The target article offers a fresh perspective on development, arguing that it results from the ongoing interaction between changing individuals and their environments. The authors explain how environmental effects throughout a person’s life are not static. This view aligns with a selectionist approach and rejects essentialism (Rosales-Ruiz & Baer, Reference Rosales-Ruiz and Baer1997; Becker et al., Reference Becker, Kuhn and Pinkelman2024; Palmer & Donahoe, Reference Palmer and Donahoe1992), going beyond perspectives that see development as a fixed sequence of stages (Pascual-Leone, Reference Pascual-Leone1970). Instead, it highlights the interactive events involving evolving behavioral repertoires and environments that, although they may seem physically unchanged, actually alter in their function or role over time.

From a neuroscientific angle, the perspective described by the authors aligns with evidence showing that, far from being rigid and fixed computing machines, brains are highly adaptable and continuously change based on interactions with the environment (Merzenich et al., Reference Merzenich, Kaas, Wall, Nelson, Sur and Felleman1983; Buonomano & Merzenich, Reference Buonomano and Merzenich1998; Powers et al., Reference Powers, Hays, Rosenfield, Porter, Gallaway, Chauvette and Rennaker2025; Kilgard et al., Reference Kilgard, Epperson, Adehunoluwa, Swank, Porter, Pruitt and Rennaker2025). For example, cortical maps adapt according to the ecological importance of environmental elements (Kilgard & Merzenich, Reference Kilgard and Merzenich1998a, Reference Kilgard and Merzenich1998b). In other words, the same element – seen or heard in many past instances – can suddenly trigger a noticeable change at the cortical level when it gains ecological relevance. The implications of neural plasticity for development are significant (Marzola et al., Reference Marzola, Melzer, Pavesi, Gil-Mohapel and Brocardo2023). Importantly, these findings go beyond early development and remain valid throughout the entire lifetime (Lee et al., Reference Lee, Basak, Grant, Ray, Skolasinska, Oehler and Voss2024).

Societies typically create socio-cultural environments that change the relevance of contextual stimuli over time, leading to some predictable yet not inherently inevitable patterns. For example, parents and the surrounding socio-verbal community tend to encourage a newborn’s vocalizations by giving selective attention to speech behavior (Warlaumont et al., Reference Warlaumont, Richards, Gilkerson and Oller2014). Children’s environments generally become enriched, with play behavior playing a key role (e.g., Pellegrini, Reference Pellegrini2009). Conversely, after adolescence, rigid and predictable patterns are socially favored, play behavior is often seen as immature and stigmatized (Deterding, Reference Deterding2018), and unpredictability tends to be eliminated from individual behavior patterns. As habits – defined here as highly repetitive behavioral patterns – develop during adulthood, the lack of environmental enrichment, stimulus novelty, and social attention and acceptance for unpredicted or unusual behavior often becomes the norm.

Sedimented behavioral patterns – according to neuroplasticity research – may initiate a harmful feedback loop, where decreased plasticity leads to less behavioral variation. This reduction may further diminish the chances of reinforcing new behaviors, causing an even greater decline in neuroplasticity. This problem worsens when considering the lack of contingencies for new learning in elderly behavior, which often becomes extremely rigid and predictable. As a result, it reduces the likelihood of environment-induced brain plasticity, perhaps because neuromodulatory systems involved in plasticity are susceptible to novel and discrepant stimuli (Sara, Reference Sara2009; Schultz, Reference Schultz2007; Donahoe, Reference Donahoe2017).

Gerontology research faces a significant challenge in promoting healthy levels of novel behavior, particularly since society often discourages new behaviors among the elderly and reinforces highly predictable patterns (North & Fiske, Reference North and Fiske2013). The probability of cognitive decline in the population genetically predisposed to dementia was found to decrease in a longitudinal study examining engagement in productive activities (Zhang et al., Reference Zhang, Fu, Ding, Lutz, Zeng and Yao2021). Notably, another study involving individuals over 65 years old found that non-physical productive and social activities were as protective against mortality as physical activities (Glass et al., Reference Glass, De Leon, Marottoli and Berkman1999).

Research has shown that proper training can halt and potentially reverse several processes involved in brain aging (Mishra et al., Reference Mishra, de Villers-Sidani, Merzenich and Gazzaley2014; de Villers-Sidani, Reference de Villers-Sidani, Mishra, Zhou and Voss2016; Voss et al., Reference Voss, Thomas, Cisneros-Franco and de Villers-Sidani2017). Additionally, neurogenesis – the creation of new neurons in the hippocampus and olfactory bulb – and the production of Brain-Derived Neurotrophic Factor, a protein crucial for synaptic plasticity, are both affected by physical activity (Baldwin & Greenwood, Reference Baldwin and Greenwood2020; Ruiz-Gonzalez et al., Reference Ruiz-Gonzalez, Hernandez-Martinez, Valenzuela, Morales and Soriano-Maldonado2021; Van Praag, Kempermann, & Gage, Reference Van Praag, Kempermann and Gage1999). These findings, along with research on cumulative hierarchical learning (Hixson, Reference Hixson2004) and behavioral “cusps” (Rosales-Ruiz & Baer, Reference Rosales-Ruiz and Baer1997; Becker et al., Reference Becker, Kuhn and Pinkelman2024), can promote even stronger boundary-bridging collaborations (Ortu & Vaidya, Reference Ortu and Vaidya2017) across various levels of analysis concerning neuroplasticity in evolving ecologies.

The concept of behavioral cusps is a particularly promising candidate for exploring neuro-behavioral changes during development. Rosales-Ruiz and Baer (Reference Rosales-Ruiz and Baer1997), from a purely behavioral viewpoint, mention that “What makes a behavior change a cusp is that it exposes the individual’s repertoire to new environments, especially new reinforcers and punishers, new contingencies, new responses, new stimulus controls, and new communities of maintaining or destructive contingencies. When some or all of those events happen, the individual’s repertoire expands.” From this perspective, what leads to a new stage in development is not an internally derived invariant sequence but the acquisition of new skills that can lead to further and greater enrichment of the repertoire (e.g., reading, walking, speaking). Although the concept has so far prompted a significant body of research in populations with developmental disabilities (e.g., Bosch & Fuqua, Reference Bosch and Fuqua2001), neuroscientific studies investigating plasticity during development could examine structural changes (including neurogenesis, Brain-Derived Neurotrophic Factor-Related plasticity, and remyelination) that occur as a result of behavioral cusps.

In summary, the causal dynamics involved in the neuro-behavioral-ecological development of the repertoire do not necessarily produce a fixed set of inevitable stages (e.g., Zhou et al., Reference Zhou, Panizzutti, de Villers-Sidani, Madeira and Merzenich2011). The interaction between biological factors and changing ecologies may create the impression of an unavoidable developmental sequence. However, as neuroplasticity research shows, these are not only flexible but can also be potentially reversible under the right ecological conditions. To investigate that interaction, we suggested some potential for boundary-bridging research investigating brain plasticity in relation to behavioral cusps. In general, as the authors of the target article suggest, the scientific investigation of repertoire changes during the lifetime should shift from considering contextual influences as static and essential to focusing on the iterative interaction between changing behaviors and changing environments.