Rice S H
Department of Ecology and Evolutionary Biology, Yale University, New Haven, CT 06520, USA.
Proc Natl Acad Sci U S A. 1997 Feb 4;94(3):907-12. doi: 10.1073/pnas.94.3.907.
Heterochrony has become a central organizing concept relating development and evolution. Unfortunately, the standard definition of heterochrony--evolutionary change in the rate or timing of developmental processes--is so broad as to apply to any case of phenotypic evolution. Conversely, the standard classes of heterochrony only accurately describe a small subset of the possible ways that ontogeny can change. I demonstrate here that the nomenclature of heterochrony is meaningful only when there is a uniform change in the rate or timing of some ontogenetic process, with no change in the internal structure of that process. Given two ontogenetic trajectories, we can test for this restricted definition of heterochrony by asking if a uniform stretching or translation of one trajectory along the time axis superimposes it on the other trajectory. If so, then the trajectories are related by a uniform change in the rate or timing of development. If not, then there has been change within the ontogenetic process under study. I apply this technique to published data on fossil Echinoids and to the comparison of human and chimpanzee growth curves. For the Echinoids, some characters do show heterochrony (hypermorphosis), while others, which had previously been seen as examples of heterochrony, fail the test--implying that their evolution involved changes in the process of development, not just the rate at which it proceeded. Analysis of human and chimpanzee growth curves indicates a combination of neoteny and sequential hypermorphosis, two processes previously seen as alternate explanations for the differences between these species.
异时性已成为一个将发育与进化联系起来的核心组织概念。不幸的是，异时性的标准定义——发育过程速率或时间安排上的进化变化——过于宽泛，以至于适用于任何表型进化的情况。相反，异时性的标准类别仅准确描述了个体发育可能发生变化的一小部分方式。我在此证明，只有当某些个体发育过程的速率或时间安排发生一致变化，而该过程的内部结构没有变化时，异时性的命名才具有意义。给定两条个体发育轨迹，我们可以通过询问一条轨迹沿时间轴的均匀拉伸或平移是否能将其叠加在另一条轨迹上来检验异时性的这种受限定义。如果是，那么这两条轨迹通过发育速率或时间安排的一致变化相关联。如果不是，那么在正在研究的个体发育过程中就发生了变化。我将这种技术应用于已发表的关于化石海胆的数据以及人类和黑猩猩生长曲线的比较。对于海胆，一些特征确实表现出异时性（超形态发生），而其他一些先前被视为异时性例子的特征则未通过检验——这意味着它们的进化涉及发育过程的变化，而不仅仅是发育进行的速率。对人类和黑猩猩生长曲线的分析表明了幼态持续和顺序性超形态发生的结合，这两个过程先前被视为对这些物种之间差异的替代解释。
