图5. 不同时刻下表型和基因型的频率分布。(a)表示状态量x₁(x₂)未分化初期某时刻的频率分布; (b)表示群体内的表型x₁在分化之后某时刻的频率分布; (c)表示群体内的基因型x₂在分化之后相同时刻的频率分布。假设对于原始物种A, 其任意在两个状态x₁和x₂随着时间的演化受到基因突变和随机漂变的影响, 在相同或不同时刻出现不同程度的分化。当我们处于物种进化的一个“切面”去观察时, 表型x₁分化成x₁₁和x₁₂, 并且进化依赖于特定的路径。若此时分化出的表型和基因型在数量统计上满足一定的条件, 同时在表型和基因型两个状态下同时具有特征x₁₁, x₂₁(x₁₁, x₂₂或x₁₂, x₂₁或x₁₂, x₂₂)的个体为新物种。

Fig. 5. Frequency distribution of phenotypes and genotypes at different time. (a) showing the frequency distribution curve of the state x₁(x₂) in the early differentiation. (b) demonstrating the frequency distribution curve of the phenotype x₁ at a certain moment after differentiation. (c) indicating the frequency distribution curve of the genotype x₂ at the same moment after differentiation. Suppose that any two states x₁ and x₂ of the original species A evolved influenced by random mutation and drift, then different degree of differentiation occurs in the same or different time. When observing in a “cutting plane” of a species evolution, we notice that x₁(x₂) differentiates into x₁₁(x₂₁) and x₁₂(x₂₂), and the evolution are path-dependent. Meanwhile, if the differentiated phenotypes and the genotypes in a quantity statistics satisfy certain conditions, the individuals with ${{x}_{11}},{{x}_{21}}({{x}_{11}},{{x}_{22}},or{{x}_{12}},{{x}_{21}},or{{x}_{12}},{{x}_{22}})$ are new species, respectively.