Evidence Synthesis has seen an enormous increase recently, across many different scientific disciplines. Despite its popularity, it has also been the subject of significant criticism. One of the main critiques of evidence synthesis, is the existence and treatment of heterogeneity between primary studies. The aim of this paper is to re-examine heterogeneity in evidence synthesis, including perspectives from evolutionary biology, ecology and conservation. I argue that while some of the critiques of heterogeneity remain valid, there are contexts where it is much less problematic. Furthermore, I propose that heterogeneity can be useful, as analysing it can provide valuable information.