After the end-Permian extinction — the most severe biotic crisis in Earth's history — marine organisms appeared to shrink. The pattern was named the Lilliput effect and interpreted as a universal dwarfing response: environmental stress forced surviving species to become smaller. Foster, Prinoth, Kustatscher, and Hautmann measured 4,833 individual bivalve specimens from 72 species in the Dolomites of northern Italy and found that the Lilliput effect is real but its mechanism is wrong.
Surviving species did not shrink. The three bivalve lineages that persisted through the extinction boundary showed no statistically significant decrease in body size. Some grew slightly larger. The observed reduction in average body size at the genus level — approximately 0.25 logarithmic units — was driven entirely by the origination of new, smaller species in the aftermath. The community became smaller not because its members shrank but because its new arrivals were small.
Recovery occurred in two phases separated by roughly two million years. In the late Griesbachian, surviving species increased in size — the incumbents grew. In the early Spathian, larger-bodied species evolved for the first time since the extinction — the newcomers caught up. The size reduction was a demographic phenomenon, not a physiological one. Faunal turnover, not within-species dwarfing, produced the pattern.
The through-claim applies wherever average properties shift across a disruption. When the mean size of a population changes, the instinctive interpretation is that individuals changed. But the mean can shift through replacement alone — old members maintaining their character while new, differently sized members enter the system. The change in the average does not require a change in anyone. It requires only a bias in who arrives.