Wild populations are subject to environments that are changing at unprecedented rates. Assessing natural selection and the capacity to adapt in wild populations is crucial to planning for and understanding how species will fare under climate change. The goal of this research was to empirically examine selection and adaptive capacity in a natural population of Chamaecrista fasciculata. In Chapter 1, I present an empirical quantitative genetic study of C. fasciculata to predict the rate of change in mean fitness using Fisher’s Fundamental Theorem of Natural Selection (FTNS). The additive genetic variance for fitness was found to be substantial and statistically significant in both 2013 and 2014. Application of FTNS predicts increases in mean fitness of 1.68 (2013) seeds and 8.08 (2014) seeds in the next generation. These findings demonstrate that this population has the genetic capacity to respond to natural selection and is predicted to increase in fitness and thus, become better adapted to their environment. The objective of Chapter 2 is to compare predicted and observed mean fitness of C. fasciculata in a natural selective environment. Observed mean fitness of both second-generation cohorts was, however, lower than predicted by the FTNS and lower than their respective first-generation cohorts. However, comparison of first and second-generation cohorts growing in the same year and, hence, common conditions, demonstrated an increase in mean fitness. Thus, environmental differences between years, as well as genotype-by-environment interaction, contribute to the deviation of observed from predicted mean fitness. In Chapter 3, I performed a quantitative genetic study of phenotypic selection on C. fasciculata to examine the effect of selection and environment on the phenology of germination and reproductive initiation. In this population, selection for advancement in reproductive stage was detected, as well as a response of 2.2 days earlier flowering in the second generation. Overall, findings of these chapters present a population that has demonstrated a response to selection in flowering phenology and significant genetic variation for evolutionary fitness. This evidence of adaptation and substantial adaptive capacity conveys crucial information regarding the likelihood of population persistence, information that could be utilized for other species towards conservation goals.