Counting what is alive

The order, and why it is this one

Join anywhere. Each stop carries the route with it, so the foot of every question here offers the next one and the way back to this page.

1. 01How many living things have we never met?About 2.4 million species of animals, plants, fungi and other eukaryotes had been formally described by August 2026. Estimates of how many exist range from under 10 million to numbers that make the word “species” difficult to apply at all.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
2. 02What is a species?More than twenty definitions of species are in use, and they disagree about real cases. A 2007 proposal reconciles most of them by separating what a species is from how one is recognised, which clarifies the disagreement without eliminating it.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
3. 03Why are there more species in the tropics?Species richness rises towards the equator in almost every group on land and at sea. The pattern is among the most robust in biology and among the least explained: the leading accounts differ on whether the tropics make new species faster, lose them more slowly, or have simply had longer.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
4. 04Is this a mass extinction?Documented extinctions since 1500 are far fewer than in the five great mass extinctions. Measured as a rate against the background from the fossil record, vertebrate losses over the last century are up to a hundred times higher, and the comparison depends on assumptions that are stated openly and argued about.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
5. 05Can an extinct species be brought back?Ancient DNA can be sequenced, but a sequence is not a working genome, and no mammoth cell exists to clone. What is feasible is editing a close relative’s genome towards an extinct one, which produces a hybrid with some of the traits and none of the lineage.Shallowsdepth, meaning: Interesting questions with substantial evidence and real uncertainty remaining.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read