Relevance of the eastern African coastal forest for early hominin biogeography
JCA Joordens, CS Feibel, HB Vonhof, AS Schulp & D Kroon 2019
JHE 131:176-202 open access

The influence of climate change on hominin evolution is much debated.
2 issues hamper our understanding of this process:
-the limited hominin fossil record,
-incomplete knowledge about hominin spatial occupation of Africa.

Here, we analyze the presently known hominin fossil distribution pattern,
we explore the potential geographic distribution of hominins between ∼4.5 & ∼2.5 Ma.
We assess the relevance of the Coastal Forest of Eastern Africa (CFEA) along the Indian Ocean as a core area for early hominin evolution.

Based on bio-phylo-geographic data, we propose the Coastal Refuge Hypothesis:
the CFEA provided a refugium for early hominins in periods of variable climate & strong seasonality during eccentricity maxima.
From this refuge, evolved spp could disperse inland (e.g. to rift basins) via vegetated humid corridors, whenever onset of stable climate periods with low seasonality during eccentricity minima allowed expansion out of the coastal enclave.

We develop a conceptual model in time & space, comparing predictions with climatic & hominin fossil records:

1) between ∼4.5 & 3 Ma,
ongoing (mostly anagenetic) hominin evolution occurred in the CFEA
+ inland dispersal events at ∼4.4, 4.2, 3.8, 3.5, 3.2 Ma,

2) before ∼3 Ma,
the Afar Basin was a (sub)core area often connected to & rel.similar to the CFEA
(other inland areas were +-marginal for early hominin habitation),

3) after ∼3 Ma,
Northern Hemisphere Glaciation exerted strong influence by causing latitudinal contraction of the CFEA, leading to
-habitat fragmentation,
-isolation of hominin populations &
-possible cladogenetic evolution.

A major challenge for the CRH is that at present, no (hominin) fossils are known from the CFEA.
We consider how this can be explained, and possibly overcome with targeted search efforts.

We discuss how the CRH can be
-tested (e.g. with molecular phylo-geography approaches),
-used to predict new hominin fossil locations.

With this study, we hope to contribute a fresh perspective to the climate-evolution debate, emphasizing the role of climatic stability, length of dry season & vegetation cover to facilitate connectivity between hominin core & marginal habitats.

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Coastal forest = aquarboreal.
"Core area": the littoral forest was the original hominoid environment, rather than a refuge?
see our 2002 TREE paper,
IMO this is not about human, but about hominid (Pan-Homo-Gorilla) or Homo-Pan evolution:

Joordens cs assume all African hominid fossils ("hominins" incl. australopiths) are more closely related to Homo than to Pan or Gorilla,
but this is an incorrect anthropocentric assumption:
google e.g. "two incredible logical mistakes 2019 verhaegen".

A more (bio)logical scenario IMO is this (cf our TREE Trends Ecol.Evol.paper):
-early hominoids +-18 Ma lived in coastal forests along the Tethys,
-hylobatids left Africa-Arabia, following the E-Tethys coasts (Ind.Ocean),
-pongids & hominids split +-15 Ma, somewhere along the Tethys (Anatolia??):
-pongids followed the E-Tethys coastal forests (Indian Ocean),
-hominids-dryopiths colonized the W-Tethys coasts/islands (Medit.Sea),
-after +-10 Ma, hominids (re)entered Africa (via shallow Lybian seas??),
-Gorilla & Homo-Pan split +-8 Ma:
-Gorilla remained in the Nile-Chad-Rift-Congo wetlands ->afarensis-boisei...
-Homo-Pan trekked to Joordens' CFEA, where H & P split +-5 Ma:
-Pan colonized S-African wetlands->africanus-robustus-naledi...
-Homo followed the Ind.Ocean coasts & islands ->H.erectus Java etc.

But we still don’t know:
-did the Gorilla/HP split happen at Kingdon's Line (African continent)?
-or in E-African coasts (cf Joordens cs 2019 JHE)?

In any case, Pan & Gorilla apparently evolved allopatrically in parallel in comparable environments,
I'd think (see my Hum.Evol.papers, and cf Jonathan Kingdon):
-Gorilla in the central forest wetlands Nile-Chad-Rift-Congo,
-Pan-Homo in the eastern coastal forest.