According to scientists, rhino horns have been reduced over the previous century due to human poaching.

Decades of hunting rhinos with the longest horns have left only those with shorter horns, which are now passing on their genes.

The findings, published in the journal People And Nature by specialists from Cambridge University, are based on a review of photographs of animals from the previous 140 years, including all five species of rhino: white, black, Indian, Javan, and Sumatran.

Dealing with images circumvented the problem of working with physical rhino horn specimens, which researchers are often not permitted to access for reasons of security.

Oscar Wilson, a former researcher in the University of Cambridge’s department of zoology and the report’s lead author, stated: ‘We were ecstatic to uncover photographic proof that rhino horns have become shorter through time.

Due to security issues, they are perhaps one of the most difficult subjects to research in natural history.

Mr. Wilson, who is currently located at the University of Helsinki in Finland, added: ‘Rhinos evolved their horns for a reason – various species utilize them in different ways, such as to assist grasp food or protect against predators – so we believe that smaller horns would be detrimental to their survival.’

The researchers assessed the horns of 80 rhinos photographed with their horns visible between 1886 and 2018.

The online repository The Rhino Resource Centre contains images of all five species of rhinoceros: white, black, Indian, Javan, and Sumatran.

They viewed photographs of hunter-killed rhinoceros, including a 1911 photograph of former U.S. President Theodore Roosevelt standing over a black rhino he had just killed.

The researchers also examined other rhino body parts so that the proportion of horn length to body size could be correctly determined.

The team examined rhino artwork spanning more than 500 years, during which time paintings were employed to keep track of species.

Before the 1950s, there was relatively little attempt to promote rhino conservation to the general population, as evidenced by the photos and artwork.

Mr. Wilson stated, “For at least a few decades, there has been a considerably greater emphasis on the conservation of rhinos, and this is reflected in the more recent photos depicting their preservation in sanctuaries or their struggle in the wild.”

Rhinoceros are an endangered species with fewer than 30,000 individuals remaining in the wild.

At the beginning of the 20th century, there were almost half a million.

Three species of rhinoceros — black, Javan, and Sumatran — are deemed to be in a state of critical endangerment.