About 1.8 million species have been described since 1758. According to the authoritative IUCN Red List of Threatened Species between 88 and 100% of known mammals, birds, and amphibians, 44% of known reptiles, and 38% of known fish species have been evaluated. In total 5,488 or 22% of the world's mammals and 20% of fresh water fish are classified as threatened or extinct.1 Their status is a good indicator of the general health and well-being of the broader terrestrial ecosystem. Accordingly, this map is based exclusively on threatened terrestrial mammal distribution data plotted through individual species' biological ranges. By overlapping these ranges, a heat map of a world in the midst of the 6th extinction emerges.
The fact that we are in the midst of the 6th major extinction event in the history of life on earth is ascertained by the comparative measuring of the rate of extinctions against the background rate i.e., the normal rate of 'naturally occurring' extinction. 2 For example, in a recent study the background extinction rate estimated for mammals was conservatively set at two extinctions per 100 years per 10,000 species, whereas the current extinction rate is in the order of 100 times that. 3 Put another way, the total number of vertebrate species that went extinct in the last 100 years would, under normal circumstances, have taken about 800 to 10,000 years to disappear.
Such a rate has not been experienced since the asteroid induced demise of the dinosaurs some 65 million years ago. Paradoxically, it is to that random event that our own evolutionary lineage can be traced. The important difference between that 5th and the 6th extinction event is that human impact is not a sudden event from which life can immediately begin its recovery, a process variously thought to take between 10 and 30 million years to reach pre-extinction event levels of biodiversity.
Since we will remain in a dominant ecological position for the foreseeable future we will therefore determine the fate of many of the 8.7 million or so different species who, largely unbeknownst to us, share the world. That humanity has become self-aware and is evidently aggrieved by its role as evolution's executioner, suggests that the 6th extinction event is not entirely inevitable. On the contrary, life's munificence could be nurtured by humanity — itself like all species, destined to become extinct or morph into something else within a million years or so.
2 Gerardo Ceballos, et al., "Accelerated modern human-induced species losses: Entering the sixth mass extinction," Science Advances 1, no.5 (2015): e1400253.
1. Threatened Mammal Ranges
The IUCN Red List of Threatened Species™, Red List Spatial Data "Mammals" Version 4, http://www.iucnredlist.org/technical-documents/spatial-data (accessed November 12, 2014).
Critical Ecosystem Partnership Fund, "The Biodiversity Hotspots," http://www.cepf.net/resources/hotspots/pages/default.aspx (accessed July 1, 2014). Data made available under the Creative Commons BY-SA 4.0 License: https://creativecommons.org/licenses/by-sa/4.0/legalcode.