Reality → Life → Evolution → Biodiversity
About 2 million living multicellular species have been identified so far. Biologists estimate that millions more (mainly invertebrates) will be identified in future and that maybe 100 times as many went extinct in the past [1] . Presently known species include:
In addition, fungi, bacteria and archaea harbor an untold number of 'species' [2] . Ecosystems provide food chains and waste recycling in highly complex webs of interactions by species, populations, and individuals with the environment [3] . Industrialization in the 18th century triggered explosive growth of human population [4] with a threatening outlook for our planet's future ecology.
The profusion of life forms is often illustrated in the 'tree of life'. Molecular genetics and genomics suggest new possible species and ancestral linkages that are described in cladograms, where a clade represents a group that includes a common ancestor and all its descendants (an interesting study case is the order of egg-laying mammals, popularly represented by the Australian Platypus).
Ecosystems change geographically and over time. Major determinants are climate, water availability, and naturally established food chains marked by competition, predation, parasitism, and symbiosis of species adapted to the environment. Human intervention dramatically changes natural evolutionary processes, with 'bad' and 'good' but ultimately unknown evolutionary effects.
World human population before the invention of agriculture (some 10-15 thousand years ago) probably never exceeded 15 million. Based on European and Asian records, world population in medieval ages might have been about 400 million. Only with the impact of industrialization about 200 years ago (0.01% of homo sapiens' era) exponential growth started, escalating world population to presently 7 billion, i.e., a doubling every 50 years.