Adaptive Landscape & de Finetti Diagram — 2D Heterozygote Advantage

This 2D companion to the Balancing Selection 3D sim swaps the population-as-spheres rendering for the two visualizations population geneticists actually reach for when reasoning about overdominance. A rolling-ball adaptive landscape shows mean population fitness w̄ as an exact analytic function of allele frequency, peaking precisely at the equilibrium q* = s₁/(s₁+s₂) — selection is literally a ball rolling uphill on this curve. A de Finetti triangle plots the population's genotype frequencies directly in barycentric coordinates against the Hardy-Weinberg parabola, so genetic drift is visible as scatter of the population's point away from that curve rather than as noisy individual sprites. A third panel runs 20 independent replicate populations forward under the same discrete Wright-Fisher recursion (selection then finite-population binomial sampling) to show, numerically, how much a small population's trajectory can wander from the deterministic no-drift curve before both settle near the same equilibrium.