Mehr et al. contend that infant-directed (ID) singing arose as a credible acoustic signal of maternal attention and provided an impetus for the emergence of melody. They emphasize the divergent interests of infant and mother – infants wanting more attention than mothers care to provide. The historical record, however, is at odds with this contention. Infant carrying has been central to infant well-being and survival for most of human history, promoting safety, thermoregulation, and arousal regulation. Ubiquitous infant carrying, both in the past and in contemporary foraging cultures (e.g., Aka of Central Africa) co-occurs with frequent feeding, prolonged breastfeeding (yielding greater interbirth intervals), and prompt responsiveness to infant distress, resulting in less infant crying and more sleeping than infants in nearby (Nganda) farming communities whose mothers exhibit less proximal interaction but somewhat more distal interaction such as vocalizing (Hewlett, Lamb, Shannon, Leyendecker, & Schölmerich, Reference Hewlett, Lamb, Shannon, Leyendecker and Schölmerich1998). These caregiving differences are not attributable to differences in environmental hazards or infant mortality, which are comparable. Incidentally, the carrying and feeding frequency of Nganda farming mothers greatly exceeds that of Western mothers. In any case, foraging mothers provide considerably more attention than demanded by infants. Moreover, complaints about the burdens of infant care are relatively rare in such societies and more common in affluent Western societies. Also notable is the more egalitarian social structure of foraging societies than farming or industrial societies, with foragers sharing caregiving and provision-seeking in their tightly knit communities.

ID singing likely emerged in conjunction with carrying in the foraging communities of the distant past. Accordingly, such singing would be multimodal rather than the acoustic signal envisioned by Mehr et al. Moreover, one would expect the rhythm of movement to influence the rhythm of singing (Ayres, Reference Ayres1973). Interestingly, rhythmic movement such as brisk walking calms human and other mammalian infants more effectively than stationary holding (Esposito et al., Reference Esposito, Yoshida, Ohnishi, Tsuneoka, Rostagno and Kuroda2014). In a recent cross-cultural study of mother–infant dyads from several developed countries, mothers systematically responded to distressed infants by picking them up and talking (Bornstein et al., Reference Bornstein, Putnick, Rigo, Esposito, Swain and Venuti2017). Although these mothers sang to their infants, they did so in playful rather than soothing contexts (Bornstein, personal communication, November 13, 2017). In a laboratory study in which infant distress was induced, and mothers were restricted from picking up infants but allowed to touch them, maternal singing of familiar songs reduced infant distress more effectively than unfamiliar songs, which were more effective than ID speech accompanied by affectionate touch (Cirelli & Trehub, Reference Cirelli and Trehub2020). Repetition and predictability, which are crucial in parent–infant interactions, are also central to music and its appeal (Margulis, Reference Margulis2014).

Western mothers' interactions with infants are often distal, and their singing commonly occurs in face-to-face contexts, with mutual gaze potentially compensating for the absence of physical contact (Konner, Reference Konner2010). Falk (Reference Falk2004) has proposed that ID vocalizations arose to enable hominin mothers to put their baby down in service of efficient foraging – keeping in touch without tactile or eye contact. Indeed, ID singing is notably expressive and recognizable, with its warm vocal timbre, temporal regularity, and highly stereotyped performances (Bergeson & Trehub, Reference Bergeson and Trehub2002; Trainor, Clark, Huntley, & Adams, Reference Trainor, Clark, Huntley and Adams1997; Trehub, Plantinga, & Russo, Reference Trehub, Plantinga and Russo2016). Such singing commonly occurs in conjunction with coordinated rhythmic movement (Longhi, Reference Longhi2009) and smiling (Trehub et al., Reference Trehub, Plantinga and Russo2016).

In the absence of carrying, mutual gaze, or rhythmic movement, ID singing is not energetically costly. Songs for infants are melodically, rhythmically, and textually simple and repetitive (Sakata, Reference Sakata and Koskoff1987; Unyk, Trehub, Trainor, & Schellenberg, Reference Unyk, Trehub, Trainor and Schellenberg1992), and they are often sung with meaningless syllables (Brown, Reference Brown and Sadie1980; Finnegan, Reference Finnegan1977). In fact, it is not unusual for mothers to engage in other demanding activities (e.g., driving a car) while singing to infants (e.g., in out-of-view car seats), so the notion of ID singing as a costly and credible signal of maternal investment or attention remains unconvincing.

ID singing may be as important for mothers as for infant listeners. For example, singing in a soothing manner (lullaby style) reduces arousal levels in mothers as well as infants (Cirelli, Jurewicz, & Trehub, Reference Cirelli, Jurewicz and Trehub2020), and maternal calming may accelerate infant calming. Similarly, lively play songs may have energizing or euphoric consequences for the dyad. In situations when other emotional outlets are unavailable, the one-on-one context enables singers to vent their grievances by improvising the lyrics of songs to prelinguistic listeners (e.g., Masuyama, Reference Masuyama1989).

The rewarding nature of musical engagement was notably absent from the maternal-attention signaling and coalition-signaling aspects of the Mehr et al. account. According to Merker, Morley, and Zuidema (Reference Merker, Morley and Zuidema2015), any theory of the origins of music must account for its motivational core, as reflected in the universal tendency to gather for group singing and dancing unless there are societal prohibitions for doing so. These group musical contexts, including dyadic musical interactions, provide opportunities for coordinating arousal levels and emotions and reinforcing the solidarity of participants.

If ID singing evolved, at least in part, as an acoustic signal of maternal attention, as claimed by Mehr et al., one would expect it to show greater efficacy in attenuating infant distress than rhythmic but non-melodic vocalizations (e.g., rhythmic shushing), rhythmic movement (e.g., rocking and jiggling), holding with or without affective touch (e.g., stroking), and transport (e.g., carrying while walking). These comparisons, which are readily testable, should reveal whether ID singing is a primary component of infant care and therefore a possible signal of parental investment or whether it is an embellishment superimposed on other, more basic forms of infant care.

In contrast to Mehr et al., the Savage et al. companion paper is broadly applicable to musical functions, past and present, which typically involve affiliative or social bonding activities. Savage et al. are also flexible about the timeline, precedence, and relative contributions of cultural and biological evolution, according primacy to the former. Moreover, in characterizing music as multimodal, incorporating sound and movement rather than sound alone, and according a central role to music-making, sociality, and their rewarding consequences, their account is more aligned with the perspectives outlined in this commentary.