Zoos and Aquariums (AZA) population, 15% of the surveyed population displayed hair-plucking behavior with 62% of all institutions housing a hair-plucker. Individual gorillas, particularly those of a more solitary nature, are more likely to self-pluck using their fingers and pick up this behavior if they were exposed to a group member that plucked their hair as a youngster and not yet mature gorilla. Recent research on captive gorilla welfare emphasizes a need to shift to individual assessments instead of a one-size-fits-all group approach to understanding how welfare increases or decreases based on a variety of factors. Individual characteristics such as age, sex, personality and individual histories are essential in understanding that stressors will affect each individual gorilla and their welfare differently. Genetics The gorilla became the next-to-last great ape genus to have its genome sequenced. This was done in 2012. This has given scientists further insight into the evolution and origin of humans. Despite the chimpanzees being the closest extant relatives of humans, 15% of the human genome was found to be more like that of the gorilla. In addition, 30% of the gorilla genome "is closer to human or chimpanzee than the latter are to each other; this is rarer around coding genes, indicating pervasive selection throughout great ape evolution, and has functional consequences in gene expression". Analysis of the gorilla genome has cast doubt on the idea that the rapid evolution of hearing genes gave rise to language in humans, as it also occurred in gorillas. Furthermore, in 2013, a study was conducted in order to better understand the genetic variation in gorillas by using reduced representation sequencing. This study consisted of a sample of 12 western lowland gorillas and two eastern lowland gorillas, all in captivity. The study found that western lowland gorillas are more likely to be heterozygous than homozygous. Most pure (meaning they are not inbred) western lowland gorillas have a hom/het ratio that ranges from 0.5 to 0.7. Therefore, because of variation in these gorillas, it has been concluded that they display a moderate substructure within the western lowland population in general. Finally, the study sought out to analyze the allele frequency spectrum (AFS) in western lowland gorillas. The reason why is that AFS knowledge can help give information regarding demographics and evolutionary processes. The AFS has determined that western lowland gorillas display a deficit of rare alleles. Disease Western lowland gorillas are believed