For more than a century, explorers and settlers have warned about the likely impact of the hunting of lions and other wild animals in Africa. One of the most prescient, Frederick Selous, the inspiration for the character Allan Quatermain in the novels of H Rider Haggard, wrote in 1908 that “since my first arrival in 1871, I had seen game of all kinds gradually decrease and dwindle in numbers to such an extent that I thought that nowhere south of the Great Lakes could there be a corner of Africa left where the wild animals had not been very much thinned out”.

Now researchers have uncovered the impact of that predation on the lion. Lion numbers and range have plunged – but it appears their genetic fitness has also declined. An alarming new study has revealed that lions shot by colonial hunters more than 100 years ago were more genetically diverse than the ones that now populate Africa. The discovery is worrying because it indicates that the species’ fight to survive may be even more difficult than had been previously thought.

“Loss of genetic diversity means that lions are now less able to withstand new diseases or environmental problems, such as heatwaves or droughts,” said lead author Simon Dures, of the Zoological Society of London. “It means that we will have to be even more careful about how we try to protect them.”

Increased parcelling of land by farmers makes it harder for lions to interact, further reducing their genetic diversity

In the late 19th century there were about 200,000 members of Panthera leo roaming the savannahs of Africa. Then European colonialists arrived and began shooting lions – the most social of all cats – in their thousands, first as sport and later to protect the cattle that the newcomers had begun to farm. With fewer than 20,000 of these majestic predators left on the continent, the species has now been designated as “vulnerable”.

“We knew there had been major reductions in numbers of lions,” said Dures. “However, we did not know how badly the survivors had fared genetically.”

To provide answers, the team used two sources of lion DNA. The first came from samples taken from wild lions in the Kavango-Zambezi conservation area, a vast region – roughly the size of Britain – that stretches over parts of Botswana, Namibia, Zambia and Zimbabwe. It is one of the largest areas left in Africa where lions can live relatively undisturbed.

A lion shot during a hunt in 1910. Hunting and habitat pressure have both contributed to the decline in the cats’ genetic strength. Photograph: Bettmann Archive

The other source of DNA was provided from samples of skin and bone taken from specimens kept at the Natural History Museum. These lions had been killed and sent to the museum by explorers and hunters between 1879 and 1935.

DNA was extracted from both sets by the researchers from Britain, Botswana, South Africa and Namibia – and compared. “What we found was striking,” said Dures. “The genetic diversity of the modern population of lions had been reduced by about 15%.” When it comes to DNA, a lion’s share is not what it used to be, in other words.

That has important repercussions. With a high genetic diversity, a population of any animal possesses a wider selection of different versions of genes than a population with low genetic diversity. It is then better able to cope with environmental changes, diseases and other threats. The new research has shown that lions have lost some of that ability over the past 100 years and suggests that hunting, and habitat pressure, were involved.

And that is an important discovery. Climate change threatens to trigger new diseases among African wildlife and to bring about more intense droughts and heatwaves. With reduced genetic diversity, lions will be further threatened. In addition, increased parcelling of land by farmers is making it more and more difficult for lions to move and interact, further reducing their genetic diversity.

“It is a modern problem, but the warning signs have been around for a long time, as Selous made clear,” added Dures.