Homo hobbit! “Flores man” & patterns of human evolution

What is EVOLUTION?  Heritable change in a population, over time. PATTERNS OF EVOLUTION  The various ways in which such change can develop.  This change may ultimately end in Reproductive/ Genetic isolation, and speciation.

Anagenesis = change within a population; Cladogenesis = branching (divergence) to produce 2 new species. 2 patterns of speciation:

2 modes of speciation

Allopatric speciation: populations are isolated by geographical barriers. No gene flow; speciation occurs through gradual microevolution e.g. adaptive radiation on island groups (kea & kaka, Placostylus in NZ); e.g. H. floresiensis. Most likely in small, isolated populations:  Founder effect limits size of gene pool;  Genetic drift has greater effects in small populations;  Different environment may generate different selection pressures.

The branched evolution of horses

Antevs/ecol438/lect18.html

Anagenesis (e.g. Pennisi 2006) Divergence

What drives such changes?

At the root of the tree: bipedalism

Sahelanthropus tchadensis – 6-7 mya

Virtual reconstruction of Sahelanthropus cranium (from Zollikofer et al. 2005)

Orrorin tugenensis - 6mya

“Lucy” – Australopithecus afarensis – c. 3.2 mya

The Laetoli footprints – c. 3.2 mya

What sort of natural selection pressure would drive the evolution of bipedalism?

Species A TIME Species B Evolutionary change How does this work ????? 1. Mutation (e.g. bipedalism) 2. Advantage (e.g. allows better cooling) 3. Better breeding success (e.g. bipeds have more offspring) 4. Increased % bipeds in population over time 5. Reproductive isolation (biped/quadruped hybrids infertile)

Adaptive Radiation: By divergent evolution Eg multiple Australopiths & Homo spp

Kenyanthropus platyops At least one other hominid species lived in Africa at the same time as A. afarensis:

Gracile australopithecines Australopithicus africanus 3 – 2.3 mya

Robust australopithecines Paranthropus robustus, boisei, aethiopicus (1.9 –1.5 mya, 2.3 – 1.4 mya, 2.8 – 2.3 mya)

Homo habilis (“handy man”)

Advances in cranial capacity What selection pressures would drive this? What selection pressures would act against it? apes

Pelvic inlet (the birth canal).

Homo erectus: found in Africa, Middle East, south & south-east Asia from 1.7mya to 200,000 years ago.

Homo neanderthalensis: Neanderthal man 200,000 – 30,000 years ago Very-well adapted to prevailing glacial climate

Anatomically modern humans – Homo sapiens From around 198,000 years ago (the Omo skulls)

Some of the earliest known modern Homo sapiens; Herto, Ethiopia, 170,000 – 160,000 years ago

From Stringer, 2000

Chronology of Pleistocene sites (from Stringer, 2000)

xy.waikato.ac.nz:2048/nature /journal/v431/n7012/fig_tab/n ature02999_F1.html Homo floresiensis

6/ Nov2005.htm

“Flores man” tools Archaeology and age of a new hominin from Flores in eastern Indonesia M. J. Morwood et al. (2004) Nature 431, fig_tab/nature02956_ft.html

From Brown et al. 2004

H.sapiens H.erectus Pan microcephalic Comparisons of virtual endocasts H. floresiensis in centre (from Falk et al. 2005)

Species A TIME Convergent Evolution Species X

Species A TIME Species B Convergent Evolution Species X Species Z Species C Species Y Unrelated species look similar if they live in similar environments/ niche

Simpson 1980:70 Example of convergence: Sabre-tooth tigers Marsupial Placental

Dwarf elephant & hippo of Malta next to a modern Indian elephant Lecture16/MedMap.html

Dwarfism in island populations May evolve in response to restricted resource availability. Can happen very rapidly in mammals e.g. Malta’s extinct dwarf elephants evolved from a 4-metre ancestor in less than 5,000 years. Extinct dwarf elephants (Stegodon) were found in the same deposits as the Flores hominins.

Mirazon & Foley (2004): Homo floresiensis provides evidence that: hominins subject to same evolutionary rules as other mammals exposed to local isolation & small population sizes. supports the view that our evolutionary tree is a bushy one. Is consistent with idea that rapid & extreme climatic shifts of last 1 million years  dispersal, isolation, and localised evolutionary change.

Figure 1 Homo floresiensis in the context of the evolution and dispersal of the genus Homo. v431/n7012/fig_tab/ a_F1.html

Dr. Alison Campbell Department of Biological Sciences ACSNZ Biology Lecture 2006 King’s College