Transcript HomoHobbit
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. 2 patterns of speciation: Anagenesis = change within a population; Cladogenesis = branching (divergence) to produce 2 new species. 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 http://sci.waikato.ac.nz/evolution http://www.geo.arizona.edu/ Antevs/ecol438/lect18.html Divergence Anagenesis (e.g. Pennisi 2006) http://www.staff.amu.edu.pl/~krzychu/ekologiaHS/html/humanFamilyTree.html 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) http://www.nature.com/nature/journal/v434/n7034/fig_tab/nature03397_F2.html 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? TIME Species A 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 http://www.staff.amu.edu.pl/~krzychu/ekologiaHS/html/humanFamilyTree.html 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”) http://www.staff.amu.edu.pl/~krzychu/ekologiaHS/html/humanFamilyTree.html Advances in cranial capacity What selection pressures would drive this? What selection pressures would act against it? http://www.geo.arizona.edu/Antevs/ecol438/lect18.html apes http://www.sas.upenn.edu/~ptschoen/papers/dissertation/Dissertationch2_files/image009.gif 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) Homo floresiensis http://www.nature.com.ezpro xy.waikato.ac.nz:2048/nature /journal/v431/n7012/fig_tab/n ature02999_F1.html http://www.yorku.ca/kdenning/+2140%2020056/2140-15Nov2005.htm “Flores man” tools Archaeology and age of a new hominin from Flores in eastern Indonesia M. J. Morwood et al. (2004) Nature 431, 1087-1091 http://www.nature.com/nature/journal/v431/n7012/ fig_tab/nature02956_ft.html From Brown et al. 2004 H.sapiens microcephalic H.erectus Pan Comparisons of virtual endocasts H. floresiensis in centre (from Falk et al. 2005) http://www.sciencemag.org/cgi/content/full/308/5719/242/FIG1 TIME Convergent Evolution Species A Species X TIME Convergent Evolution Species X Species A Unrelated species look similar if they live in similar environments/ niche Species B Species C Species Y Species Z Example of convergence: Sabre-tooth tigers Marsupial Placental Simpson 1980:70 Dwarf elephant & hippo of Malta next to a modern Indian elephant http://geography.berkeley.edu/ProgramCourses/CoursePagesFA2002/geog148/Lectures/ 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. http://www.nature.com.ezproxy.waikato.ac.nz:2048/nature/journal/ v431/n7012/fig_tab/4311043a_F1.html Dr. Alison Campbell Department of Biological Sciences ACSNZ Biology Lecture 2006 King’s College