Much like a family tree depicts kinships between individuals, a phylogenetic tree, or phylogeny, represents the branching evolutionary relationships between life forms past and present. The relatedness of any two modern species (the spindliest, outermost twigs) can be gleaned by tracing their parental branches back to where they meet at a shared ancestor. Biologists now have a pretty good idea of the overall branching pattern, but some untangling is still required: can all animals be traced back to a jellyfish-like ancestor or a sponge-like one? SB
Yellow hedgehog sponge: who do you think you are?