一项研究报告说，从单细胞到多细胞的转变的最初关键步骤的进化速度可能比此前认为得更快。
William C. Ratcliff及其同事让单细胞酵母酿酒酵母（Saccharomyces cerevisiae）生活在一种环境中，在这种环境中，多细胞被认为是一种适应性的性状，这是建立在一个事实的基础上，即酵母细胞集群比单个细胞在液体中的定居速度更快。在60天的快速定居选择中，全部实验酵母种群都以多个附着细胞的雪花样集群为主，这是由在细胞分裂之后仍然相互粘着的细胞形成的。
这种集群显示出了几种多细胞性状，包括通过产生雪花样子代集群的多细胞“生殖芽”进行繁殖以及一个幼年阶段的出现。当定居选择的强度发生变化的时候，雪花酵母通过在多细胞层次而非单细胞层次上对变化进行了适应，这表明整个细胞集群作为一个整体进行进化。
这组科研人员还观察到了集群内部的劳动分工的进化：大多数细胞仍然活着并能进行繁殖，但是少部分细胞进行了程序细胞死亡，或者说细胞凋亡。凋亡的细胞起到了多细胞集群中的断裂点的作用，让雪花酵母调控它们产生的后代的数量和尺寸。
这些发现提示多细胞复杂性的关键特性可以在一种单细胞真核细胞中容易地进化出来。(生物谷Bioon.com)
doi: 10.1073/pnas.1115323109
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Experimental evolution of multicellularity
William C. Ratcliffa,1, R. Ford Denisona, Mark Borrelloa, and Michael Travisanoa,b
Multicellularity was one of the most significant innovations in the history of life, but its initial evolution remains poorly understood. Using experimental evolution, we show that key steps in this transition could have occurred quickly. We subjected the unicellular yeast Saccharomyces cerevisiae to an environment in which we expected multicellularity to be adaptive. We observed the rapid evolution of clustering genotypes that display a novel multicellular life history characterized by reproduction via multicellular propagules, a juvenile phase, and determinate growth. The multicellular clusters are uniclonal, minimizing within-cluster genetic conflicts of interest. Simple among-cell division of labor rapidly evolved. Early multicellular strains were composed of physiologically similar cells, but these subsequently evolved higher rates of programmed cell death (apoptosis), an adaptation that increases propagule production. These results show that key aspects of multicellular complexity, a subject of central importance to biology, can readily evolve from unicellular eukaryotes.
