalists in the overparameterized regime perform better still.

Evolutionary algorithms typically favor local search, climbing the nearest fitness peak through small mutations. This process usually drives specialization, just as my finches developed narrow feeding strategies. But when landscapes shift frequently, the organism that maintains flexibility explores the adjacent possible more successfully than the one locked into a single peak. Vikings discovered this principle empirically: raid when defenses are weak, trade when markets are open, offer military service when payment is generous. The ability to switch modes constituted an evolutionary strategy more robust than commitment to any single niche.

Is behavioral plasticity itself subject to natural selection? The evidence suggests that in fluctuating environments, the capacity to assess conditions and select appropriate strategies from a repertoire confers survival advantage. The Vikings did not choose between trader and raider. They chose both, contingently, just as the pizzly does not choose between seal hunting and berry foraging but switches as opportunity permits. In nature, as in history, it is not the strongest of the species that survives, but the most adaptable.