How many animal species have humans driven to extinction?

The impact we, as humans, have had on wildlife and the extinction of numerous animal species is irrefutable. From the infamous dodo bird and golden toads to the iconic Tasmanian tiger, our actions have contributed to the demise of these unique creatures. However, the exact number of animal species driven to extinction by humans is a challenging figure to estimate. Nonetheless, it could be in the range of hundreds of thousands.

To begin, let's consider the confirmed extinctions. According to the International Union for Conservation of Nature (IUCN) Red List, a total of 777 animal species have gone extinct since the dawn of the modern era in 1500. While some of these extinctions might have occurred naturally, the influence of human activities remains evident considering our significant impact on nature, especially within the last 500 years. It's important to note that humans have been contributing to extinctions for thousands of years, though scientific study of those events was not possible. For the purposes of this discussion, we will focus on the approximate timeframe of the past 500 years due to uncertainties surrounding current extinction rates.

It's worth mentioning that only around 5% of the world's known species have been assessed for extinction risk by the IUCN. This implies that there are potentially numerous unrecorded extinctions. A study published in 2022 in the journal Biological Reviews suggested that the number of all known species that might have perished since around 1500 could be as high as 150,000 to 260,000.

These staggering figures, which surprised the study's lead author, Robert Cowie from the University of Hawaii, come with certain limitations and caveats. Cowie's team calculated these estimates by examining a random sample of 200 land snails. They determined the number of extinct snail species based on previous scientific research and expert consultation. They then extrapolated these findings to ascertain the extinction rates if all known species had experienced a similar fate over a period of 500 years consistently. The calculated extinction rate ranged from 150 to 260 extinctions per million species-years (E/MSY), implying 150 to 260 extinctions every year for every million species on Earth. Additionally, Cowie analyzed estimates for extinction rates among other groups of wildlife, such as amphibians and birds, which ranged from 10 to 243 E/MSY. However, a common value seems to center around 100 E/MSY, which Cowie deems a reasonable assessment.

Applying this average rate to Cowie's method suggests that around 100,000 of the approximately 2 million known species have gone extinct within the past 500 years. However, these calculations do not account for unknown animal species. Another study from 2011 published in the journal PLOS Biology estimated the total number of animal species to be roughly 7.7 million. Assuming an extinction rate of 100 E/MSY over 500 years – subtracting the 3,850 animals expected to naturally go extinct during that time with a background extinction rate of 1 E/MSY – a rough estimate of the number of animal extinctions caused by humans is 381,150. It is essential to treat this estimate with caution due to the uncertainties involved.

John Alroy, an associate professor at Macquarie University, argues that accurately calculating modern extinction rates is virtually impossible. Alroy emphasizes that researchers must first determine the number of species in existence, a task compounded by limited knowledge of the world's wildlife. This issue is particularly prevalent in understudied regions like the tropics, where much of the biodiversity resides. Compounded by insufficient information regarding insects, the largest animal group in terms of species diversity, compared to larger-animal groups like mammals and birds.

Despite the exact rate remaining elusive, it is evident that humans are exacerbating the extinction crisis, and the number of extinctions far surpasses the tally of 777 recorded on the IUCN Red List. Various studies have shown extinction rates to be significantly higher than the background natural rate. Consequently, the impact of human actions on Earth's biodiversity remains devastating, regardless of the specific numbers.

"It's still a lot, and it's still really bad," Cowie warns, regardless of whether the extinction rate is 100 E/MSY, 20 E/MSY, or 200 E/MSY.

Earlier, SSP told that new study suggested that ammonites that were not in decline prior to end-cretaceous extinction.