几乎所有动物都拥有“个性”，这会帮助它们应对环境，但是它们应对环境以及其他动物的程度有很大的差异。
Franz Weissing及其同事为这些个性如何随时间而发展以及为何反应高度敏捷并不总是最好的策略提供了一个进化论的解释。他们的结果解释了不同的个性如何可能在从鱼到鸟类再到小鼠甚至人类等动物身上出现。这组科学家利用一个简单的数学模型，该模型代表了不同情况下的一系列可能的选择和每个选择的回报。他们证明了当对环境反应敏捷的这种特征罕见的时候，它最有利，但是当这种特征常见的时候，它变得不利。该结果解释了为何反应敏捷和反应迟钝的个体可以在一个群体里共存。
这组作者还发现，反应敏捷常常是正反馈的，而且随着时间的推移而成本下降，这导致一些个体始终比另一些更加反应敏捷。因此自然选择导致了一个种群中的两个团体，其中一个在所有环境下都会对环境刺激做出反应，而另一个在很大程度上对刺激的反应迟钝。这组科学家提出这些反应敏捷程度的模式可能导致其它特征的相关性，例如大胆和侵略性，这为这样的相关性为何常常见于动物种群提供了一个解释。（生物谷Bioon.com）
生物谷推荐原始出处：
PNAS published October 6, 2008, doi:10.1073/pnas.0805473105
Evolutionary emergence of responsive and unresponsive personalities
Max Wolf, G. Sander van Doorn, and Franz J. Weissing
In many animal species, individuals differ consistently in suites of correlated behaviors, comparable with human personalities. Increasing evidence suggests that one of the fundamental factors structuring personality differences is the responsiveness of individuals to environmental stimuli. Whereas some individuals tend to be highly responsive to such stimuli, others are unresponsive and show routine-like behaviors. Much research has focused on the proximate causes of these differences but little is known about their evolutionary origin. Here, we provide an evolutionary explanation. We develop a simple but general evolutionary model that is based on two key ingredients. First, the benefits of responsiveness are frequency-dependent; that is, being responsive is advantageous when rare but disadvantageous when common. This explains why responsive and unresponsive individuals can coexist within a population. Second, positive-feedback mechanisms reduce the costs of responsiveness; that is, responsiveness is less costly for individuals that have been responsive before. This explains why individuals differ consistently in their responsiveness, across contexts and over time. As a result, natural selection gives rise to stable individual differences in responsiveness. Whereas some individuals respond to environmental stimuli in all kinds of contexts, others consistently neglect such stimuli. Interestingly, such differences induce correlations among all kinds of other traits (e.g., boldness and aggressiveness), thus providing an explanation for environment-specific behavioral syndromes.
