Identifying what drives individual heterogeneity has been of long interest to us ecologists, evolutionary biologists and biodemographers, because only such identification provides deeper understanding of ecological and evolutionary population dynamics. In natural populations we are challenged to accurately decompose the generating genetically fixed and selectively neutral dynamic moments of heterogeneity. Rather than working on wild populations we present here data from a simple bacterial system in the lab, Escherichia coli. Our system, based on cutting-edge microfluidic techniques, provides high control over the genotype and the environment. Only such high control provides the means to unambiguously decompose and quantify fixed, genetic variability, and dynamic, stochastic variability among individual demographic components. We show that within clonal individual variability (neutral dynamic heterogeneity) in lifespan and lifetime reproduction is dominating at about 93-95%, over the 5-7% genetically (adaptive fixed) driven differences. The genetic differences among the clonal strains still lead to substantial variability in population growth rates (fitness), but the neutral variability slows adaptive change, by enhancing genetic drift, and lowering overall population growth. We also revealed a surprising diversity in demographic patterns among the clonal strains, which indicates diverse underlying stochastic cell-intrinsic processes that shape these demographic patterns. Such diversity is surprising since all cells belong to the same bacteria species, E. coli, and still exhibit patterns such as classical senescence, non-senescence, or negative senescence. We end by discussing whether similar levels of neutral variability might be detected in other systems and close by stating the open questions how such neutral heterogeneity is maintained, how it has evolved, and whether it is adaptive.