Homo Sapiens Genetics and Diversity

Mitochondrial Eve

All living humans can trace ancestry to a single African woman, Mitochondrial Eve, who lived ~200,000 years ago (200 kya).
This conclusion is drawn from Mitochondrial DNA (mtDNA) analysis.
Mitochondria exist in large numbers within each cell, containing their own DNA.
mtDNA is distinct from human DNA and is passed down through the maternal line.
Males are considered "dead ends" in mtDNA lineage tracing because they do not pass it on.
Regardless of gender, individuals inherit mtDNA from their biological mother.

The chart depicts the relationship of mtDNA lineages globally.
Vertical branches represent individuals from major populations.
Taller vertical distances indicate greater sequence divergence.
Sequence divergence arises from accumulated mutations.
African populations exhibit the deepest nodes, indicating longer habitation and greater sequence divergence.
Populations in Northeastern Africa share mtDNA with those outside Africa, likely due to migration.
By contrasting mtDNA mutations (represented as lightning bolts), the genetic distance between different populations becomes apparent.
For instance, comparing an Italian and an Australian sample reveals approximately 10 mutational differences, symbolizing their shared common female ancestor.
Comparisons between two African samples, like the Kikuyu and San Bushman, often show a larger number of mutations, such as 21. This difference highlights the longer evolutionary history within Africa. I/A_{CA}
The speaker showed another chart that had identical evidence as the first one, but flipped upside down and mirrored.
The speaker referenced a paper that shows how using mitochondrial DNA affects human migration.

While mtDNA traces the female lineage, the Y chromosome is used to trace the male lineage.
A significant portion of the Y chromosome doesn't pair with the X chromosome, allowing for tracing.
Analysis of the Y chromosome reveals a similar pattern to mtDNA, with the most divergence in African samples.
Y chromosome evidence supports the "Out of Africa" theory, aligning with mtDNA findings.
Y chromosome DNA dates back 70,000 years.

Mitochondrial DNA and Y chromosome DNA confirm that modern human populations are genetically close and diverged recently from a common ancestor.
A bottlenecking effect likely occurred as humans left Africa.
Homo sapiens replaced Neanderthals through demographic advantage and assimilation.
Modern humans show less gene diversity than local ape populations.

Neanderthals are genetically closer to humans than chimpanzee populations are to each other.
A chart compares mitochondrial diversity among ape species, including bonobos, chimpanzees, humans, gorillas, and orangutans.
Humans have a small genetic cluster, indicating limited diversity.
Early mtDNA data suggested no interbreeding between Neanderthals and humans.
Nuclear DNA evidence now confirms interbreeding occurred.

Genetic diversity within hominoid populations reveals that humans have less total genetic diversity as a species.
Local human populations maintain a high percentage (86%) of total genetic diversity.
Humans are highly inbred, sharing 99.9% of genetic material.

Humans migrated across the globe in waves, reaching Australia by 30,000 years ago and the Americas 10-13,000 years ago.
Subsequent mixing has overwhelmed local genetic oddities.
Global travel facilitates intermixing, unlike other species.

Race is a relevant issue, often categorized by skin color.
Skin pigmentation is a superficial genetic trait.
Historically, skin pigmentation was wrongly used as a proxy for biological information.
Skin pigmentation varies clinally with distance from the equator.
Melanin protects against UV radiation, acting as a natural sunblock.

MC1R, a gene on chromosome 16, relates to skin and eye pigmentation.
Skin pigmentation is controlled by multiple genes.
As one moves further away from the equator, there is less of a need for dark skin.
Natural selection is more prevalent closer to the equator.
There are few MC1R gene variants within African populations, and all preserve function.
Outside of Africa, there are more mutations, with many resulting in loss of function, leading to lighter skin.
Natural selection is more relevant closer to the equator for darker skin.
Genetic drift explains MC1R mutations outside Africa.

Race is not strongly correlated with genetics.
Races were developed to categorize people, but they correlate with biology.
Most genetic diversity is within populations (86%).
Population differences are clinal and influenced by environment.
Race is a social construct with no real biological linkage.
There are some environmental genetic differences in populations due to their environment such as red blood count in high altitude populations.
Race, based on a social setting, has negative impacts that have been made in the past.