We investigated children's (n = 120; 3- to 11-year-olds) and adults' (n = 18) reasoning about life-cycle changes in biological organisms by examining their endorsements of four different patterns of life- span changes. Participants were presented with two separate tasks: (a) judging possible adult versions of a juvenile animal and (b) judging possible juvenile versions of an adult animal. The stimuli enabled us to examine the endorsement of four different patterns of change: identical growth, natural growth, dramatic change, and speciation. The results suggest that endorsement of the different patterns is influenced by age and familiarity. Young children and individuals confronted with unfamiliar organisms often endorsed an identical growth that emphasizes the stability of features over the life span and between parents and offspring. The results are interpreted as supporting the idea that cognitive constraints influence individuals' reasoning about biological change and that the influence of these constraints is most notable when individuals are young or are presented with unfamiliar biological organisms. [This paper was published in "Journal of Experimental Child Psychology" v173 p205-221 2018.]