“This is not a book on human origins. Rather it is about the journey we have taken as a species, from our birthplace in Africa to the far corners of the earth, and from the earliest evidence of fully modern humans to the present day—and beyond.”
It is likely we all have been asked, “Where do we come from?” by one of our sons and daughters or nieces and nephews. We all have also given an answer to the child and we all know where we come from in the hospital. But where do we really come from? We have genealogies that describe the ‘roots’ of our families but then they too stop at a point in history. Where did that first dude in our families come from? More importantly, where did humans come from?
Two most popular theories of Human evolution are “Out of Africa theory” and “Multiregional Origins theory.” The former contends that humans evolved in Africa then spread around the world. Due to adaptations to various climates the modern humans look different in various parts of the world. The latter argues that humans evolved form previously existing hominids in various parts of the world and thus, the morphological difference.
Although “Out of Africa theory” is accepted by most scientists today, “Multiregional Origins theory” was also popular in the past. Carl von Linneus, who innovated binomial system of nomenclature (Genus and species names), like Darwin, also recognized that all humans belong to the same species. However, he added sub-classifications based on morphological differences of humans; for example, an African was named Homo sapiens afer. This system of classification was adored by the American proslavery lobby to justify the brutality of the slaves in the United States. Although multiregional theory was discarded by scientists and church (because it conflicted with Adam and Eve), there were anthropologists and archeologists who believed in it and a few still do. Such beliefs also led to popularity of Eugenics, which attempted to “improve the gene pool of humanity through the selective breeding of ‘fit’ individuals.” Proponents of eugenics were involved in forced sterilization of ‘unfit’ individuals in the US and principles of eugenics also resulted in “systematic extermination of Jews, gypsies, homosexuals and other supposedly inferior groups by the Nazis in the 1940s.”
History teaches us that classification of humans based solely on morphology (appearance) can be misleading. Before 1900, anthropologists and archeologists were concentrating on morphological and linguistic differences but a huge leap in science was taken in 1901 by Karl Landsteiner, who discovered blood groups. Classification of humans using blood groups was “the first demonstration of biochemical diversity among living humans.” Diverse frequencies of blood groups among different peoples from all around the world including the Egyptian mummies verified a peek of human diversity. Using the blood groups data, it was discovered that “the majority of the genetic differences in humans were found within populations” and a small difference was found among populations. In 1930s, scientists took one step further by discovering that proteins can act as molecular time clocks. By observing hemoglobin in various animals they discovered that the closer the animals were, the more identical their hemoglobin was. Proteins are encoded by DNA (genes) and it would be best to study DNA itself to study variation. But it was not possible to study DNA in their times due to lack of such technology.
Science develops very fast and scientists did not have to wait for very long to start analyzing the DNA. In 1980s, Professor Allan Wilson of University of California, Berkeley was one of the pioneers to adopt molecular biology techniques to study DNA. There are two types of DNA in our cells, we have our chromosomes inside the nucleus and there is mitochondrial DNA (mtDNA) in mitochondrias outside of nucleus. Since one has to account for recombination in nuclear DNA, Wilson was very clever to use mitochondrial DNA to study variation in humans. Mitochondrial genome exists in only one copy and thus there is no recombination but it has more polymorphism (variations) per length of DNA. They sampled many individuals from around the world and reached the following conclusion-“All these mtDNA stems from one woman who is postulated to have lived about 200,000 years ago, probably in Africa.” This woman is known as Mitochondrial Eve. This does not mean that Mitochondrial Eve was the only female alive at that time. It means that there were many females but it was only her descendents that made it to present the descendents of other females died out. The “Out of Africa theory” was born.
It is not only our mtDNA that takes us to Africa in search of our ancestors. Other genes such as beta-globin, CD4, and Chromosome 21 all direct us to African ancestry. Mitochondrial DNA is used to identify out maternal lineage only because we inherit our mitochondrias only from our mother. Conversely, another chromosome in our nuclear genome, Y chromosome, tells us the story of our paternal lineage. It was the innovative peoples in the laboratory of Cvalli-Sforza at Stanford who figured out a way to analyze polymorphisms in Y chromosome and dated the Y chromosome Adam to be 59,000 years old, much younger than the mitochondrial Eve! Does that mean men evolved alter than women? No. It just means that all present day men are derived from the same man living 59,000 years ago and the men before him had descendants who did not make it to the present days. The astonishing fact is that humans were still in
Africa until 60,000 years ago!
There are so many peoples living in Asia and Indonesia is the fossil factory because every now and then we hear about some new fossils being discovered in Java. Then why Africa? Archeological expeditions have discovered lots of fossils in Africa not only of modern man but also of earlier hominids dating millions of years ago. In addition, some fossils are also the links between earlier hominids and modern humans. Also, modern Africans are genetically more diverse than people anywhere else. Combine these facts and we may conclude that our species evolved out of Africa. Also, it is important to understand that Africans are not less evolved than us. The modern Africans are as evolved as any other modern humans. In addition to mtDNA and Y chromosomes, there are other evidences that lead scientists to return to Africa in search of our ancestors. Linguists believe that one of the earliest languages spoken by humans consisted of clicks-clacks and the only people living today who speak the click-clack language are the San peoples of south-western Africa. Thus Linguistic, mitochondrial DNA and Y chromosomes suggest that San peoples “represent a direct link back to our earliest human ancestors.”
Why did humans migrate out of Africa in the first place? It is not true that humans were the first to migrate out of Africa, other hominids before modern humans had stepped in Asia and Europe. However, it was the more intelligent modern man that was able to persist and eventually be the sole owners of the world. The theory of ‘the Great Leap Forward’ proposes that tools, art (conceptual thought), and exploitation of food resources caused major changes in Human behaviour and language was the force behind it. Africa once used to harbor plenty of flora and fauna. There were lots of animals to hunt and the person who could speak and make tools to hunt was able to hunt efficiently and feed his family. He would also mate more women and have more children. When his children grew up, they were smarter than others and they would produce more children. This way in a few generations, the clan would be mostly the descendants of that one man who was able to speak and use tools. Although humans were getting smarter, the climate change in Africa due to the Ice Age 70,000 years ago made life harsh. When humans found it increasingly hard to survive, a few started to take off from their homeland to a nearby area in search of food and water. Gradually they went farther and farther until they conquered the farthest corners of the globe.
Now we understood that humans migrated out of Africa in search of food but how did they manage to reach various parts of the world? There are two proposed routes of migration out of Africa–the inland route and the coastal route. The inland route led humans to the Middle East 50,000 years ago and then to central Asia 35,000 years ago. Due to the Ice Age, the Sahara started expanding in Africa about 70,000 years ago but retracted around 50,000 years ago allowing a gateway to open along the Red Sea. Thus,
Sahara might have acted as “hominid ‘pump’” sustaining human populations in winter but turning into “uninhabitable desert, forcing human emigration” in summer. Once the humans reached the Middle East, they were trapped there because the Sahara reached its driest between 40,000-20,000 years ago. Also, the moisture rich habitat of the Middle East offered a healthy habitat with plenty of food and water resources to humans who had already developed language and used stone tools. From there, it was an easy path for them to wander into central Asia and Mongolia.
From the Middle East, humans gradually entered Asia. In Asia they reached the Pamir Knot (present day Tajikistan) after crossing Hindu Kush only to encounter the barrier that no human had encountered hitherto—the Himalayas and the Tien Shan mountains. The Himalayas was conquered only in the 20th Century by Edmond Hillary and Tenzing Norgay with the aid of modern tools. There was no way our ancestors could have conquered these giant mountains. As a result, they split. One group moved southward into the Indian Subcontinent and the other went northward into Central Asia. According to Y chromosomes studies, our ancestors reached India around 30,000 years ago and central Asia 35,000 years ago using the land route. As the temperature decreased due to the ice age in the northern globe, the humans who went northward form the Hindu Kush had to adapt to the increasing cold. However, the availability of animals for hunting ensured their survival. In China, the two populations that diverged in
Africa, the ones that took the Coastal route and the latter that took the inland route met later. Although humans reached India 30,000 years ago via the land route, the coastal immigrants had reached the Indian soil much earlier (50,000-60,000 years ago). The remnants of this migration are still found in Andaman Islands and in various relict tribes across Asia. Even the Australian Aborigines share the so called ‘Negroid’ features with the Africans. The inland route populated Northern India while the coastal route populated the southern India. The coastal route seems to be the most ancient population that migrated out of Africa and reached Australia through India and South Asia. And later (within last 10,000 years) they moved up north through eastern Chinese coastland and south-eastern Siberian eventually ending up in
Although coastal migrants reached Americas 10,000 years ago, they were not the first to get there. The first Americans were the Siberians who shared their ancestors with the Europeans. Before 1997 people believed that Europeans descended from Neanderthals, an early branch of hominids that diverged from our common ancestor about 250,000 years ago. However, analysis of mtDNA of Neanderthals demonstrated that “Neanderthal was not the direct ancestor of modern humans. Rather, Neanderthals represented a local population of archaic hominids who were later replaced by Homo sapiens—with no detectable admixture.” The ancestors to the modern Europeans probably reached Europe 30,000 years ago. Although it seems logical to assume that humans moved to the Middle East from Africa and then to Europe, it was not the case. The ancestors of the Europeans come form the small population that went to Pamir Knot (Tajikistan) after splitting in the Hindu Kush. This date is also supported by the fact that Neanderthals vaporized at about the same time from Europe and ‘Aurignacian stone tools’ started appearing. Finally, humans did manage to reach Europe through the Middle East but only about 10,000 years ago.
The ancestors of humans that led to populate Europe also gave rise to the ancestors of the Siberians who occupied the Asian Arctic about 20,000 years ago. It did take humans to adapt culturally to conquer the extreme of Siberia. However, Siberia was not where humans stopped. Archeological findings have suggested a relationship between Siberians and Native Americans. Nuclear and mtDNA analysis validated that humans entered North America through the Bering Strait about 10,000-15,000 years go. Once they reached the grasslands of North America, their population grew exponentially aided by abundance of food and water and much warmer climate. In no time (about 1,000 years) the humans had reached the tip of
South America. However, Siberians were not the only immigrants to reach Americas. Linguistic and Genetic results demonstrate that the Coastal migrants also reached North Americas after the Siberians. These newcomers came through Northern China to south-eastern Siberia and then to North America by boat.
Thus, in mere 40,000 years, humans had reached the farthest corners of the world. They had conquered deserts, oceans, mountains, and even the freezing arctic. Although this may not be the answer our children are expecting, but it is definitely something we ought to know. Hey, after all, we are connected one way or another.