5.4 Tracking Genomes: Our Human Story Unfolds
3 min read•june 24, 2024
The suggests modern humans originated in Africa and spread globally. Evidence from mitochondrial DNA and genetic diversity supports this theory, with African populations showing the highest genetic variation.
Genomic research, including studies of human parasites like lice, provides additional insights into human evolution. These findings align with fossil evidence, strengthening our understanding of human migration patterns and evolutionary history.
Out of Africa Model and Human Evolution
Out of Africa model evidence
Top images from around the web for Out of Africa model evidence
Above the Cloud: La scoperta di DNA denisovano in una grotta tibetana View original
Is this image relevant?
Macro-haplogroup L (mtDNA) - Wikipedia View original
Is this image relevant?
Above the Cloud: La scoperta di DNA denisovano in una grotta tibetana View original
Is this image relevant?
Macro-haplogroup L (mtDNA) - Wikipedia View original
Is this image relevant?
1 of 2
Top images from around the web for Out of Africa model evidence
Above the Cloud: La scoperta di DNA denisovano in una grotta tibetana View original
Is this image relevant?
Macro-haplogroup L (mtDNA) - Wikipedia View original
Is this image relevant?
Above the Cloud: La scoperta di DNA denisovano in una grotta tibetana View original
Is this image relevant?
Macro-haplogroup L (mtDNA) - Wikipedia View original
Is this image relevant?
1 of 2
- Proposes modern humans originated in Africa and migrated to other parts of the world
- Suggests all non-African populations descended from a single migration event out of Africa ~60,000-70,000 years ago (Upper Paleolithic)
- Mitochondrial DNA () inherited solely from the mother, allowing researchers to trace maternal lineages
- Accumulates mutations at a predictable rate, serving as a "molecular clock" to estimate timing of evolutionary events
- Studies of mtDNA from diverse human populations reveal African populations have the highest levels of genetic diversity
- Suggests African populations are the oldest, as they have had more time to accumulate genetic variations ( people, pygmies)
- Non-African populations show a subset of the genetic diversity found in African populations
- Indicates non-African populations descended from a smaller group of individuals that migrated out of Africa, carrying only a portion of the original African genetic diversity (, )
Genomic research in human evolution
- Human parasites, such as lice, have evolved alongside their human hosts and provide insights into human evolution
- Lice are host-specific, adapted to live on a particular species (head lice, body lice)
- Genetic analysis of human head lice and body lice suggests they diverged ~70,000-100,000 years ago
- Divergence thought to coincide with the origin of clothing, as body lice require clothing to survive
- Timing aligns with proposed migration of modern humans out of Africa based on fossil evidence ()
- Studying genetic diversity and distribution of human lice can provide information about human migration patterns and population movements
- Global distribution of lice lineages can reflect the spread of human populations across continents (Eurasia, Americas)
- Integrating genomic data from human parasites with fossil evidence strengthens understanding of human evolutionary history
- Concordance between these independent lines of evidence increases confidence in reconstructed timeline and patterns of human evolution (, Out of Africa model)
Human Genetic Diversity
Processes of human genetic diversity
- introduces new genetic variations into populations
- DNA replication errors, exposure to mutagens, and other factors cause changes in DNA sequences (, , )
- Mutations, if passed on to offspring, contribute to genetic diversity within and between populations
- refers to random changes in allele frequencies over generations
- In small populations, chance events can have a significant impact on which alleles are passed on, leading to changes in genetic diversity
- Bottleneck events, where a population is drastically reduced in size, can lead to a loss of genetic diversity ( disease in Jews)
- , or the exchange of genetic material between populations, can increase genetic diversity
- Migration and interbreeding between populations introduce new alleles and combinations of alleles (, )
- Admixture between previously isolated populations can result in increased genetic diversity in the resulting population (, African Americans)
- can shape genetic diversity by favoring certain alleles over others
- Alleles that confer advantages in specific environments may become more prevalent in populations living in those conditions (, )
- Balancing selection maintains multiple alleles in a population if they are advantageous in different contexts (, )
- studies how these evolutionary processes interact to shape genetic diversity within and between populations over time
- Interplay of these evolutionary processes, along with factors such as population size, migration patterns, and environmental pressures, contributes to patterns of human genetic diversity observed today
Key Terms to Review (25)
ABO Blood Groups: The ABO blood group system is a way of classifying a person's blood based on the presence or absence of certain antigens on the surface of red blood cells. This system is one of the most important blood group systems in human biology and has significant implications for blood transfusions and organ transplants.
Ashkenazi: Ashkenazi refers to the Jewish ethnic group originating from Central and Eastern Europe. They have a distinct cultural, linguistic, and genetic heritage that has been shaped by their historical experiences and geographic dispersal.
Bantu Expansion: The Bantu Expansion refers to the expansive migration of Bantu-speaking people across much of sub-Saharan Africa over several millennia. This large-scale movement and settlement of Bantu populations had a profound impact on the cultural, linguistic, and genetic landscapes of the regions they inhabited.
Deletions: Deletions refer to the loss or removal of genetic material from a DNA sequence. This can occur during the replication or repair processes of the genome, leading to the absence of one or more nucleotides in the genetic code.
Founder effect: The founder effect occurs when a small group of individuals breaks away from a larger population to establish a new population, leading to reduced genetic diversity and increased prevalence of certain genetic traits or disorders. This phenomenon highlights the significance of genetic drift in evolution, as the new population may not represent the genetic makeup of the original group, which can result in unique adaptations or increased susceptibility to specific diseases over generations.
Gene Flow: Gene flow is the transfer of genetic material from one population or species to another through interbreeding. It is a key evolutionary mechanism that introduces new genetic variation into a population, allowing it to adapt to changing environmental conditions over time.
Genetic Bottleneck: A genetic bottleneck refers to a sharp reduction in the size of a population, leading to a significant loss of genetic diversity within that population. This event can have profound implications on the future evolution and adaptability of the species.
Genetic drift: Genetic drift is the random change in the frequency of alleles (gene variants) in a population due to chance events. This process can lead to significant changes in a population's genetic makeup over time, especially in small populations, where random events can have a more pronounced effect. It contrasts with natural selection, which involves differential survival and reproduction based on advantageous traits.
HLA Genes: HLA (Human Leukocyte Antigen) genes are a set of genes that play a crucial role in the human immune system. These genes encode a group of proteins found on the surface of cells, which are responsible for recognizing and presenting foreign substances, such as viruses and bacteria, to the immune system for a proper response.
Homo sapiens: Homo sapiens, or modern humans, are the only extant members of the Homo genus. They are characterized by their advanced cognitive abilities, bipedal locomotion, and the ability to create and use a wide variety of tools to adapt to their environment. Homo sapiens are the focus of the topics 5.1 Defining the Genus Homo and 5.4 Tracking Genomes: Our Human Story Unfolds, as they represent the culmination of human evolution and the species that has come to dominate the planet.
Insertions: Insertions refer to the addition of genetic material, such as DNA sequences, into a genome or genetic sequence. This process is a fundamental mechanism in the evolution of genomes and can have significant implications for understanding our human story as it unfolds.
Khoisan: The Khoisan are an indigenous ethnic group in Southern Africa, known for their distinct physical features, language, and cultural traditions. They are considered one of the earliest inhabitants of the region and have played a significant role in the understanding of human origins and genetic diversity.
Lactase Persistence: Lactase persistence is the ability to continue producing the lactase enzyme into adulthood, allowing for the digestion of lactose, the primary sugar found in milk and dairy products. This genetic trait is particularly relevant in the context of the chapter '5.4 Tracking Genomes: Our Human Story Unfolds.'
Mbuti: The Mbuti are an indigenous hunter-gatherer people who inhabit the Ituri Rainforest in the Democratic Republic of the Congo. They are known for their unique cultural practices and close relationship with their forest environment.
Mestizos: Mestizos are individuals of mixed European (typically Spanish) and Indigenous American ancestry. The term is primarily used in the context of Latin American countries that were colonized by Spain, where the mixing of Spanish and native populations resulted in the emergence of this distinct ethnic group.
MtDNA: mtDNA, or mitochondrial DNA, is the genetic material found within the mitochondria of eukaryotic cells. Mitochondria are the powerhouses of cells, responsible for generating the majority of a cell's energy supply through the process of cellular respiration. The unique properties of mtDNA make it a valuable tool for tracking human evolutionary history and migration patterns, as described in the chapter '5.4 Tracking Genomes: Our Human Story Unfolds'.
Multiregional Hypothesis: The multiregional hypothesis proposes that modern humans evolved from archaic human species in different regions of the world, rather than originating from a single ancestral population. It suggests that human evolution occurred concurrently in multiple geographic locations, with gene flow and interbreeding between these regional populations leading to the emergence of anatomically modern humans.
Mutation: Mutation is a permanent, heritable change in the genetic material of an organism. It is a fundamental mechanism of evolution, as mutations introduce new variations into the gene pool, providing the raw material for natural selection to act upon.
Natural Selection: Natural selection is the process by which certain traits become either more or less common in a population over time. It is a key mechanism of evolution, where organisms with favorable traits are more likely to survive and reproduce, passing on those traits to future generations.
Out of Africa model: The Out of Africa model, also known as the 'Recent African Origin' model, is a theory that proposes modern humans (Homo sapiens) originated in Africa and then migrated out of the continent, replacing archaic human species in other parts of the world. This model is particularly relevant in the context of the chapter '5.4 Tracking Genomes: Our Human Story Unfolds'.
Point Mutations: Point mutations are single base pair changes in the DNA sequence of a gene. They are the most common type of genetic mutation and can have varying impacts on the resulting protein, from no effect to complete loss of function.
Population Genetics: Population genetics is the study of the genetic composition and changes within a population over time. It focuses on understanding the frequency and distribution of genetic variations, as well as the factors that influence the evolution of these variations within a given population.
Sickle Cell Trait: Sickle cell trait is a genetic condition in which an individual inherits one sickle cell gene and one normal gene. This results in the production of both normal and sickle-shaped red blood cells, providing some protection against malaria but also increasing the risk of certain health complications.
Silk Roads: The Silk Roads were a network of trade routes that connected the East and West for centuries, facilitating the exchange of goods, ideas, and cultural influences between civilizations across Eurasia. This vast system of overland and maritime trade routes played a crucial role in shaping the history, economies, and societies of the regions it traversed.
Tay-Sachs: Tay-Sachs is a rare and fatal genetic disorder that primarily affects the nervous system. It is caused by a mutation in the HEXA gene, which leads to the buildup of a fatty substance called GM2 ganglioside in the nerve cells, ultimately causing progressive damage and destruction of these cells.