Center for Systems and Control, College of Engineering, Peking University, Beijing 100871, China.
Center for Mathematical Biology, University of Pennsylvania, Philadelphia, PA 19104.
Proc Natl Acad Sci U S A. 2023 Mar 21;120(12):e2216218120. doi: 10.1073/pnas.2216218120. Epub 2023 Mar 16.
The concept of fitness is central to evolution, but it quantifies only the expected number of offspring an individual will produce. The actual number of offspring is also subject to demographic stochasticity-that is, randomness associated with birth and death processes. In nature, individuals who are more fecund tend to have greater variance in their offspring number. Here, we develop a model for the evolution of two types competing in a population of nonconstant size. The fitness of each type is determined by pairwise interactions in a prisoner's dilemma game, and the variance in offspring number depends upon its mean. Although defectors are preferred by natural selection in classical population models, since they always have greater fitness than cooperators, we show that sufficiently large offspring variance can reverse the direction of evolution and favor cooperation. Large offspring variance produces qualitatively new dynamics for other types of social interactions, as well, which cannot arise in populations with a fixed size or with a Poisson offspring distribution.
适合度的概念是进化的核心，但它只量化了个体将产生的预期后代数量。实际后代数量也受到人口随机性的影响，即与出生和死亡过程相关的随机性。在自然界中，繁殖力更强的个体往往在其后代数量上具有更大的变异性。在这里，我们为两种类型在非恒定大小的种群中竞争的进化开发了一个模型。每种类型的适合度由囚徒困境博弈中的成对相互作用决定，而后代数量的方差取决于其平均值。尽管在经典的种群模型中，由于背叛者的适合度总是大于合作者，因此它们被自然选择所偏好，但我们表明，足够大的后代方差可以改变进化的方向并有利于合作。对于其他类型的社会互动，大的后代方差也会产生定性上的新动态，而在具有固定大小或泊松后代分布的种群中则不会出现这种情况。
