How old is our species, and what does our DNA remember?
Evidence The oldest fossils currently assigned to our lineage come from Jebel Irhoud, Morocco: 315,000 ± 34,000 years old. Evidence People with ancestry outside Africa carry roughly 1.5–2% Neanderthal DNA, and some populations also carry DNA from Denisovans. Interpretation The picture is a mostly African origin with limited interbreeding: a messy family history, with no sign of a sudden break.
The evidence
"…a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology."Evidence Hublin et al., Nature 546 (2017) · doi. Date: Richter et al., Nature 546 (2017) · doi
"…we now estimate that the proportion of Neandertal-derived DNA in people outside Africa is 1.5–2.1%."Evidence Prüfer et al., Nature 505 (2014) · doi (the 2010 draft genome estimated 1–4%: Green et al.)
"…interbreeding, albeit of low magnitude, occurred among many hominin groups in the Late Pleistocene."EvidenceInterpretation Prüfer et al. 2014
Evidence Denisovans were discovered from DNA in a finger bone (Reich et al. 2010). A Denisovan jaw at least 160,000 years old was later found on the Tibetan Plateau (Chen et al. 2019). Evidence Africans also carry some Neanderthal-derived DNA, from later back-migration (Chen et al. 2020).
Out of Africa vs multiregional
Interpretation The draft Neanderthal genome "presents a challenge to the simplest version of an 'out-of-Africa' model," but "the vast majority of genetic variants… outside Africa came from Africa" (Green et al. 2010). Multiregional theorists (Wolpoff et al. 2000) emphasize the gene flow. Unverified We haven't yet read their full argument.
How sure are the dates?
Evidence DNA "clocks" depend on the mutation rate. Direct measurements found a rate "approximately half" the older estimate, which stretches many dates (Scally & Durbin 2012). Fossil dates come from separate methods (thermoluminescence, uranium series), with their own error bars.
What would change our view
A fully modern skull much older than Irhoud outside Africa, a living population with majority archaic ancestry, or an abrupt, unexplained break in the genome at our origin.
Help us check this
Questions from our dossiers. These are open problems in our research that we haven't solved. If you can answer one, it may change this note, our videos and future episodes. Votes can choose which question we chase next, but only evidence decides the answer.
- E1 · Is Jebel Irhoud "us"? Send a peer-reviewed paper arguing that the Irhoud fossils are not Homo sapiens. We'll lay out both sides. Send: paper + DOI. Status: open
- E2 · Denisovan ancestry today. What is the best current (post-2016) estimate of Denisovan ancestry in Papuans and Aboriginal Australians? Send: paper + DOI. Status: open
- E3 · Molecular clocks. Name one human-evolution date that moved substantially when the mutation rate was revised. Send: the before and after papers. Status: open
- E4 · Neanderthal DNA in Africa. Has Chen et al. 2020's finding been replicated or challenged? Send: the follow-up paper + DOI. Status: open
- E5 · Sitchin's date. Where exactly does Sitchin date the creation of humans? Help us quote him accurately before we compare him with the fossils. Send: book, edition, page. Status: open
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