The so-called “out of Africa” theory has been debated alongside a multi-regional concept for years. The difference between the two is whether humans (Homo sapiens) evolved from one population or from multiple populations. The latest DNA evidence supports the evolution of humans from a single ancestor, meaning our evolution was a singular event. This means that Homo sapiens evolved from Homo erectus approximately 100,000 years ago in a single population rather than happening independently in several populations. This is a key point in time, because Homo sapiens was better equipped to spread and inhabit other lands, leaving Homo erectus to remain as only fossils.
In 2001, researchers looked at mtDNA to pinpoint human origins in Africa. Because we pass along a portion of our DNA to our offspring, researchers were able to reconstruct the timeline for the advancement of the gene pool by comparing the proportion of mutations at certain locations in the genetic code, called DNA markers. Mitochondrial DNA (mtDNA) is a subset of DNA within our cells, passed on from the mother to her children. Studies have also been done on the genetic variation in facial structure among early human populations. Other studies have studied markers on the Y chromosome to trace populations in Asia. These findings have elucidated more of the evolutionary mechanism behind human population expansion and relocation.
Placing human origins in Africa allows for a visualization of the spread of nomadic tribes across the continents. Over tens of thousands of years, humans transitioned from nomadic tribes to farmers. They built cities and established communities causing a need to adapt to different climates. New populations settled in colder regions such as Scandinavia and Europe, later to colonize America. Other tribes walked across Asia to the land bridge into the Americas even earlier than the Europeans’ arrival. Evolution within the human population then included the adaptation of skin color to compensate for differences in UV exposure in the north, but retention of pigmentation for those groups remaining along the equator.
Evolution occurs as an adaptation. Mutations in the DNA of a single individual can be passed along to offspring and spread within a population in a few generations. When the mutation determines survivability (ie. reproductive fitness due to survival into the reproductive years), it can alter what is dominant and what is recessive within the population. Some may argue that the Africa theory is wrong because white is a dominant skin color. Actually, pigmentation is a complex hereditary characteristic. It is dependent on the density of pigment cells in the skin as well as their activity. There is no simple on or off, there is a gradient of activity that can adjust throughout a person’s life. Within a single person there is also often not a consistent density throughout their skin. When observing this trait in a population the dynamics become even more complex. It must have truly offered an advantage and took thousands of years to develop in isolated populations to create the homogeneous (identical) populations we know today as races. But we all evolved from that first Homo erectus population and are Homo sapiens.
