Gene duplica on is associated with the evolu on of many novel biological func ons at the molecular level. The dominant view, o en referred to as "neofunc onaliza on", is that duplica ons precede many novel gene func ons by crea ng func onally redundant copies which are less constrained than singletons. Numerous alterna ve models have been formulated, however, including several (such as "subfunc onaliza on" and "escape from adap ve constraints") in which novel func ons emerge prior to duplica on. Unfortunately, few studies have reconstructed the evolu onary history of a func onally diverse gene family sufficiently well to differen ate between these models. In order to understand how gene families evolve and to what extent they fit par cular evolu onary models, here we examined the evolu on of the g2 family of phospholipase A2 in 92 genomes from all major lineages of Vertebrata. This family is evolu onarily important and has been co-opted for a diverse range of func ons, including innate immunity and venom. The genomic region in which this family is located is remarkably syntenic. This allowed us to reconstruct all duplica on events over hundreds of millions of years of evolu onary history using a novel method to annotate gene clusters, which overcomes many limita ons of automa c annota on. Surprisingly, we found that even at this level of resolu on our data could not be unambiguously fit to exis ng models of gene family evolu on. This suggests that each model may describe a part-truth that doesn't capture the full complexity of gene family evolu on. Graphical abstract Introduc onPerhaps the most important goal in evolu onary biology remains the explana on of the origins of novelty -how do new func ons, traits, and ul mately organisms arise? Gene duplica on is widely considered one of the most important mechanisms facilita ng the evolu on of novel func ons (Ohno 1970;Innan and Kondrashov 2010) . However, duplica on itself is o en treated as a "black box" -a form of "random" muta on -and numerous apparently contradictory models have been ar culated to explain the fates of duplicate genes (Conant and Wolfe 2008;Innan and Kondrashov 2010) . Although discussion of duplica on and redundancy arguably goes back to Darwin (who had no knowledge of genes and spoke of redundant "organs") and has a rich history in the 20th Century (Taylor and Raes 2004) , the "neofunc onaliza on" model of Susumu Ohno has loomed large in the field of molecular evolu on since the publica on of the seminal text "Evolu on by Gene Duplica on" in 1970 (Ohno 1970) . Briefly, this model describes gene duplica on (a neutral process) facilita ng the genesis of novelty by crea ng func onally redundant gene copies which, no longer constrained by the func onal role of the molecule encoded by the "parent" gene, enjoy a period of relaxed selec on in which neutral muta ons may accumulate. Any poten ally beneficial muta ons acquired during this period of neutral change may then be fixed by posi ve selec on.

Over millennia, steppe nomadic tribes raided and sometimes overran settled Eurasian civilizations. Most polities formed by steppe nomads were ephemeral, making it difficult to ascertain their genetic roots or what present-day populations, if any, have descended from them. Exceptionally, the Khazar Khaganate controlled the trade artery between the Black and Caspian Seas in VIII-IX centuries, acting as one of the major conduits between East and West. However, the genetic identity of the ruling elite within the polyglot and polyethnic Khaganate has been a much-debated mystery; a controversial hypothesis posits that post-conversion to Judaism the Khazars gave rise to modern Ashkenazim. We analyzed whole-genome sequences of eight men and one woman buried within the distinctive kurgans of the Khazar upper (warrior) class. After comparing them with reference panels of present-day Eurasian and Iron Age populations, we found that the Khazar political organization relied on a polyethnic elite. It was predominantly descended from Central Asian tribes but incorporated genetic admixture from populations conquered by Khazars. Thus, the Khazar ruling class was likely relatively small and able to maintain a genetic identity distinct from their subjugated populations over the course of centuries. Yet, men of mixed ancestry could also rise into the warrior class, possibly providing troop numbers necessary to maintain control of their large territory. However, when the Khaganate collapsed it left few persistent genetic traces in Europe. Our data confirm the Turkic roots of the Khazars, but also highlight their ethnic diversity and some integration of conquered populations.