What is the origin of the human species?

Latest revision as of 04:20, 1 May 2025

Written by AI. Help improve this answer by adding to the sources section. When the sources section is updated this article will regenerate.

Summary

The best-supported view in 2025 is that Homo sapiens evolved within Africa from a metapopulation that was already geographically and genetically structured. Over hundreds of thousands of years these African lineages exchanged genes, producing the ancestral diversity shared by all living people today [1]. A subset of these Africans expanded into Eurasia roughly 60–70 kya, where additional, limited gene flow occurred with other hominins such as Neanderthals.

Key points from recent research

Deep structure inside Africa.

A new structured-coalescent model that fits whole-genome data from people on every inhabited continent shows that the ancestors of modern humans were subdivided for at least 1 million years before the most recent common ancestry of today’s populations [1]. Rather than a single “cradle,” the model supports several long-standing, semi-isolated populations linked by intermittent gene flow.

Out-of-Africa remains robust.

Even with deep African structure, all non-African genomes still trace back to an expansion out of Africa within the last 100 kya [1]. This agrees with earlier genetic, palaeo-anthropological and archaeological evidence.

Adaptive fine-tuning after the expansion.

A 2024 ancient-DNA meta-analysis reports “pervasive directional selection” in traits tied to diet, immunity and climate adaptation after humans left Africa and settled new environments [3]. This indicates that the species’ origin predates (and is conceptually distinct from) later local adaptations.

Public discourse and open questions

Razib Khan describes the current picture as “complicated,” noting that the simple “single-origin, single-migration” story has been replaced by a model of “many Africas” and multiple pulses of expansion, contraction and introgression [2]. He emphasises that most researchers now see no contradiction between deep population structure inside Africa and the reality that all living humans are part of one species.

Palaeo-environmental studies highlighted in popular coverage of recent fieldwork underscore how climate shifts—such as the greening and drying of Arabian corridors—created windows that allowed small groups to leave Africa repeatedly [4]. Whether earlier forays left genetic traces, or were completely replaced by the later successful expansion, remains under debate.

Points of agreement

All living humans share most of their ancestry with African Homo sapiens that existed ≥300 kya [1][2].
A later expansion out of Africa populated the rest of the world and contributed the majority of ancestry outside the continent [1].
Subsequent gene flow with archaic hominins was real but limited; it does not challenge the African origin of our species [2].

Points of contention

How many semi-independent populations made up the ancestral African metapopulation, and where they were located [1][2].
Whether earlier “failed” dispersals left any surviving genetic legacy outside Africa [2][4].
The exact timing of the speciation process: some place the morphological roots of Homo sapiens >300 kya, while others propose a more recent genetic definition [1][2].

Consensus view

In sum, Homo sapiens is an African species that emerged from a long-lived, structured set of populations inside the continent. The single most successful out-of-Africa expansion about 60–70 kya spread those African genomes worldwide, after which local adaptations and limited archaic introgression shaped present-day diversity [1][3].

Sources[edit]

A structured coalescent model reveals deep ancestral structure shared by all modern humans – Nature Genetics (2025 peer-reviewed research article)
Current Status: It’s Complicated – Razib Khan’s Unsupervised Learning (2023 newsletter essay / Blog commentary)
Pervasive findings of directional selection realize the promise of ancient DNA to elucidate human adaptation – bioRxiv (2024 pre-print; Empirical research)
https://phys.org/news/2023-10-path-early-human-migrations-once-lush.html

Question[edit]

What is the origin of the human species?

@@ Line 1: / Line 1: @@
 ''Written by AI. Help improve this answer by adding to the sources section. When the sources section is updated this article will regenerate.''
-'''Short answer'''
+'''Summary'''
-Current genetic evidence places the deepest roots of Homo sapiens inside Africa.  Anatomically modern humans arose within a network of long-standing, semi-isolated African sub-populations that occasionally exchanged genes; one branch of this “structured metapopulation” later expanded out of Africa ~60–70 kya and peopled the rest of the world [1][2]. Subsequent gene flow with now-extinct Eurasian groups (e.g., Neanderthals, Denisovans) and strong directional selection in many environments further shaped regional genomes without overturning the African origin [3].
+The best-supported view in 2025 is that Homo sapiens evolved within Africa from a metapopulation that was already geographically and genetically structured. Over hundreds of thousands of years these African lineages exchanged genes, producing the ancestral diversity shared by all living people today [1]. A subset of these Africans expanded into Eurasia roughly 60–70 kya, where additional, limited gene flow occurred with other hominins such as Neanderthals.
-----
+'''Key points from recent research'''
-'''What recent studies show'''
+* Deep structure inside Africa.
+A new structured-coalescent model that fits whole-genome data from people on every inhabited continent shows that the ancestors of modern humans were subdivided for at least 1 million years before the most recent common ancestry of today’s populations [1]. Rather than a single “cradle,” the model supports several long-standing, semi-isolated populations linked by intermittent gene flow.
-* A 2025 structured-coalescent analysis that fits hundreds of modern and ancient genomes to complex demographic models finds that all present-day humans descend from a pan-African ancestral pool that already contained deep lineages >1 million years old.  These lineages remained partially isolated but never speciated, so the species boundary is shared by all modern humans [1].
+* Out-of-Africa remains robust.
+Even with deep African structure, all non-African genomes still trace back to an expansion out of Africa within the last 100 kya [1]. This agrees with earlier genetic, palaeo-anthropological and archaeological evidence.
-* A 2024 ancient-DNA meta-analysis reports dozens of loci where directional selection acted after the out-of-Africa expansion, confirming that much of the phenotypic divergence among living populations is recent and adaptive rather than reflecting separate origins [3].
+* Adaptive fine-tuning after the expansion.
+A 2024 ancient-DNA meta-analysis reports “pervasive directional selection” in traits tied to diet, immunity and climate adaptation after humans left Africa and settled new environments [3]. This indicates that the species’ origin predates (and is conceptually distinct from) later local adaptations.
-* A 2023 synthesis aimed at a lay audience emphasizes that the classic “single-origin” versus “multiregional” debate is now obsolete; instead, researchers speak of a “complicated” pan-African origin with later admixture from archaic hominins outside Africa [2].
+'''Public discourse and open questions'''
-----
+Razib Khan describes the current picture as “complicated,” noting that the simple “single-origin, single-migration” story has been replaced by a model of “many Africas” and multiple pulses of expansion, contraction and introgression [2]. He emphasises that most researchers now see no contradiction between deep population structure inside Africa and the reality that all living humans are part of one species.
-'''Areas of agreement'''
+Palaeo-environmental studies highlighted in popular coverage of recent fieldwork underscore how climate shifts—such as the greening and drying of Arabian corridors—created windows that allowed small groups to leave Africa repeatedly [4]. Whether earlier forays left genetic traces, or were completely replaced by the later successful expansion, remains under debate.
-* Africa is the geographic cradle of our species [1][2].
+'''Points of agreement'''
-* Modern non-Africans trace most of their ancestry to a single (or closely related) population that left Africa late in the Pleistocene [1][2][3].
+* All living humans share most of their ancestry with African Homo sapiens that existed ≥300 kya [1][2].
+* A later expansion out of Africa populated the rest of the world and contributed the majority of ancestry outside the continent [1].
+* Subsequent gene flow with archaic hominins was real but limited; it does not challenge the African origin of our species [2].
-* Limited gene flow occurred between that expanding population and Eurasian archaic humans, adding ≤10 % of the genome in some regions but not replacing the African foundation [3].
+'''Points of contention'''
-----
+* How many semi-independent populations made up the ancestral African metapopulation, and where they were located [1][2].
+* Whether earlier “failed” dispersals left any surviving genetic legacy outside Africa [2][4].
+* The exact timing of the speciation process: some place the morphological roots of Homo sapiens >300 kya, while others propose a more recent genetic definition [1][2].
-'''Ongoing debates'''
+'''Consensus view'''
-# How old is Homo sapiens?
+In sum, Homo sapiens is an African species that emerged from a long-lived, structured set of populations inside the continent. The single most successful out-of-Africa expansion about 60–70 kya spread those African genomes worldwide, after which local adaptations and limited archaic introgression shaped present-day diversity [1][3].
-   The structured-coalescent model places the deepest splits among African lineages at 1–1.2 Ma, older than many fossils typically labeled sapiens [1]. Critics worry that such estimates blur the line between species and population.
-# How fine-grained was the ancestral structure?
-   Some scholars prefer a few large “stem” populations, others a lattice of many local demes.  The 2025 study supports multiple enduring lineages, whereas Razib Khan’s essay underscores the uncertainty and cautions against overfitting sparse data [2].
-# Did any non-African archaic population contribute substantially more than the known Neanderthal/Denisovan fractions?
-   So far, ancient-DNA scans recover only small additional signals [3]; however, hidden “ghost” introgression inside Africa remains plausible, and future data may revise estimates.
-----
-'''Timeline of the public discourse'''
-* 19th c. – Darwin and Huxley argue for an African origin based on great-ape affinities (widely debated).
-* 1987 – “Mitochondrial Eve” paper popularizes a recent African origin model (no citation in sources; background context).
-* 1990s – Multiregional advocates propose regional continuity outside Africa.
-* 2010 – Draft Neanderthal genome proves interbreeding with modern humans.
-* 2020–2023 – Surge of African fossil discoveries and whole-genome studies shift consensus toward a pan-African, structured model; Razib Khan summarizes the new “it’s complicated” mood [2].
-* 2024 – Large ancient-DNA survey quantifies post-dispersal selection, reinforcing a single-origin framework with later adaptation [3].
-* 2025 – Nature Genetics structured-coalescent paper formalizes the deep, shared African ancestry of all humans and becomes a touchstone for the current synthesis [1].
-----
-'''Current consensus snapshot (2025)'''
-# Homo sapiens evolved in Africa within a dynamically structured metapopulation.
-# One branch left Africa late in the Pleistocene, after which regional selection and limited archaic introgression diversified global populations.
-# All living humans remain part of a single, recently diversified species with shared origins and considerable gene flow.
-----
-'''Why the answer keeps changing'''
-* Each new fossil or genome adds resolution but also complexity.
-* Statistical methods (e.g., structured-coalescent modelling) can now test more intricate scenarios than the simple bifurcating trees of the 1990s.
-* Public debate often lags behind technical advances, so terms such as “Out of Africa” or “multiregional” persist even when specialists have moved on to hybrid models [2].
-Contributors are encouraged to update this article as additional peer-reviewed data or high-quality preprints appear.
 == Sources ==