There has been global concern regarding the effects of selective harvest on the size of horns and antlers. Many government agencies have imposed regulations on hunters based on the size of antlers or horns to protect young males. This has caused phenotypic and genetic decline in the horn size of one bighorn sheep (Ovis canadensis) population and concern about the decline of antler size in white-tailed deer (Odocoileus virginianus). In Texas, USA, there has been interest in selective harvesting to increase genetic potential for antler size of white-tailed deer based on the results of several studies of penned deer. Designed studies on effects of selective harvest on horn or antler size in ungulates are rare, especially studies with a control area. We conducted 20 years of experiments on the effects of selective harvest on antler size of white-tailed deer using 2 research sites in South Texas, USA, each with a control area. Our first experiment was on the King Ranch in southeastern South Texas, where our objective was to see if we could change the phenotypic size of antlers in a population as one of the prerequisites for evolution. We picked a selective harvest area and a nearby area with only incidental recreational harvest as a control, each of about 3,800 ha. There were no barriers to deer movement on or off the study areas. We harvested the treatment area for 6 years (1999-2004) and monitored 1 year post-harvest (2005). For the selective harvest treatment, we used Texas legal methods for hunters and harvested yearling males (1.5 years of age) with <6 antler points and older males with <= 8 antler points. We monitored antler size by age class each year with pre-harvest captures in both areas using a helicopter and net gun. We harvested 135 males in the treatment area and an additional 33 were harvested by recreational hunters. Eight of the recreational harvests met our criteria. During the study, we caught and aged deer, measured antlers, implanted a microchip for recognition of recaptures, and released 436 and 303 males in the treatment and control areas, respectively. Selectively harvested males had smaller antlers than captured males for 1.5- and 3.5-4.5-year-olds but not other ages. Despite an average 8.6% annual harvest rate, antlers of all ages did not differ from the beginning to the end of the study. We concluded that insufficient harvest rate, immigration and emigration of yearling males, and rainfall variation affecting recruitment contributed to our results. We used results of the King Ranch experiment to guide design of follow-up experiments on the Comanche Ranch in southwest South Texas. We used 3 existing game-fenced areas to prevent or restrict deer exchange. A control area of 20 km(2) was completely high-fenced, as was an intensively harvested area of 14 km(2). A third area with a moderate selective harvest treatment encompassed 73 km(2) and was 85% enclosed by high fence. Deer on all study sites were provided with a pelleted nutritional supplement, which a concurrent study on Comanche Ranch showed prevented density-dependent population dynamics. The intensive treatment had harvest criteria similar to the King Ranch experiment, targeting 1.5-year-olds with <6 antler points and 3.5-4.5-year-olds with <= 8 antler points. Males 2.5 years old were harvested if <8 points, as were >= 5.5-year-olds with a gross Boone and Crockett score (GBC) <145. For the moderate harvest treatment, we released all 1.5- and 2. 5-year-olds and harvested older males with the same criteria as for the intensive treatment. To increase harvest rate, instead of using hunters, we harvested males at capture if they met selective harvest criteria. Males with antlers larger than the selective harvest criteria were released. We monitored antler size through yearly captures by helicopter and net gun in each area. In addition to measuring antler size, we aged and weighed captured males and inserted a microchip at the base of an ear of those that were released. We applied selective harvest treatments for 7 years (2006-2012) and continued capturing for 6 years post-harvest (2013-2018) to monitor for any lag effects of treatments. We estimated adult sex ratios using annual surveys by helicopter. Our initial objective, like the King Ranch study, was to see if harvest treatments increased the population antler size as one of the prerequisites for evolution. We captured 6,675 males over the 13 years of the study, including 3,346 recaptures. During the treatment period, we selectively harvested 365 males in the intensive treatment and 878 males in the moderate treatment. Harvested males of all age classes averaged smaller antlers than released males. We estimated a 19% yearly harvest rate in the moderate treatment (no harvest of 1.5- and 2.5-year-olds) and 48% of all ages in the intensive treatment. During the treatment period, adult sex ratio increased from 2:1 to 5:1 (female:male) in the intensive treatment but did not change in the moderate treatment, despite a male population size decrease of 65%. There was a large female harvest by Comanche Ranch during the harvest period that influenced sex ratio results in the moderate treatment. The male population decreased 88% during the harvest period in the intensive area. At the end of the harvest period (2013), antler size was larger compared to control in the 3.5-4.5-year (+10.67 GBC) and >= 5.5-year (+8.87 GBC) age classes in the intensive treatment and the >= 5.5-year (+3.70 GBC) age class in the moderate treatment. However, there was little evidence of phenotypic change and thus no detectable trait evolution by the end of the post-harvest period (2018), as all ages averaged smaller antlers or did not differ compared to the control. Additionally, only the 3.5-4.5 age class in the moderate treatment had larger antlers in 2018, versus the study beginning in 2006. Males changed state across years from eligible for harvest to the do-not-harvest category according to our criteria, and vice versa, likely as a result of stochastic rainfall. We used the experimental design, capture data, and ear tissue from the Comanche Ranch experiment to conduct 3 genetic studies. First, we analyzed male breeding success using 15 microsatellite loci. Our objective was to determine if male breeding success by age class changed in the treatment areas versus the control site during the treatment period (2006-2012). We genotyped 162, 432, and 1,504 captured males in the control, intensive, and moderate areas, respectively. Mature males (>= 5.5 years of age) comprised most of the sires in the control (62%) and intensive areas (42%). However, young males (1.5-2.5 years old) outnumbered mature males in the moderate treatment by 40% versus 28%, respectively. We assigned sires for 650 of 938 (69%) sampled offspring (1.5 years of age). Successful males sired 1-6 male offspring/year. During the post-harvest period (2013-2018), mature males comprised most of the candidate sires in the control (81%) and moderate (40%) areas. In contrast, young males slightly outnumbered mature males, 39% versus 34% in the intensive treatment. During post-harvest, successful males sired 1-4 male offspring that were recruited and averaged 1.1, 1.8, and 1.5 offspring/year for the control, intensive, and moderate areas, respectively. The objectives of our second genetic study were to 1) estimate heritability for antler traits, the proportion of variation in a trait within a population that is attributable to genetic differences rather than environmental factors, by age class, and 2) whether Comanche Ranch selection differentials were sufficient to cause evolution in antler size. We constructed pedigrees based on paternity assignments and then used an animal model procedure to estimate variance components and heritability of antler traits. Estimated heritability (h(2)) for antler points and GBC was low (0.06-0.16) for males 1.5-2.5 years of age. For males >= 3.5 years of age, heritability for antler points ranged from 0.25-0.32, and for GBC ranged from 0.31-0.68. Repeatability for antler points and GBC score ranged from 54-58%. Our annual estimates for generation time across treatments and the control area ranged from 3.8-7.3 years. Estimated response to selection was <= 0.2 for antler points for all ages and 0.8-5.8 GBC units for males >= 3.5 years of age. Given the long generation times and modest predicted responses, if there were genetic changes due to our selective harvest treatments, they appeared to be minor in these high-fenced populations. Our third genetic study was to estimate if selective harvest for antler size at Comanche Ranch was correlated with the distribution of major histocompatibility complex (MHC) DRB II genotypes in sires and offspring. The MHC DRB complex is associated with the immune system in animals. Previous research in Oklahoma, USA, has shown a relationship between MHC DRB and antler size in white-tailed deer. For this study, we used tissue from captured males of known age that were born in 2011 and 2012. No association between MHC DRB II alleles and antler development was detected. We speculated that the semi-arid climate of South Texas may result in fewer pathogens than the more mesic climate of previous research. We concluded that selective harvest to alter gene frequencies at the population scale to increase antler size in white-tailed deer, if possible, would require decades and would be unlikely in open populations with dispersal and no supplemental feed. Our results also showed that antler size restrictions on harvest by governmental agencies would be unlikely to cause evolution in white-tailed deer.