Parent offspring is expected to be highest during the parental investment period. Parent-offspring conflict assumes there will be "disagreements" between parents and offspring about how long parental investment lasts, how resources are allocated, and maintaining the life history trade-offs in the process. Allomaternal care Parental investment provided by individuals other than mothers and fathers is considered allocare. Both paternal care and allocare can reduce the energetic costs of parenting for mothers. Allocare is often referred as allomaternal care or allomothering if it is provided by anyone other than the mother. Based on Kin Selection Theory, it is usually assumed that mothers have been ancestrally necessary to ensure offsprings survival and reproduction. It is less known to what extent paternal investment or care or other types of allocare are a necessity to offspring survival and reproduction. Typically maternal care is defined at the most basic level of pregnancy and birth and lactation, but includes other things like provisioning, learning (in humans), mirroring (mirroring behavior of mother), and holding, carrying, and touching. It has been shown in various studies that allocare can take many forms such as provisioning, providing food, reducing parental costs for parents, time investments, economic investments, and other types of care such as holding. There have been different results from studies in traditional societies and natural fertility populations, than in industrialized societies. Allomaternal care has been hypothesized to have influenced ancestral evolution by being associated with increased brain size. Allomaternal care is also a part of a larger hypothesis of humans as cooperative breeders whereby allocare discounts the individual costs of parenting, especially when sets of parents have children around the same time as each other, or have other kin or community members to provide care (see grandmother hypothesis). Cooperative breeding is a social system that given some advantage over time, and cooperative breeding is much more common in humans and relatively rare in other mammalian species. Traits in our species that favor cooperative breeding evolve over time due to altruism, and within the context of kin selection and reciprocity. Lactation Lactation is one of the costliest forms of parental investment because it is taxing at a metabolic and physiological level, but also in terms of time and emotion as well. There are many trade-offs regarding lactation, and recent work has explored cost benefit models and thresholds for breastfeeding. From a biological and evolutionary perspective, breastfeeding infants is biologically