How a protist (unicellular eukaryote) gave rise to animals is a major evolutionary question. To address this, we first need to unravel how the unicellular ancestor was, that is how it was morphologically and which genes it had. A question worth addressing is whether the unicellular ancestor already had some of the genes that are key to animal development and animal multicellularity. In other words, were the genes involved in cell adhesion, cell communication, and cell differentiation already present in the ancestor or are they invented by animals? The only way to address this, is to compare the genomes of animals with the genomes of their closest unicellular relatives, and this inferring which genes are shared between animals and their unicellular cousins (therefore present in the ancestor) and which genes are exclusive to animals (therefore an animal innovation).