Lecture 26 - Hominid Evolution

Lecture 26 - Hominid Evolution

1. Evidence

   • Hominini fossil records (including the Homo genus) are extremely poor because hominins don't preserve in most environments.
     • Except for...
       • A) Caves
         • E.g. Cheddar Man, Somerset: skeletons discovered ~2000 with signs of cannibalism.
       • B) Highly calcareous sediments
         • E.g. H. heidelbergensis, West Sussex: found in alkaline chalk originating from 500 ka.
       • C) Peat bogs
         • E.g. Lindow Man, Cheshire: originating from 200 AD as a human sacrifice.
   • aDNA
     • Is extracted from well preserved fossils in order to transform poor fossil records.
     • aDNA and DNA are used to identify evolutionary family trees for Neanderthals and other hominin species as well as modern genetic lineages.
       • There is a genetic indication of an unknown hominin.
     • The Biomolecular Clock
       • Describes the idea that as the number of substitutions increases, the number of millions of years since a species diverged also increases.
         • Meaning you can use genetic similarity/difference to estimate when a species diverged.

2. Hominins split from apes 6-8 Ma

   • Hominin phylogeny is very controversial and ever-changing.
     • Phylogeny - the evolutionary history of a group of organisms (often represented as a phylogenetic tree).

3. Homo genus evolved in East Africa ~3 Ma

   • One minute before midnight if converted to 24 hours.
   • Evolution:
     • Australopithecus genus
       • Homo genus
       • Paranthropus genus (becoming extinct ~1.5 Ma)

4. Homo sapiens evolved from the H. heidelbergensis line

   • Two seconds before midnight if converted to 24 hours.
   • Evolution:
     • H. habilis
       • H. heidelbergensis
         • H. sapiens
         • H. neanderthalensis (widespread across Europe, becoming extinct 40 ka).

5. Five distinct hominin species were alive ~50 ka, but now only one remains

   • The Neanderthals, Denosovans, H. luzonensis and H. floresiensis are all now extinct.
     • As recently as 2019, H. luzonensis was discovered on Luzon island, The Philippines.
       • Evidence of interbreeding with H. sapiens.
     • Neanderthals went extinct in Europe ~40 ka when the last glaciation began.
       • There is evidence of Neanderthal cave art and shell jewellry (culture and art).
     • H. floresiensis are also known as "the Hobbit" because they are very short.

6. H. floresiensis has an earlier evolutionary pathway than the other four species

7. The East African Rift Valley

   • A tectonic rift pushing Africa apart (into 2 parts to the West and East).
     • Highly volcanic
     • Dynamic landscape
       • High habitat diversity, providing a range of niches to occupy.
     • Home to small habitat islands which fueled subspecies evolution, generating new hominin species.
   • Aka. "the cradle of humanity".
   • stimulated hominin radiation because of reasons linked to climate change and isolation of populations

8. The Out of Africa Hypothesis

   • H. sapiens evolved in the East African Rift Valley ~200 ka before migrating to all other continents (except Antarctica) after the Last Interglacial (125 ka).
     • Facilitated by lower sea level which exposed land bridges.