Holocentric chromosomes, unlike monocentric chromosomes, attach spindle microtubules along their entire length; they have long been considered as a peripheral peculiarity with an unclear function. Zedek and Bureš summarise evidence that the key to their evolutionary role is the tolerance to fragmentation whereby holocentric chromosomes confer an advantage in times of exposure to cosmic radiation, desiccation and other chromosome-breaking factors.
They conclude that holocentric chromosomes may have played a major role in the evolutionary trajectory half a billion years ago; the first land colonisers had to cope with intense radiation and desiccation, and phylogenetic evidence suggests that holocentricity may underlie the resilient genetic makeup of the ancestors of land plants and animals.
Zedek, F., & Bureš, P. (2017). Holocentric chromosomes: from tolerance to fragmentation to colonization of the land. Annals of Botany, 121(1), 9–16. https://doi.org/10.1093/aob/mcx118