For decades, rhinos were high on the kill list. Their imposing horn was in great demand, both as a hunting trophy and as an ingredient in traditional Asian medicine. Researchers have now found that intensive hunting has not only decimated the population, but also changed the animals' appearance: the horns of all five rhino species have become smaller and smaller over time.
Rhinos are an endangered species, although some species are slowly recovering. Today, images of western hunters proudly posing in front of a slain animal appear outdated. However, intensive hunting of rhinos continued into the 1950s. And poaching still occurs today because the horns continue to fetch high prices on the black market. However, the horns have changed over time, as scientists have now found out.
Photos as a look into the past
A team led by Oscar Wilson, who was working at the University of Cambridge at the time of the research, investigated how relentless rhino hunting affected the animals' horn length. To do this, he and his colleagues analyzed photos of 80 rhinos taken between 1886 and 2018. They show representatives of all five rhino species - white rhino, black rhino, Indian rhino, Javan rhino and Sumatran rhino - each from a side view.
Based on the images, the scientists were able to subsequently determine the horn length of the animals in relation to their body size and thus find out how it had changed over time. In addition, they analyzed how the animals were portrayed in the images, such as menacing monsters or peacefully grazing giants. To do this, they not only looked at the 80 photographs, but also at drawings of rhinos that go back up to 500 years.
Shorter horns pose new dangers
The result: The horns of all considered species have shrunk over the last century - not significantly, but still significantly enough to be considered meaningful. The authors suspect that behind the shrinking of the horns lies a typical evolutionary mechanism, directed selection. Because large-horned rhinos in particular were profitable and lost their lives, "preferential hunting selection resulted in individuals with smaller traits surviving and breeding more, and passing those traits on to future generations, leading to an evolutionary shift," they explain Scientist.
Such directed selection had already been demonstrated in other animals such as elephants, but now also in rhinos for the first time. However, the smaller horns could also be disadvantageous for the animals, as the authors suspect: "Considering the diverse functions of rhino horns, it is likely that a decreasing horn length could have an adverse effect on defense or reproduction. Decreasing horn size may also increase poaching pressures on rhino populations, as more rhinos must be killed to meet demand for horn, which remains high.”
But Wilson and his colleagues have also made positive discoveries, at least as far as the depiction of rhinos in photographs and drawings is concerned. Before 1950, two types of representations predominated: on the one hand, photos with hunters proudly posing with the animals they had killed, and on the other hand, those that depict rhinos as fearsome animals that hunt people. According to the researchers, the second can be seen as an attempt to justify hunting rhinos. After 1950, however, the focus increasingly shifted to photographs and drawings depicting rhinos as peaceful creatures worthy of protection. According to the authors, the fact that this reversal took place in 1950 of all times has to do with geopolitical changes: the African countries have become independent and as a result no longer give European hunters such easy access to potential trophies.
Source: University of Cambridge; Specialist article: People and Nature, doi: 10.1002/pan3.10406