Bdelloid rotifers appear to have existed without sexual recombination for tens of millions of years. During this time they evolved into more than 400 morphologically and physiologically diverse species, and can now be found in almost any freshwater habitat throughout the world. Bdelloids are degenerate tetraploids with two ancient genome lineages (probably the result of whole genome duplication) that each has two copies, which may have begun to diverge when bdelloids abandoned meiosis and syngamy. While there has been considerable gene loss and/or rearrangement between the ancient lineages, there is perfect colinearity of genes between either of the two pairs of genomes. This colinearity may be maintained by the need for templates during DNA double-strand break repair, itself necessitated by the frequent desiccation of bdelloids in their ephemerally aquatic habitats. One result of this genome structure is that genes are maintained in multiple copies much longer than after traditional duplication events. Consistent with the expected trajectory of duplicated genes, many bdelloid genes appear to have copies that have diverged in function, while others show evidence of surprisingly strong purifying selection. The functional divergence between copies of many genes implies a very high homozygotic load if the genome pairs were segregating haplotypes. It also suggests that bdelloids may be capable of a broad phenotypic response independent of the increased phenotypic variance provided to populations by sexual recombination. How such extensive selection can occur efficiently at multiple completely linked loci remains a mystery.