Out of Africa: The Genetic Journey By William Lama, Ph.D.
Out of Africa: The Genetic Journey
By William Lama, Ph.D.
“Out of Africa” movie, Britannica Images
In the past few issues of Palos Verdes Pulse I have described the revolution in the life sciences brought about by the discovery of the DNA structure, the genetic code and the human genome. DNA sequencing is uncovering the genes with mutations that cause disease and disability. And the new field of Precision Medicine is making use of that data to target prevention and treatment strategies to individuals, rather than the traditional shotgun, one-size-fits-all approach. Gene therapy has become an engineering process driven by CRISPR technology. (See References)
Genetic information is also being used to predict human traits ranging from the weighty (the fat gene FTO) to the sublime. (Does your DNA make you LOL? - 23andMe Blog) I avoided a discussion of gender or racial traits related to genetic differences. Sometimes truth is an overrated value. When your spouse asks if she looks fat in her pre-covid outfit, the socially correct response is “Honey, you look GREAT.”
Here I will discuss another use of the new genetic data. It turns out that DNA can reveal the history of modern humans - Homo sapiens - and their journey from the African Garden of Eden. In The Descent of Man, published in 1871, Charles Darwin hypothesized that our ancestors originally came from Africa since, among all animals, the African apes were the most similar to humans. In the nineteenth century, that was a risky proposition. Yet even before Darwin’s time, Neanderthal man (Homo neanderthalensis) had been discovered (1864) and popularly thought to be the “missing link.” Now we know it to be a hominin - a species regarded as human, ancestral to Homo sapiens.
In the 1980s, DNA offered a new way to investigate the deep past. In 1987, researchers analyzed mitochondrial DNA from people around the world. The mitochondrion is the portion of the cell outside the nucleus that provides energy for the cell to do its work. Mitochondrial DNA (mt-DNA) is inherited from mother to child and undergoes no genetic reshuffling. It’s not fully understood what happens to the father’s mitochondrial DNA. Large structures called autophagosomes are known to engulf paternal mitochondria shortly after a sperm penetrates an egg. But is that the end of it? Scientists recently studied mitochondria in the sperm of a roundworm called C. elegans to find the answer. It turns out that paternal mitochondria in this roundworm have an internal self-destruct mechanism that gets activated when a sperm fuses with an egg. The paternal mitochondria in the roundworms actually started to break down before any autophagosomes reach them. “It’s like a suicide mechanism.” Why Do We Inherit Mitochondrial DNA Only From Our Mothers? - The New York Times (nytimes.com)
Thus, mt-DNA preserves a record of maternal ancestry. A family tree built from the genetic data had two main branches: one held only African lineages and the other contained lineages from all over the world. This pattern suggested the “mother” lineage came from Africa. Furthermore, based on the rate at which mt-DNA accumulates mutations, the researchers calculated that African Eve lived about 200,000 years ago.
Mitochondrial Eve Mitochondrial DNA and human evolution | Nature
The African origin of Homo sapiens is now an accepted theory. However, the era when modern humans ventured “out of Africa” has been the subject of fierce debate. New genetic evidence and new dating techniques suggest that Homo sapiens began their journey from Africa around 100,000 years ago. Remarkably that was the beginning of the last Ice Age and really cold, even in Northern Africa. Given the severe environmental conditions, scientists still aren’t sure how our human ancestors managed to pull off this remarkable migration. Subarctic climate for the earliest Homo sapiens in Europe (science.org)
For a paleoanthropologist, studying ancient DNA is like an astronomer getting a new telescope that sees deeper into space with a different wavelength of light. Data from ancient DNA has been used to estimate human routes of divergence. Fossils and ancient DNA paint a vibrant picture of human origins | Science News These data are summarized in the following map.
Out of Africa migration of Homo sapiens Map of Homo Sapiens Migration (Illustration) - World History Encyclopedia
Much of the genetic data came from the National Geographic Society’s Genographic Project. This study sought to map historical human migration patterns by collecting and analyzing human DNA samples. About a million individuals played an active role in the quest to map the genetic journey of us all by contributing their own DNA to the project. National Geographic Genographic Project Review | PCMag
But paleoanthropology is like solving a jigsaw puzzle without all the pieces; any new piece can change the picture. That happened in 2010 when researchers assembled the Neanderthal’s genome and compared it with modern human DNA. They came to a startling conclusion: one to four percent of non-African DNA comes from Neanderthals. “We were naïve to think that humans just marched out of Africa, killed some Neanderthals, and populated the world.” Once modern humans migrated from Africa some fraction mated with other hominins including Neanderthals. Neandertal genome yields evidence of interbreeding with humans | Science News
My friend Jim Jones, a member in good standing of the Bakery Boys (we meet at Mayer’s Bakery) and a fine specimen of the species H. sapiens, contributed his DNA to the study. Jim found that his ancestors arrived on the coast of France around 40,000 years ago. No trace of any Neanderthal DNA was detected in his sample. On the other hand, the Bakery Boys agree that my DNA must be at least 10% Neanderthal.
In this series of four essays, I have tried to provide a sense of the momentous changes that are occurring in the life sciences. For those who want a deeper picture, I recommend the references cited, particularly Human Diversity by Charles Murray, Blueprint by Robert Plomin and Sociobiology by Edward Wilson.
For a detailed look at genetic paleoanthropology there is no better source than Lone Survivors by Chris Stringer.
How did we become the only humans on earth?
Stringer addresses questions such as:
1. What behaviors identify modern humans and do those include language, art and music?
2. How did racial (regional) traits evolve and how significant are they?
3. Has human evolution stopped?
“Combining the thrill of a novel with a remarkable depth of perspective, the book offers a panorama of recent developments in paleoanthropology . . . refreshingly politically incorrect.” ―Jean-Jacques Hublin, Nature
References
Human Diversity in a Nutshell by William Lama, Ph.D. — Palos Verdes Pulse
Is Social Science an Oxymoron? by William Lama, Ph.D. — Palos Verdes Pulse
Polygenic Scores and Heredity by William Lama, Ph.D. — Palos Verdes Pulse
Revolutionary Gene Editing Technology by William Lama Ph.D. — Palos Verdes Pulse
Dr. William Lama has a PhD in physics from the University of Rochester. Taught physics in college and worked at Xerox as a principle scientist and engineering manager. Upon retiring, joined the PVIC docents; served on the board of the RPV Council of Home Owners Associations; served as a PV Library trustee for eight years; served on the PV school district Measure M oversight committee; was president of the Malaga Cove Homeowner's Association. Writes about science, technology and politics, mostly for his friends.
email: wlama@outlook.com
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