 A parallel development, initiated again by Fisher and Wright, as well as by J.B.S. Haldane, involved mathematical models of theoretical genotypes at one or a few loci each contributing to the parameters for surviving and leaving offspring. In this field, which came to be known as Population Genetics, estimation of selection coefficients of genotypes inferred from distinct phenotypes was possible, albeit more readily when the populations were subject to artificial selection in the laboratory than when frequencies or changes over time were observed in the wild (which was studied in the new field of ecological genetics). Just as in quantitative genetics, the focus in population genetics was on difference in traits; complexities of development in its ecological context were typically collapsed into the parameters of the models.