Most developmental research focuses on a few model organisms, among which the nematode Caenorhabditis elegans is particularly prominent. Until recently, C. elegans was viewed as the ultimate deterministic organism, because there is a virtual absence of variation in cell number (eutely). However, Azevedo et al. [1xThe demise of the platonic worm. Azevedo, R.B.R. et al. Nematology. 2000; 2: 71–79CrossrefSee all References[1] in their ‘Demise of the Platonic worm’, previously showed that the ‘platonic ideal’ of a worm, where each individual faithfully represents the essentialist idea of the species, does not hold true for all nematodes. The authors reported that, in the epidermis, the variance in cell number between individuals of a species increased with the mean cell number in that species.In a new article [2xA power law for cells. Azevedo, R.B.R. and Leroi, A. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 5699–5704Crossref | PubMed | Scopus (22)See all References[2], Azevedo and Leroi report that the variability in some supposedly eutelic taxa is not unusually low, and that the relationship between cell number variation and mean cell number generally follows a power law with an exponent of 2 across a wide range of multicellular taxa. They use stochastic branching processes to model the way in which variation builds up in a lineage and convincingly argue that the relationship between cell variability and cell number must be maintained by selection. In another new article, Delattre and Felix [3xPolymorphism and evolution of vulval precursor cell lineages within two nematode genera, Caenorhabditis and Oscheius. Delattre, M. and Felix, M.-A. Curr. Biol. 2001; 11: 631–643Abstract | Full Text | Full Text PDF | PubMed | Scopus (51)See all References[3] report variability in vulval cell lineages in several strains of C. elegans and of its close relative Oscheius sp. CEW1, and demonstrate that this variability is affected by several loci. Thus, lineage variability can even evolve over short evolutionary timescales.These studies are important for several reasons. First, they provide a solution to the paradox that the C. elegans nematode model displays no developmental variation, whereas there is variation in development among nematode species. The current results no longer exclude a standard neo-darwinian scenario where the gradual divergence of a developmentally polymorphic population can lead to species differences. Second, these studies dispel the notion that C. elegans can serve as the platonic model for all nematodes. Finally, these studies provide a framework for unraveling the genetic mechanisms underlying developmental stochasticity. It is perhaps ironic that animals known for their invariance should provide materials for a better understanding of the developmental basis of phenotypic variability. This would really please Aristotle. In his view, knowledge comes from understanding and classifying variation in the empirical world.