Technical Abstract: MicroRNAs (miRNAs) are small, single-stranded RNAs that downregulate target genes at the post-transcriptional level. miRNAs regulate target genes by guiding mRNA cleavage or by repressing translation. miRNAs play crucial roles in a broad range of developmental processes in plants. Multiple miRNAs are present in germinating seeds and seedlings of Arabidopsis, some of which are involved in the regulation of germination and seedling growth by plant hormones such as abscisic acid (ABA) and auxin. The involvement of miRNAs in ABA responses is not limited to the early stages of plant development but seems to be important for general stress responses throughout the plant life cycle. This Darwin review summarizes recent progress in miRNA research focusing on seed and stress biology, two topics which were of interest to Charles Darwin. In addition, a mutant released from miRNA repression provided insight into circumnutation (plant movement), another subject that piqued Darwin’s curiosity during his science career. The circumnutation phenotype observed in the miRNA mutant is also described in this review.