Out of Africa Hypothesis & the Concept of Race

In recent decades, scientific breakthroughs have consistently lent increased support to the "Out of Africa" hypothesis, which asserts that modern humans originated in Africa, then migrated throughout the globe from there. Support for competing theories has virtually disappeared from scientific journals and peer-reviewed publications. Molecular biology (genetics), archaeology, geology and dendrochronology (tree-ring dating) all point to the likely conclusion that human populations originated in Africa about 100-200,000 years ago, migrating outside the African continent around 80,000 years ago.

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Geologic evidence is based on "Stratigraphy", which is the study of sedimentary layers. For example, modern human fossils are found deeper in sedimentary layers the closer you get to Africa. Dating methods add further understanding to this sequential evidence. Tree ring dating and radiocarbon dating combine to show dates of uncovered specimens throughout the world. The oldest anatomically-modern human fossils are found in Africa, with the oldest human fossils in other regions of the world dating to more recent dates. Generally, the farther from Africa, the more recent the dates of the oldest specimens in each respective region. Radiocarbon and tree-ring dating (dendrochronology) are the most reliable dating methods in dating specimens and artifacts.

Finally, genetic testing adds further perspective to the picture. All modern humans show one of three genetic mutations found in African populations, while African populations do not show later genetic mutations exhibited in non-African populations. Genetic analysis also provides added insight into chronology, by applying genetic mutation rates to samples to determine how long ago a specimen lived.

The multitude of tests performed by any of these technologies generally paint a similar picture of human history. If any of these methodologies were unreliable, then results would appear to be random across a broad spectrum. There are certainly anomalous test results on occasion that would appear to undermine any one or all of these techniques, but in any scientific study, the "statistical outliers" are thrown out, since the preponderance of evidence generally points to the truth.

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Illusions of Race

Studies regarding human origins and migrations reveal the fact that all people are truly part of the same human family, separated only by time and distance. Genetic studies in particular show that peoples of different "nations" or "races" are fundamentally equal. However, as they are separated by time apart, distance or other geographical barriers, groups of people will naturally develop along different trajectories. Even though humans are basically similar, their individualized geographic realities, along with the law of natural variance, dictates the development of varied languages, cultures, religions, and even values to an extent.

As a result, people from far-away or nearby "nations", or members of different "races", seem foreign to each other. In reality, "foreigners" are simply a mirror of ourselves if our mutual ancient ancestors had exchanged respective migratory paths.

Even more than cultural and language differences, humans have traditionally used skin color as perhaps the leading factor for categorizing or differentiating people, or even making generalizations or assumptions about people. The fact that skin pigmentation represents just one out of about 3.5 billion letters in the genetic code illustrates just how erroneous such generalizations are, and how the concept of race is simply a matter of perception.

The skin pigmentation gene governs the amount of melanin in the skin and hair. The more melanin, the darker the skin/hair, with lower amounts dictating lighter skin/hair. Higher melanin amounts drastically decreases the risk of skin cancer. As humans originated in sun-soaked Africa, liberal amounts of melanin was advantageous for this hairless species, causing anatomically-modern humans to evolve as a dark-skinned people.

Humans migrated out of Africa several thousand years later, as dark-skinned people comparable to modern sub-Saharan Africans. However, the farther north they migrated, the less melanin they needed in order to gain protection from the risk of skin cancer. In fact, in less sun-soaked climates, higher melanin (i.e. darker skin pigmentation) actually inhibits the critical production of vitamin D. In sun-rich environments such as Central Africa, there is enough UV-A being radiated to enable the sufficient production of vitamin D in people with elevated melanin levels. But this is not the case in less sunny environments to the north. Therefore, lower sun intensity means lower melanin levels are an evolutionary advantage.

The sun was somewhat less intense in Asia than the humans' point of origin in Central Africa. Therefore, over the course of several thousand years, somewhat lower levels of melanin were produced in the skin/hair of Asiatic humans, giving them a light brown pigmentation. The lightening effect was even more dramatic for humans in sun-poor Europe, whose melanin was pressured even further downward by natural selection (favoring individuals with sufficient vitamin D levels), to the point of producing very light colored skin, with lighter colors of hair also emerging in northern populations.

Genetic evidence indicates that both "white" skin pigmentation and even blue eyes first appeared in the Caucasus region (Southern Russia) around 10,000 BC. This is corroborated by archaeological evidence. Before 10,000 BC, cave drawings in Europe portrayed dark-skinned humans.

To summarize, skin color is merely a result of sunlight (UV-A) exposure of ancient ancestors over the course of thousands of years, which is then genetically passed down, with variations still present to this day. On average, those with darker skin pigmentation are inherently just as likely to be intellectually, physically and morally proficient as those with lighter skin pigmentation, based on a virtually identical genetic code.

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Overview of Scientific Disciplines Used to Understand Human Origins and Migrations

Geological Evidence: Stratigraphy

Stratigraphy is a branch of geology that studies the sedimentary layers. It is governed by the Law of superposition, which states that sedimentary layers are deposited in time sequence, with the oldest at the bottom, and the youngest at the top. Sedimentary layers are comprised of sedimentary rock, which is formed by minerals or organic materials that are compacted by sediment. The sediment (ice, water, dust, etc.) exerts considerable pressure until the mineral or organic matter forms into rock.

A percentage of fossilized human remains and material culture (artifacts) will be covered by sediment, and preserved in the sedimentary layer corresponding with its age. Fossils and artifacts do not get jumbled into other sedimentary layers. When a human dies, or a tool is left behind, it cannot become deposited into the sedimentary layer from the preceding time period, since it has become hardened rock, buried beneath several feet of loose and/or hardened soil. Once fossilized human remains or artifacts undergo the sedimentary process, they are permanently suspended in the layer associated with their time period, unable to change position between sedimentary layers (per Law of Superposition).

By itself, stratigraphy is useful in establishing sequential chronology. In other words, "order of appearance" can be established. For instance, if a certain species is found within a certain sedimentary layer, and another closely-related species is only found at a deeper layer, then you know that the species found in the deeper layer lived before the other species. In the case of the "Out of Africa" research, you would expect to find human fossils in  a deeper sedimentary layer than you would in Asia, while finding them in a deeper layer in West Asia than you would in Europe (the path humans took to arrive into Europe).

Even though exact or even approximate dating cannot be concluded by this method alone, there is substantial value in just the sequential chronology. However, sedimentary layers can be calibrated through other dating methods, such as radiocarbon and tree-ring dating. If fossils and artifacts within a particular sedimentary layer generally fall within a certain date range, then further findings within the same layer can be assumed to fall within this same date range.

Molecular Biological Evidence: Genetic Testing/Analysis

As stated above, genetic evidence shows that all human lineages trace back to common ancestry in Africa. Non-African peoples exhibit mutations found in African populations, as well as a common base genetic base. Generally speaking, the further you travel away from Africa, the less genetically-related the indigenous people are to Africans.

Population genetics are studied through both the mitochondrial DNA (maternal line) and Y-chromosome (paternal line). These are the only parts of the genome that are passed down from generation to generation virtually unaltered. In other words, they do not recombine. Each female receives her mitochondrial DNA directly from her mother, and each male receives his Y-chromosome unmodified directly from his father, so each type can be tracked from generation to generation. With this information, you can test indigenous populations to determine which other peoples they are most closely related to, which unveils a migration pattern that begins in northeast Africa. Or, if ancient human remains are uncovered still containing DNA, it can undergo genetic testing to establish a genetic marker to know which peoples inhabited which lands at certain time periods.

Y chromosome data shows that 80% of European men share a common ancestor going back 25,000 to 40,000 years ago, meaning that humans entered Europe no more recently than 25-40,000 years ago, based on this evidence.

Certainly, the more straight-forward part of this equation is the analysis of how closely groups of people are related to one another. Through the computation of genetic mutation rates, you can approximate how long ago a certain group of people inhabited a particular region. Mitochondrial and Y-chromosome DNA mutate only slightly from generation to generation, slight enough to easily link close relatives, but still enough to establish an estimated chronology. For example, if a skull possessing DNA were uncovered, genetic scientists can measure the difference in genetic code between the specimen and modern indigenous peoples, and then mathematically calculate the expected mutation rate (or the fastest and slowest feasible rates) to determine how long ago the person lived. Also, scientists can measure the difference in the genome sequence between two groups of people, to determine how long ago their most recent common ancestor lived. With this information, scientists can estimate the length of time it took for the two groups to migrate from the region where their most recent common ancestor resided to their current homeland.

Mutation rates can be established through the calibration with other dating techniques. For example, if uncovered human remains also include organic material, they can be subjected to radiocarbon testing. If the remains are also in close proximity to a wooden object that contains a cross-section of tree rings (cut or carved from a tree trunk), then dendrochronology can be used for further calibration. After the advent of writing, literary evidence can provide yet another chronological marker. Mutation differences can be compared against known chronological markers to determine a mutation rate.

With this being the case, mutation rates going back to 3000 BC are conclusively established. Most genetic scientists agree that the mutation rate is similar even before 3000 BC, but it could vary to an unknown degree, since there is no compelling evidence to suggest that the mutation rate has changed within homo sapiens by more than a negligible amount. Radiocarbon dating has been calibrated to a fairly high degree of confidence going back to about 30,000 years ago, and to some degree of confidence going back to 50,000 years ago. Tree-ring dating has been calibrated going back to about 10,000 years ago. With all of this fine tuning, dating via genetic mutation calculations has been fairly well established, within a fairly reasonable margin of error. 

Based on established mutation rates, the most recent common female ancestor (based on mitochondrial DNA analysis) of all humans lived in Africa around 200,000 years ago. This would also place the initial migrations out of Africa at about 75-100,000 years ago, and entry into Europe at about 50,000 years ago. Erring far to the faster end of the spectrum of potential mutation rates before 3000 BC, the most recent common female ancestor could be placed as recently as 100,000 years ago, with the migration out of Africa beginning about 50,000 years ago, and the initial entrance into Europe occurring about 25,000 years ago. On the other hand, erring on the far opposite end of the spectrum (slower mutation rates), our most recent common female ancestor could have lived as far back as 500,000 years ago.

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Archaeological Evidence: Radiocarbon Dating

Over the years, large numbers of ancient artifacts and human remains have been unearthed and catalogued. The advent of radiocarbon dating in the last half-century has introduced a fairly reliable way of assigning an approximate date to many archaeological finds. Radiocarbon dating is dependent upon the presence of some amount of organic material on the artifact or specimen. This can include any part of once-living matter, such as a tree, plant, animal or other organism.

All living things absorb a specific amount of "C14" (radioisotope carbon 14) while alive, based on the atmospheric content of C14. Once deceased, the amount of C14 absorbed will decay at a constant rate. C14 has a half-life of 5730 years (+/- 40 years), meaning half of the remaining C14 in an organism will decay every 5730 years. Virtually all of the C14 will decay over the course of about 60-70,000 years. In which case, radiocarbon dating could theoretically be used up to 70,000 years after the death of the organism.

The potentially extraneous factor is estimating the amount of C14 in the atmosphere over the past 70,000 years. Tree-ring dating has been calibrated to about 10,000 years ago, enabling the nearly-conclusive calibration of radiocarbon dating to 10,000 years ago. Analyzing plant and tree samples going back even further has helped scientists to gain an understanding of ancient carbon profile. Radiocarbon dating can also be calibrated with other types of radiometric methods. Most scientists agree that C14 levels have not changed significantly in the atmosphere over the past 50,000 years, but since there have been minor fluctuations, which are taken into account whenever a test is performed.

However, calibration is not necessarily precise, but it is generally within a reasonable margin of error according to most scientists. Other potential issues can arise. For example, specimens can be extracted unusual environments, where the organism consumed and/or absorbed large amounts of ancient carbon. An organism near a naturally-occurring carbonate aquifer is one such example, as these aquifers can percolate large amounts of old carbon into nearby environment. Or, instrumentation or user errors can taint results. When such flawed tests are performed, the error is generally quite obvious, since the results will usually be far off from the generally expected time frame. However, these are rare cases, and the bulk of the measurements will conform toward a statistical mean, showing that the preponderance of evidence will prove largely accurate. Those that are flawed will produce a random measurement, generally proving to be a statistical outlier. When extreme results are thrown out (common in any statistical/scientific study), the bulk of the data will generally produce results that are most likely to be representative of reality.

Dendrochronology: Tree-Ring Dating

Tree ring dating has been calibrated as far back as about 10,000 years. Samples are taken from a cross-section of a tree trunk. With certain species of trees in certain locations,  known ring-growth patterns have been established. Multiple samples can be taken out of a certain species within the same ecological system (ensuring same conditions) in order to statistically establish the most likely-to-be-correct growth pattern. Ancient chronology can be determined by taking a living tree, and comparing its rings to a dead tree that is hopefully much older. Each ring is very individualistic, like a finger print. Therefore, if one of the initial rings on the living tree (toward the middle) matches an outer ring on a dead tree, then it can be ascertained that the two overlapped, with the living tree sprouting to life toward the end of the dead tree's life. As a result, you can calibrate the chronology back even further into time, and so on and so forth as trunks from ancient trees are discovered in the area (even in the sedimentary layer). Through this process, dating has been calibrated going back as far back as about 10,000 years.

Once calibrated in a certain region, dendrochronology can be used to calibrate other dating methods applied to specimens and artifacts found in the area, such as radiocarbon dating and genetic mutation calculations. Stratigraphy can be used as a general guide to make sure that the sequential chronology produced by these other methods are correct. In other words, if one sample was found deeper in the sedimentary layers than another, the other dating methods should at the very least find it to be older.

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Comments (1)

The more we unlock mysteries previously hidden by the world, the more we find that our prejudices and differences are so superficial.

#1 - TP - 07/16/2009 - 16:21

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