This study presents a self-organizing model of group formation in three-dimensional space, used to investigate the spatial dynamics of animal groups such as fish schools and bird flocks. The model reveals major group-level behavioural transitions related to minor changes in individual-level interactions. It also presents the first evidence for collective memory in such groups, where the previous history of group structure influences collective behaviour as individual interactions change. The model shows how differences among individuals influence group structure and how individuals using simple, local rules can accurately change their spatial position within a group. These results are considered in the context of the evolution and ecological importance of animal groups. The model simulates individual-based behaviour based on local repulsion, alignment, and attraction tendencies. It uses three zones: a zone of repulsion (to maintain personal space), a zone of orientation (to align with neighbours), and a zone of attraction (to move towards others). The model exhibits characteristic collective behaviours similar to those of natural groups when certain parameters are changed. The study discusses how these different types of collective behaviour influence individual fitness within groups and reveals a novel form of collective memory, where the previous history of group structure influences collective behaviour even without knowledge of that history. The spatial structuring within groups has important ecological and evolutionary consequences. The model shows that individual differences in speed, turning rate, error, and zone sizes influence spatial positions within groups. The study also investigates how these differences affect the group's structure and how individuals can change their position based on local information. The results suggest that individuals with different behavioural tendencies tend to occupy different positions within the group, such as the front, centre, or periphery. The model demonstrates that collective behavioural transitions occur in response to changes in individual interactions. The study highlights the importance of previous group history in influencing future collective behaviour, even without explicit knowledge of that history. This hysteresis phenomenon may be an unexplored property of real animal groups. The study also discusses the implications of these findings for understanding the evolution of behaviour in grouping organisms. The results suggest that individual differences in behaviour and movement properties can lead to self-sorting within groups, which may explain observed patterns in natural animal aggregations. The study also highlights the potential for parasites to manipulate the positions of individuals within groups, as seen in the case of parasitized killifish. The model provides potential mechanisms for understanding how individuals modify their behaviour in such situations.This study presents a self-organizing model of group formation in three-dimensional space, used to investigate the spatial dynamics of animal groups such as fish schools and bird flocks. The model reveals major group-level behavioural transitions related to minor changes in individual-level interactions. It also presents the first evidence for collective memory in such groups, where the previous history of group structure influences collective behaviour as individual interactions change. The model shows how differences among individuals influence group structure and how individuals using simple, local rules can accurately change their spatial position within a group. These results are considered in the context of the evolution and ecological importance of animal groups. The model simulates individual-based behaviour based on local repulsion, alignment, and attraction tendencies. It uses three zones: a zone of repulsion (to maintain personal space), a zone of orientation (to align with neighbours), and a zone of attraction (to move towards others). The model exhibits characteristic collective behaviours similar to those of natural groups when certain parameters are changed. The study discusses how these different types of collective behaviour influence individual fitness within groups and reveals a novel form of collective memory, where the previous history of group structure influences collective behaviour even without knowledge of that history. The spatial structuring within groups has important ecological and evolutionary consequences. The model shows that individual differences in speed, turning rate, error, and zone sizes influence spatial positions within groups. The study also investigates how these differences affect the group's structure and how individuals can change their position based on local information. The results suggest that individuals with different behavioural tendencies tend to occupy different positions within the group, such as the front, centre, or periphery. The model demonstrates that collective behavioural transitions occur in response to changes in individual interactions. The study highlights the importance of previous group history in influencing future collective behaviour, even without explicit knowledge of that history. This hysteresis phenomenon may be an unexplored property of real animal groups. The study also discusses the implications of these findings for understanding the evolution of behaviour in grouping organisms. The results suggest that individual differences in behaviour and movement properties can lead to self-sorting within groups, which may explain observed patterns in natural animal aggregations. The study also highlights the potential for parasites to manipulate the positions of individuals within groups, as seen in the case of parasitized killifish. The model provides potential mechanisms for understanding how individuals modify their behaviour in such situations.