Cumulative cultural evolution and mechanisms for cultural selection in wild bird songs

Abstract

Cumulative cultural evolution, the accumulation of sequential changes within a single socially learned behaviour that results in improved function, is prominent in humans and has been documented in experimental studies of captive animals and managed wild populations. Here, we provide evidence that cumulative cultural evolution has occurred in the learned songs of Savannah sparrows. In a first step, “click trains” replaced “high note clusters” over a period of three decades. We use mathematical modelling to show that this replacement is consistent with the action of selection, rather than drift or frequency-dependent bias. Generations later, young birds elaborated the “click train” song form by adding more clicks. We show that the new songs with more clicks elicit stronger behavioural responses from both males and females. Therefore, we suggest that a combination of social learning, innovation, and sexual selection favoring a specific discrete trait was followed by directional sexual selection that resulted in naturally occurring cumulative cultural evolution in the songs of this wild animal population.

Language-like efficiency and structure in house finch song

“…Outside of linguistics, efficiency and complexity are often discussed in relation to cumulative cultural evolution (CCE). Definitions of CCE vary and a full review is outside of the scope of this study, but I will use the definition of Williams et al [ 113 ]: “the accumulation of sequential changes within a single socially learned behavior that results in improved function”. Discussions of CCE often focus on increasing complexity over time [ 114 ], which was once thought to be a hallmark of human culture [ 115 ] but has now been observed in several non-human communication systems including humpback whale [ 116 ] and Savannah sparrow song [ 113 ].…”

Recovery of cirl bunting, Emberiza cirlus, song diversity after translocation

“…Even if abnormal songs are produced by the first few generations of translocated birds, recovery to a normal song repertoire size may be possible (but see Baker, 1996). In addition, as new syllables/songs develop during population expansion in a translocated songbird (Mundinger, 1980; Williams et al, 2022; Williams & Lachlan, 2022) species‐typical sounds may be preferentially selected for during the babbling phase because they perform their function better, that is, attract a female or repel a rival (Nelson & Marler, 1994). Although we did not assess female song preferences in our study, it is important to remember that females also develop song preferences based on what they hear, often during a critical phase (see Nowicki & Searcy, 2004).…”

What made us “hunter-gatherers of words”

“…While I agree with them that these are essential ingredients of the cultural process, I do not think self-domestication was critical in their emergence, for they strike me as too generic and widespread in the animal kingdom. It is true that their effects have been studied with animals in (“artificial”) experimental settings that may make one think of human influence and domestication (Fehér et al, 2009 ; Claidiere et al, 2014 ), but it is also possible to find them in the wild (Whiten, 2019 , 2021 ; Williams and Lachlan, 2022 ; Williams et al, 2022 ). Thomas and Kirby ( 2018 )'s intuition that self-domestication affected the cultural process strikes me as being on the right track, but the effect we should be looking for must be more specific than they claim.…”