Reconstructed setting· The columns of time

The long walk

75 ka → 45 ka

A file of walkers heading for the horizon, a small craft at the water's edge, and a deliberately sparse landscape. This is the backdrop of the departure from Africa.

What the evidence shows

The sparseness is the argument. Genetic data record a substantial reduction in effective population size accompanying the expansion out of Africa, the mark a founder event leaves in a genome. The people who left were few, and the ancestry of everyone living outside Africa traces almost entirely to that small number. The craft is there because reaching Sahul meant crossing open water. The earliest known occupation on the far side is dated to around 65,000 years ago, an age other work contests and brings down to 50,000. The mangroves along the shore are not decoration either: they ring much of the Indian Ocean margin and may have drawn the route rather than blocked it.

Bounds and conventions

A single backdrop for a movement that took twenty millennia and crossed several climates. It shows the shore route because that is where the mangrove and Sahul evidence points; it does not rule out the others, and how many routes there were remains open.

Sources

1. Hallast, P. et al. (2020), Human Genetics, doi:10.1007/s00439-020-02204-9
2. Bergström, A., Stringer, C., Hajdinjak, M., Scerri, E. M. L., Skoglund, P. (2021), Nature, doi:10.1038/s41586-021-03244-5
3. Clarkson, C. et al. (2017), Nature, doi:10.1038/nature22968
4. O'Connell, J. F. et al. (2018), PNAS, doi:10.1073/pnas.1808385115
5. Gandini, F. et al. (2025), Science Advances, doi:10.1126/sciadv.ady9493
6. McEvoy, B. P. et al. (2011), Genome Research, doi:10.1101/gr.119636.110
7. Erlandson, J. M., Braje, T. J. (2015), Quaternary International, doi:10.1016/j.quaint.2015.03.046. Résumé lu ; le débat route côtière / routes intérieures y est explicite et repris dans la claim.