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| 15.1 Human Origins 1. Propliopithecus and Aegyptopithecus were monkeylike species that lived about 30 to 40 million years ago. Both are possible ancestors to gibbons, apes, and humans. 2. Hominoids were ancestral to apes and humans. 3. Dryopithecus lived 22 to 32 million years ago and may have walked onto grasslands. 4. Hominids were ancestral to humans only. The Australopithecines-And Others 1. Hominids (human ancestors) appeared about 4 million years ago. 2. Four million years ago bipedalism opened up new habitats for australopithecines who walked upright and used tools. 3. There were several types of australopithecines, and one, A. garhi, may have been a direct ancestor of Homo. 4. A newly described species, Keynanthropus platyops, may have been yet another australopithecine or a contemporary. Homo 1. By 2 million years ago, Australopithecus coexisted with the more humanlike Homo habilis. 2. Later H. habilis coexisted with H. erectus, who used tools in more complex societies. 3. H. sapiens either coexisted with or arose from H. erectus 300,000-500,000 years ago. 4. The Neanderthals were contemporaries of Homo erectus and were displaced by the Cro-Magnons. By about 28,000 years ago the Neanderthals no longer existed while the Cro-Magnons gave rise to modern humans. Modern Humans 1. Evidence from the discovery of cave art demonstrates that by 14,000 years ago our ancestors had the ability to use symbols and had developed fine hand coordination. 2. A preserved man from 5,300 years ago is genetically like us. 15.2 Molecular Evolution 1. Evolutionary distances between living and extinct organisms can be estimated by studies that examine similarities and differences among chromosomes and sequences of proteins and nucleic acids. 2. The more alike two organisms are on a molecular level, the more likely it is that they share a common descent. Comparing Genomes 1. Whole genome comparisons indicate that humans differ from chimps by only 0.5 percent of their protein-encoding genes. 2. Small differences at the genome level can translate to large differences in phenotype. This may result from changes in developmental control genes where a mutation in a single gene can exert great effects on phenotype. 3. The similarity of all vertebrate genomes is seen in the comparison of the human and pufferfish genomes. 4. Only 40% of the human odorant receptor genes are functional. During the later stages of human evolution, a sense of smell may not have been the survival factor that it was in our ancestors. Comparing Chromosomes 1. Chromosome banding patterns is highly conserved in higher primates. 2. All mammals have identically banded X chromosomes. 3. Synteny is the correspondence of gene order in chromosomes in different species. 4. Identifying regions of synteny can reveal information about species relatedness and the evolutionary history of chromosomes. Comparing Protein Sequences 1. Many proteins are very similar in amino acid sequence in different species. 2. Homeobox proteins are transcriptional factors that control developmental processes in many organisms. 3. Homeobox genes are highly conserved throughout evolution. 4. Mutations in homeobox genes can cause disease in humans or bizarre morphological anomalies in flies and mice. 5. Evidence for functional relationships between conserved genes comes from experiments where genes encoding proteins of one species are transplanted into a distantly related species. Comparing DNA Sequences 1. The degree of evolutionary relatedness between two species can be estimated using DNA hybridization and observing how quickly the DNA forms hybrid double helices. 2. Comparison of DNA sequences between organisms reveals evolutionary relationships and is an important step in determining the function of newly isolated genes. 3. DNA obtained from preserved extinct organisms can be amplified and compared to DNA sequences in modern species. 15.3 Molecular Clocks 1. Molecular clocks apply mutation rates to time scales in order to estimate when two individuals or types of organisms most recently shared ancestors. 2. Parsimony analysis selects likely evolutionary trees from DNA data. Neanderthals Revisited 1. Molecular clocks have been used to examine the relationship of Neanderthals to modern humans. 2. Analysis of available DNA sequence data suggests that humans and Neanderthals did not ever interbreed. 3. Mitochondrial DNA analysis suggests that Neanderthals and modern humans last shared a common ancestor 550,000 to 700,000 years ago. Choosing Clues 1. Genes change (mutate) at different rates. Sometimes different conclusions arise from comparing different sequences. 2. Mitochondrial DNA clocks trace maternal lineages, and Y chromosome sequences trace paternal lineages. 3. Analyses of mitochondrial DNA and Y chromosome information has been used to examine the origin of modern humans in Africa or in many regions and the migration pattern of native Americans from Asia. 4. Mitochondrial DNA and Y chromosomal DNA support a "out of Africa" origin of Homo sapiens about 200,000 years ago. 5. An "out of Mongolia" model for the origin of Native Americans is supported by mitochondrial DNA and Y chromosomal DNA. Contributions from other Siberian populations are evident. 15.4 Eugenics 1. Eugenics is the control of individual reproduction for societal goals. 2. In the early twentieth century several different eugenic policies were promoted and implemented. 3. Positive eugenic policies aimed to maximize the genetic contribution of those deemed acceptable or superior (positive eugenics). 4. Negative eugenic polices were designed to minimize the contribution of those considered inferior. 5. Some aspects of genetic technology also affect reproductive choices and has been compared to eugenics. 6. The goal of genetic screening is to alleviate human suffering rather than to change society. 7. Laws have been proposed and passed in many nations around the world to prevent genetic discrimination. |