9.2 – Establishing Phylogenetic Relationships

1. 9.2 – Establishing Phylogenetic Relationships Phylogeny • while Linnaeus classified organisms according to their morphological characteristics, Darwin wanted classification to reflect their evolutionary development (i.e. phylogeny) as well as their relationship with other species • aphylogenetic tree is a branching diagram showing the evolutionary relationships among species or other taxa

2. homologous structures are one of the best indicators of how closely organisms are related

3. Human Evolution – Skull Analysis • the many fused bones of human and chimp skulls match almost perfectly, indicating the pattern was inherited from a common ancestor • Skulls, even from the same species, can have a wide variety of shapes and sizes • The opisthion index can indicate whether a hominid species was bipedal or not • use the following Gizmo to compare the opisthion index in humans and chimps • http://www.explorelearning.com/index.cfm?method=cResource.dspView&ResourceID=576&ClassID=1629699

4. recall that the relatedness of species can be measured by comparing their genes and the proteins they code for • the strongest support for any phylogenetic hypothesis is the agreement of molecular data with other evidence like anatomical features

5. Cladistics • each branch of a phylogentic tree is called a clade, and each clade can nest within larger clades • each item in a clade may be a species, genus, family, or any other taxon • every clade consists of an ancestral species and all its descendants

6. a cladogram is a phylogenetic diagram that specifies the derived characteristics of a clade • each branch point represents where two species (or other taxa) diverged from a common ancestor • each clade is actually defined by several derived characters • the key rule in cladistics is that all the organisms of a particular clade must share homologous structures that do not occur outside the clade, known as derived characters

7. Phylogeny and HIV Evolution • recall the Libyan situation in 1998 described on P. 251 in which medical workers were accused of deliberately infecting children with HIV • it was determined that all HIV strains were very similar and it was likely that all the children were infected from the same source since HIV mutates rapidly at a known rate, it was possible to determine when the infecting strains diverged from a common ancestor it was shown that the lineages split before the medical workers arrived

8. Phylogeny of Primates and Humans • primates were one of the first placental mammals to evolve about 65MYA and are characterized by grasping hands with opposable thumbs, and forward-facing eyes • anthropoids are distinguished from pro-simians by having larger bodies and brains, fused skulls, and colour binocular vision • divergence of old- and new-world monkeys was followed by divergence of old-world monkeys and hominids which include humans and chimpanzees, our closest relative

9. hominids are humans and all of their ancestors that arose after their split with chimps, and are distinguished by bipedalism and large brain size • Ardipethicusramidus is one of the oldest known bipedal species which dates back 4.6MY • more similar to humans and ancestral apes than chimps, it shows that humans and chimps have evolved different features (like knuckle walking) afterthey diverged • while members of the genus Homoco-existed with australopithecines and with other Homo species (H. sapiens and H. neanderthalis as recently as 130 00 YA), only one species of the genus Homo survived

10. the oldest H. sapiens fossils were found in Ethiopia, indicating that humans evolved in Africa • humans migrated first to Asia, then in a second wave to Europe, SE Asia, and Australia • there is still debate as to when humans migrated to North America