扩展适应（英语：exaptation）是指在演化过程中一种特征的功能发生了变化。例如，如果一个特征最初演化出来是为了实现某种特定的功能，但后来它又有了另一种其他用途，就可称之为“扩展适应”。鸟类羽毛的演化便是一个经典的例子：羽毛最初是为了保温而演化出来的，但在后来羽毛变得开始适应于飞翔。另一个例子则是早期鱼类的肺，它们后来演化为陆生脊椎动物的肺，但同时还通过扩展适应成为了一些鱼类体内用来调节浮力的器官——鳔。

这一概念也被称为预适应（英语：pre-adaptation）。不过“预适应”这一术语隐含了目的论，与自然选择的基本原理相悖，故现以被“扩展适应”所取代。

Exaptation (a replacement for the teleologically-loaded term "pre-adaptation") and the related term co-option describe a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example: initially they may have evolved for temperature regulation, but later were adapted for flight. Interest in exaptation relates to both the process and products of evolution: the process that creates complex traits and the products (functions, anatomical structures, biochemicals, etc.) that may be imperfectly developed.