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Homo sapiens, the ancestors of present-day humans, were responsible for the extinction of megafauna, according to new research. Scientists have revealed that over the past 50,000 years, more than 150 of the world’s largest animal species were wiped out, leaving only bones and burrows behind.
The research highlighted that terrestrial megafauna in recent prehistory, specifically during the Late Pleistocene (129,000–11,700 years Before Present or BP) and Early to Middle Holocene (11,700–4,200 years BP), suffered widespread and severe extinctions.
These extinctions, scientists say, were driven by modern humans (Homo sapiens) who expanded across the planet during this period. The study established clear trends of megafauna species becoming extinct with the emergence of behaviourally modern Homo sapiens in Africa, their colonisation of other areas and subsequent cultural development.
“Final megafauna declines, as indicated by fungal spores or sedaDNA, always occur close to or after modern humans became present in the broader region,” the study, published in the journal Cambridge Prisms: Extinction noted.
The scientists considered climate change, diseases, the impact of celestial bodies and humans as potential causes of extinction. They analysed evidence on climate and vegetation data from the past 3 million years, body size dynamics of mammals across 66 million years and archaeological data on human expansion and lifestyle.
Their findings showed that previous climate changes, even over millions of years, had never caused such a massive and selective loss of megafauna as seen in the last 50,000 years.
The Late Pleistocene — 129,000-12,000 years ago — saw a fluctuating climate, which has been earlier suggested as a reason for megafauna extinctions. However, the climatic changes in this period were no different from those of the preceding million years. Earlier climatic changes, however severe, did not cause widespread and selective megafauna losses.
The evidence shows weak or no support for any major influence of climate on the late-quaternary extinctions. This is evident from both coarse-grained macroecological patterns and detailed spatial/temporal and mechanistic evidence, with much evidence directly contradicting a climatic cause.
“One important pattern that argues against a role for climate is that the megafauna extinctions were just as severe in climatically stable areas as in unstable areas,” Jens-Christian Svenning, the lead author told Down To Earth (DTE). Svenning is a professor and director of the Center for Ecological Dynamics in a Novel Biosphere at Aarhus University in Denmark.
However, the movement of Homo sapiens out of Africa around 100,000 years ago, which hadn’t occurred during previous glacial cycles, presented a distinct factor in extinction dynamics. Scientists found strong, cumulative evidence for direct and indirect pressures from modern humans that drove megafauna to extinction.
Svenning said, “Early modern humans were effective hunters of even the largest animal species and clearly had the ability to reduce the populations of large animals. These large animals were and are particularly vulnerable to overexploitation because they have long gestation periods, produce very few offspring at a time and take many years to reach sexual maturity”.
The researchers also observed that regions with less climatic change or with megafauna adapted to survive the new climate did not offer greater protection against human pressure.
Large mammals such as giant ground sloths, giant armadillos, bears, deer, camels and various gomphotheres became extinct following the colonisation of Europe and South America, they noted.
“Humans had started intensively colonising southern Eurasia and Australia by 50,000 years ago, which directly relates to the acceleration of extinctions of megafauna from those regions,” Ninad Mungi, one of the authors of the study, told DTE.
Only 11 of the 57 species of terrestrial megaherbivores — plant-eating mammals weighing over 1,000 kilogrammes — survived to the present day (post 1,000 AD), representing an extinction rate of 81 per cent. These survivors include three species of elephants, four species of rhinoceros, the common hippopotamus, giraffe and two bovines.
The authors conclude that functional megafauna restoration, known as trophic rewilding, can have positive impacts on biodiversity and ecosystem function. This is because most extant species have evolved in ecosystems that once contained rich megafauna.
In the Indian context, four species went extinct after Homo sapiens increased in numbers. These included two proboscideans (relatives of elephants), a hippopotamus, a zebra, an ostrich and aurochs (wild ancestor of the present domesticated cattle).
“The important point to note is that these megafauna had survived multiple ice age events within which they may have experienced population declines, but did not go extinct,” said Advait Jukar, lecturer of paleontology, Department of Geosciences, University of Arizona, told DTE. Jukar was not involved in the study.
Apart from hunting, changes in land use and increasing human populations put additional stress on these megafauna species, said Jukar. These factors likely restricted the size of their habitats, which in turn could have been reasons for slow-recovering species to eventually go extinct. He emphasised the importance of including humans as a causal factor for megafauna extinction.
Citing examples of the Indian rhinoceros, Jukar said the species’ range extended from Afghanistan to central and southern Indian sub-continent to Sri Lanka. “But today, rhinos are restricted to small populations in national parks, with Kaziranga National Park housing roughly two-thirds of the world’s population. Wild buffaloes and Gaur have managed to survive and co-exist, but more research is needed to understand how they managed to survive while other species did not,” he noted.
Mungi added that the harvest of large animals was part of many dominant ancient cultures across South Asia until very recently. Cultural shifts and the spread of non-violent values likely halted imminent extinctions. Nonetheless, he said, ongoing rampant land-use changes, the harvesting of wildlife driven by international markets and the loss of genetic diversity have recently brought many megafauna species, like the Asiatic lion, Sumatran and Javan rhinoceros and wild buffalo, close to the brink of extinction.
“Human-led extinctions are an ongoing process. In the past, cultural shifts prevented large-scale extirpations of many species. We need similar civilisational interventions to halt extinctions and mitigate them,” Mungi added.
