Wolpert L
Department of Anatomy and Developmental Biology, University College, London, UK.
Dev Suppl. 1994:79-84.
A scenario for the evolution of a simple spherical multicellular organism from a single eukaryotic cell is proposed. Its evolution is based on environmentally induced alterations in the cell cycle, which then, by the Baldwin effect, become autonomous. Further patterning of this primitive organism--a Blastaea, could again involve environmentally induced signals like contact with the substratum, which could then become autonomous, by, perhaps, cytoplasmic localization and asymmetric cell division. Generating differences between cells based on positional information is probably very primitive, and is well conserved; its relation to asymmetric cell division is still unclear. Differentiation of new cell types can arise from non equivalence and gene duplication. Periodicity also evolved very early on. The origin of gastrulation may be related to mechanisms of feeding. The embryo may be evolutionarily privileged and this may facilitate the evolution of novel forms. Larvae are secondarily derived and direct development is the primitive condition as required by the continuity principle.
本文提出了一个关于简单球形多细胞生物从单个真核细胞进化而来的设想。其进化基于环境诱导的细胞周期变化，然后通过鲍德温效应，这些变化变得自主。这种原始生物——囊胚体的进一步模式形成，可能再次涉及环境诱导信号，如与基质接触，然后这些信号可能通过细胞质定位和不对称细胞分裂而变得自主。基于位置信息产生细胞间差异可能非常原始，并且保守性良好；其与不对称细胞分裂的关系仍不清楚。新细胞类型的分化可能源于不等同和基因复制。周期性也很早就进化出来了。原肠胚形成的起源可能与摄食机制有关。胚胎在进化上可能具有优势，这可能促进新形态的进化。幼虫是次生衍生的，直接发育是连续性原则所要求的原始状态。
