From nothing to a body

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 did life begin?Life appeared on Earth remarkably early, and we can reproduce several of the chemical steps that might have led to it. What we cannot do is explain how those steps joined into something that copies itself.Deepdepth, meaning: Major unanswered questions.Unknown. Humanity does not currently have a satisfactory answer.Read
2. 02What was the ancestor of everything alive?Comparing the genomes of living organisms lets us reconstruct features of a population that lived billions of years ago. The reconstruction is real, partial, and contested.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
3. 03Why did complex cells appear only once?Bacteria and archaea have been evolving for billions of years, and apart from one event they show no tendency to evolve greater complexity. The eukaryotic cell appears once, apparently through one cell taking another inside it. Whether that step is hard, and why, is an open question with one quantitative answer on the table and a quantitative challenge to it.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
4. 04Why is there sex?Sexual reproduction halves the rate at which genes are passed on and requires finding a partner, so it needs a large compensating advantage. Several candidates have theoretical and experimental support. Which one does the work, and whether any is sufficient, is unresolved.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
5. 05How does a cell know what to become?The genome does not contain a plan of the body. Pattern arises from cells reacting to each other and to chemical gradients, and a mathematical account of how uniform tissue produces regular structures was published in 1952 and matched to mouse limbs sixty years later.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read
6. 06Why do we age?The evolutionary account of why ageing exists turns on selection that weakens with age and on evolved limits to somatic maintenance, rather than on any programme. The molecular account of what ageing is has a catalogue of processes that change with age, and no agreement on which of them cause it.Deepdepth, meaning: Major unanswered questions.Uncertain. Meaningful scientific, historical or philosophical disagreement remains.Read