Breeder’s Equation

This approximation is a guesstimate, not a random guess. To determine h² in the absence of formal population data, start from direct observation and work through the following logic:

1. Evaluate environmental stability. Strong environmental sensitivity → lower h². Stable expression across environments → higher h².
2. Consider parent–offspring resemblance. Consistent resemblance → higher h². Weak or inconsistent resemblance → lower h².
3. Assess response to selection over time. Predictable population shifts → moderate to high h². Erratic or regressing gains → low h².
4. Judge environmental dominance. If environment overwhelms genetic differences → low h². If genetic differences persist despite noise → higher h².

Practical guide:
Low h² (≈ 0.1–0.2): environment-driven, inconsistent response
Moderate h² (≈ 0.3–0.5): mixed genetic and environmental control
High h² (≥ 0.6): genetically stable, predictable response

Over successive generations, observed selection response progressively refines h², making it increasingly accurate. For the first generation, without prior data, h² must be estimated using informed judgment.