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In this chapter, we ask several simple questions. How many species are there, both named and unnamed? How fast are species now going extinct? How fast do species go extinct normally? And how fast do they diversify and thus might be able to recover from the current massive losses? Finally, where are extinctions concentrated, and how can we use this information to prevent extinctions?
This deceptively simple question has a rich – and even theological – pedigree. Westwood (1833) speculated ‘On the probable number of species of insects in the Creation’.
Humanity’s future will be shaped by the portfolio of capital assets we inherit and choose to pass on to our descendants, and by the balance we strike between the portfolio and the size of our population. So it makes sense to include population on the list of a society’s assets and build an overarching study of our relationship with our descendants and with nature by dividing assets into three categories: produced capital (buildings, roads, ports, machines, instruments), human capital (population, health, education, knowledge and skills) and natural capital (biodiversity, ecosystems, subsoil resources). In this Introduction we offer a perspective on the chapters that follow by summarising salient aspects of humanity’s troubled relationship with the biosphere.