Human Genetics: Concepts and Applications (Lewis), 9th Edition

Chapter 16: Human Ancestry

Chapter Outline

CHAPTER OVERVIEW

1. Tracing the origin of our species requires techniques derived from many disciplines

1. Aegyptopithecus and Propliopithecus were monkeylike species that lived about 30 to 40 million years ago. Both are possible ancestors to gibbons, apes, and humans.
2. The ancestors of apes and humans were hominoids. The first Hominoids lived in Africa 22 to 32 million years ago.
3. Dryopithecus and species similar to it may have ventured onto grasslands due to selective pressures.
4. Three species, Ardipithecus kadabba, Sahelanthropus tchadensis, and Orrorin tugenensis, are possibly the earliest hominins.
5. Hominins were ancestral to humans only.

1. Hominins (human ancestors) appeared between 2 and 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.

1. By 2.3 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. The Neanderthals were contemporaries of Homo erectus. By about 24,000 years ago the Neanderthals no longer appear in the fossil record.

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 5,200 years ago is genetically like us.

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.

1. Small differences at the genome level can translate to large differences in phenotype.
2. This may result from changes in developmental control genes where a mutation in a single gene can exert a broad effect on phenotype.
3. Humans and chimps are genetically similar, but the degree of similarity depends on the comparison method.
4. Protein comparisons support a 98.7 percent sequence identity.
5. The human genome has undergone numerous duplication events since diverging from a vertebrate ancestor 500 million years ago.

1. Chromosome banding patterns are highly conserved in higher primates and reflect evolutionary relatedness.
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.

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.

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.

1. Markers such as SNPs, STRs and CNVs are being used to reveal how our species came to be dispersed across the world.
2. Mitochondrial DNA clocks trace maternal lineages, and Y chromosome sequences trace paternal lineages.
3. The Human Genome Diversity Panel is used to trace ancestry in many populations.

1. Molecular clocks have been used to examine the relationship of Neanderthals to modern humans.
2. Initial investigations using mtDNA sequence data suggested that Neanderthals were not direct ancestors of modern humans.
3. DNA analysis suggests that Neanderthals and modern humans shared a common ancestor before leaving Africa.
4. Neanderthal genome sequence data will continue to define differences and similarities with modern humans.

1. Mitochondrial DNA data support an "out of Africa" origin of Homo sapiens about 200,000 years ago.
2. Mitochondrial DNA and Y chromosome sequences have been used to trace ancestry in many populations including Native Americans.