Crane, pheasant, peacock? Nope, that's a Hoatzin, and no one really knows where it came from. If we've learned anything from the history of science, some of our best lessons in genetics come from studying plants and animals. Birds are an especially useful subject for these sorts of studies because, typically, they have distinct physical characteristics. Even Charles Darwin famously wrote 'On the Origin of Species' after an expedition to the Galapagos where he studied the beaks of finches (a small bird) and developed what we now think of as modern evolutionary biology. A big part of Darwin's theory being that beneficial traits are selected naturally, and those that confer an advantage to an individual are passed on to their offspring. Those individuals are then said to increase their 'fitness,' which is a measure of reproductive success - more reproduction equals better fitness. So that means that traits are inherited and we can figure out the ancestral history of animals by successively grouping the ones that look alike together. At least that was the thinking in the mid-1800's. This ends up more or less becoming a tree where every branch has a distinct common ancestor and the things that all look alike are related. But, unfortunately, biology isn't that simple, nor is evolution. Because what's beneficial to one group or individual could be beneficial to another. And instead of inheriting a trait from an ancestor, two groups can develop that same trait independently of one another. There are many examples of this evolutionary process in action, a classic example of this being wings in bats, birds and insects. These are totally different animals who all evolved the ability to fly separately, but this developmental agreement on similar physical structures is called convergent evolution. While these things might look the same on the physical level, they're totally different on the molecular and genetic level! Fortunately, DNA sequencing can help suss out what's inherited and what's convergent, but in the case of the hoatzin, it's not so simple. Actually, all modern birds aren't so simple once we look at the genetics. It might seem easy to stick something that looks as weird as the Hoatzin off on its own, and group modern birds nicely into evolutionary branches based on their physical characteristics. But that's not what DNA sequencing tells us and modern birds seem to have hybridized so much that their evolutionary origins actually look a lot more like a network, or a bush, than they do a typical tree! Even the Hoatzin, which by all accounts should be stuck in a corner by itself, has genetic signatures that make its origins not totally obvious. It would seem that our view on evolutionary trees also needs to evolve. ### Suh A. 2016. "The phylogenomic forest of bird trees contains a hard polytomy at the root of Neoaves." DOI:10.1111/zsc.12213

@LabSpaces I remember all the problems the hoatzin caused from a phylogenetic standpoint! The sequencing was the easy part 🤣 I felt bad for the computational scientists on this one!