The human-caused biodiversity decline started much earlier than researchers used to believe. According to a new study the process was not started by our own species but by some of our ancestors.

The researchers point out in the study that the ongoing biological diversity crisis is not a new phenomenon, but represents an acceleration of a process that human ancestors began millions of years ago.

"The extinctions that we see in the fossils are often explained as the results of climatic changes but the changes in Africa within the last few million years were relative minor and our analyses show that climatic changes were not the main cause of the observed extinctions," explains Søren Faurby, researcher at Gothenburg University and the main author of the study.

"Our analyzes show that the best explanation for the extinction of carnivores in East Africa is instead that they are caused by direct competition for food with our extinct ancestors," adds Daniele Silvestro, computational biologist and co-author of the study.

Figure 3
Figure 3 - Predicted and observed temporal changes in the fraction of large carnivores (those with a body mass >21 kg). Median values across all 100 replicates are given, along with the full range across replicates. We also show the median predicted change, based on the climatic conditions outlined in Table 1. In order to focus on the predicted temporal change rather than the absolute predictions, we transformed the predictions to have the empirical slope but the same value at 4 Ma as the median from the fossil analyses. © Søren Faurby Daniele Silvestro Lars Werdelin Alexandre Antonelli

Søren Faurby, Daniele Silvestro, Lars Werdelin, Alexandre Antonelli. Brain expansion in early hominins predicts carnivore extinctions in East Africa. Ecology Letters, 2020

DOI: 10.1111/ele.13451

While the anthropogenic impact on ecosystems today is evident, it remains unclear if the detrimental effect of hominins on co‐occurring biodiversity is a recent phenomenon or has also been the pattern for earlier hominin species. We test this using the East African carnivore fossil record. We analyse the diversity of carnivores over the last four million years and investigate whether any decline is related to an increase in hominin cognitive capacity, vegetation changes or climatic changes. We find that extinction rates in large carnivores correlate with increased hominin brain size and with vegetation changes, but not with precipitation or temperature changes. While temporal analyses cannot distinguish between the effects of vegetation changes and hominins, we show through spatial analyses of contemporary carnivores in Africa that only hominin causation is plausible. Our results suggest that substantial anthropogenic influence on biodiversity started millions of years earlier than currently assumed.

Keywords: anthropogenic, bayesian, carnivora, humans, pleistocene, pliocene PyRate
Figure 1
Figure 1 - Potential drivers of carnivore extinctions in East Africa. (a and b) Extinction rates (expected number of extinction events per lineage per million years) through time, as inferred from the best‐fitting Bayesian model (Table S1) for small carnivores (i.e. a constant extinction rate model) and large carnivores (i.e. a model with linear correlation between extinction rates and brain volume). Dark lines show mean posterior rates inferred from 100 replicated analyses, where all fossils in each analysis are assigned a random age between the minimum and maximum age of the fossil site, and shaded areas indicate 95% credible intervals around rates. Horizontal bars above the time axis show the boundary between the Pliocene and the Pleistocene. (c–g) Potential predictors of the extinction patterns. (c) Mean annual temperature (Fortelius et al. 2016). (d) Mean annual precipitation (Fortelius et al. 2016). (e) Fraction of forest cover (Cerling et al. 2011). (f) Annual water deficit (Blumenthal et al. 2017). For (c–f) The raw data are depicted as circles with horizontal bars showing the dating uncertainties around each measurement. (g) Evolution of brain volume in hominins (White et al. 2009; Seymour et al. 2016). Diamonds, squares and circles indicate fossil measurements for species of Ardipithecus, Australopithecus, and Homo, respectively, with horizontal bars showing temporal uncertainties. In c–g, points were interpolated by computing the median of 1000 loess regressions obtained after resampling the dates of each measurement to incorporate temporal uncertainties. (h) Fossil sites. These analyses indicate that extinction rates in large carnivores (> 21 kg) are best explained by changes in hominin brain size or forest cover. In contrast, there is no evidence of rate variation in small carnivores, as would be expected in climate‐driven extinctions. © Søren Faurby Daniele Silvestro Lars Werdelin Alexandre Antonelli