increase mortality rates, vespertilionidae counteracts their environmental conditions through the evolutionary adaptation of dizygotic twins. the prevalence of dizygotic twinning in monkeys is thought to be an “insurance adaptation” for mothers reproducing at the end of their fertile years. while dizygotic twinning has been observed in species such as gorillas and chimpanzees, monkeys in the cebidae genus are found to be more likely to produce twins because of their small size and insect-based diet (varella, 2018). this is because their small size indicates shorter gestation periods and the rapid maturation of offspring, resulting in a shorter lifespan where organisms are rapidly replaced by newer generations. the smaller size of the cebidae genus also makes these species more susceptible to predators, thus triggering the heightened pace of birth, maturation, reproduction, and death. meanwhile, cebidae's insectivorous existence can be correlated with this genus's heightened ability to reproduce, as more resources become available, more organisms can take advantage of these resources. thus, monkeys that are smaller and have more access to food, such as the cebidae genus, have the ability to produce more offspring at a quicker pace. in terms of dizygotic twinning, it has been observed that older mothers within the cebidae genus have a higher chance of producing twins than those at the beginning stages of their fertility. despite their access to resources, the cebidae genus has a high mortality rate attributed to their size, meaning that in order to “keep up” their quickened lifecycle, they must produce an excess of offspring in ensuring generational survival. the positively-selected adaptation of twinning counteracts the genus's high mortality rate by giving older mothers the chance to produce more than one offspring. this not only increases the likelihood that one or more of these offspring will reach reproductive maturity, but gives the mother a chance to birth at least one viable offspring despite their age. due to their short life cycles, the cebidae genus is more inclined to produce dizygotic twins in their older reproductive years, thus signaling that the trait of high twinning propensity is one that is passed down in service of this genus's survival.