Human life histories are believed to be made up of different levels of factors that contribute to the variation and evolution of human health, and this can be analyzed by classifying the various events of life in a rapid slow continuum (Promislow & Harvey, 1990 cited in Kaplan, Lancaster, & Robson, 2003). Mammals, for example, are at the fast end of the continuum and are known to reproduce early, have a shorter pregnancy period, grow to smaller body sizes, and produce large numbers of offspring vulnerable to death. On the other hand, species scattered at the other end of the continuum tend to have characteristics opposite to those of mammals (Kaplan et al., 2003). These changing momentums are generally explained by focusing on external forces, such as natural disasters, climate change, food availability, population density, and disease diversity. Furthermore, interactions between populations of species can also be considered a factor contributing to variation in the life histories of those populations (Kaplan et al., 2003). Furthermore, the external forces mentioned above could strengthen over a long period of time and this could influence the development of the species. However, there is evidence to indicate that, although these factors have brought benefits to human evolution, resulting in longer lifespans, there appear to be some trade-offs between costs and benefits to the species. For example, Shanley and Kirkwood (2000, cited in Kaplan et al., 2003) state that, even when there is abundant food during the later life cycle, when young rats are deprived of necessary calories, this is correlated with a delay in development resulting in reduced adult structures in later life. This essay will focus on human life… halfway through the article… In human evolution, it is essential to understand the main concepts of each theory. Works Cited Burger, O., Delong, J. P., & Hamilton, M. J. (2011). Industrial energy use and the history of human life. Scientific Reports, 1(56), 1-7. Hawkes, K., & Blurton Jones, N. (2005). Human age structures, paleodemography, and the grandmother hypothesis. In E. Voland, A. Chasiotis, & W. Schiefenhovel (Eds.), Grandmothering: The evolutionary significance of the second half of female life (pp. 118–140). Rutgers University Press.Kaplan, H., Lancaster, J., & Robson, A. (2003). Embodied capital and the evolutionary economics of the human lifespan. Population and Development Review, 29, 152-182. Retrieved from http://www.jstor.org/page/info/about/policies/terms.jspMarlowe, F. (2000). The patriarch hypothesis: an alternative explanation of menopause. Human nature, 11(1), 27-42.