Potts' Variability Hypothesis Has Biblical Support

Alice C. Linsley



Paleoanthropologist Rick Potts is the director of the Smithsonian’s Human Origins Program and curator of anthropology at the National Museum of Natural History. His research pieces together a record of Earth’s environmental change and human adaptation to environmental instability.

In this NOVA interview Dr. Pott's explains his "climate variability hypothesis" which he sees as a significant factor in human adaptability, settlement and migration. His idea has Biblical support.

Dr. Rick Potts

Dr. Potts said:

Climate change had always been on people's minds when it came to human evolution. The idea that was around for a long time is that the establishment of a savanna environment, the grassy environment with a few trees, was critical to human evolution early on, and that and the Ice Age later on presented the challenging environment in which humans evolved.

But when I began the work here at Olorgesailie, we kept seeing layer after layer of environmental change, from soils to volcanic ashes to a lake to a drought when the lake completely evaporated. We saw this through 700,000 years, and I began to think, well, maybe it's not the particular environment of a savanna that was important, but the tendency of the environment to change, to vary in very dramatic ways. And we saw that the large grazing animals of the savanna—elephants, baboons, pigs, zebras, all of whom ate grass—disappeared in the time period when worldwide climate began to vary the most.

So it dawned on me: Rick, you're an anthropologist. Maybe this has something to do with human evolution, and it's not the survival of the fittest in any one environment but the survival of the more versatile, the more general and flexible creatures that would really persist over time. This gave me a new insight into human evolution. The origin of stone tools, the expansion of the brain, and the complexity of social life that we see with the emergence of our own species may actually be a response not to just the dry savanna or the cold Ice Age but to the wide and dramatic variability of climate over time.

In some cases the landscape change occurred within a few thousand years. But this is all within a larger cycle of changing—Earth's orbit around the sun, and changes from wet to dry in tropical Africa, and, later in time, changes that were on [a scale of] 100,000 years between ice ages and interglacial warmth.

Olorgesailie inspired our idea that climate variability was an important driving force in human evolution. But we had to look outside of Olorgesailie to many other early human sites to really test the idea. What we have found is that the most prolonged periods of climate variability early on corresponded with the origin of stone tools and of eating meat, and the origin of our own genus, Homo. Then, later on, another prolonged period of climate variability, very dramatic, corresponded with the origin of modern human behavior and our own species.

(Read more here.)

The key points of Pott's hypothesis are evident.  Life on Earth is sustained by water. Climate has an impact of the availability of water. Factors that influence water accumulation in lakes and rivers are Earth's climate cycles and plate tectonics. When water sources disappear, humans and aminals must seek other sources. Where abundant water sources exist, there is greater evidence of human habitation.




Life Depends on Water

A close reading of Genesis reveals that climate is certainly a factor in archaic human settlement and migration. Humans settled near major bodies of water. This is where they hunted large game and buthered them with stone hand tools.  During rainy periods, lakes swelled and during dry periods, lakes disappeared.  Climate cycles caused old dry basins to fill with water. This swelling and shrinking of water systems is evident from satellite photos taken of Earth's great rivers and lakes.

Neolithic peoples in the Sahara enjoyed abundant water.  The Nile connected to the Chadic and Niger water systems through a series of shallow lakes in the Sahara. This explains the common plant and animal species is found in all three river valleys. The now dry Botswanan lake was once a sea. Some of Africa's earliest human populations lived on the edges of this great lake, as evidenced by the thousands of stone tools found there. These include maceheads that date between 80,000 and 100,000 years.

Between 12,000 and 8,000 years ago all of the region between Lake Chad and the Nile was wet. The climate had changed, ushering in years of persistent, heavy rains. A briefer period of rain lasted between 3000 and 1900 B.C. This is the the time of Noah's flood. Noah was a Proto-Saharan ruler in region of Lake Chad. People living in this area, called "Bor-No" (Land of Noah), claim that this is Noah's homeland.

Lake Chad has been shrinking for centuries, but today rains are returning to the Sahara. West Africa is receiving abundant convective rainfall. At the close of "Earth's Great Year" in the summer of 1998, air and water temperatures peaked and this has affected rainfall in some of Earth's most arid regions.

Tropical temperatures (latitude 20N - 20S)

In 2010, Pakistan saw catastrophic flooding from the Indus River. These NASA photos show the striking contrast within a single year.

NASA image captured in 2009

NASA image captured in 2010

Geologic Factors

Tectonics also played a role. Rifting and continental extension creates water systems and inland seaways such as the Humer Seaway in North America.

About 150,000 years ago there was a major uplift of the Angolan ridge in equatorial Africa. This meant a permanent supply of water flowing to the Upper Nile and prompted migration to that area. Lakes formed in the basins, large enough to support fish, crocodile and hippopotamus. Early hunters camped along the lakes, as evidenced by heaps of domestic refuse at many sites along ancient lakes in Niger, Chad and Kenya.

Lake Chad filled and merged with the Mega-Chad Sea, creating a body of water comparable in size of modern Sudan. The overflow spilled southwest into the Benue Trough and flowed to the Atlantic. The Nile was transformed from a slow stream into a roaring river with mile-deep gorges. This was the beginning of the wet period that would turn the Sahara into vast grasslands able to support elephants, antelopes, gazelles, ostriches, giraffes, and hyenas.




River Civilizations Emerged

This extended wet period led to the establishment of a Nilotic civilization which appears to have climaxed in dynastic Egypt and in the Kushite expansion into Mesopotamia (Gen. 10:8-12). The Kushite expansion lead to the river-based Sumerian and Akkadian civilizations. These civilizations were dependent upon river commerce and the rulers controlled and taxed that commerce.

To understand the Kushite expansion we must consider a factor beyond climate and river commerce, namely, the custom of sent-away royal sons, a feature of human adaptation that Potts has not considered. The marriage and ascendancy pattern of the Proto-Saharan and Nilotic rulers drove expansion and migration out of Africa through the custom of sending away firstborn sons who were expected to establish territories for themselves.




Sent-Away Sons

Genesis 2:24 speaks of how a man is to move away after marriage. This refers to sent-away sons of the ruling lines among Abraham's ancestors. “For this reason a man will leave his father and mother, and shall cleave unto his wife and they shall become one flesh.” The married son was expected to leave his parents and to establish a new household.  Most Westerners tend not to respect grown men who stay home, whether married or not. Stay-at-home sons often compete with their fathers or become "momma's boys." Jacob's stay-at-home son was Reuben and Reuben slept with his father's concubine, Bilhah (Gen. 35:22; 49:4). David's son Absalom did the same thing. Absalom ordered that a tent be set up on the palace roof where everyone could see it (ii Sam. 16:2). There Absalom went in and had sex with his father's concubines. This action represented an attempt to usurp the ruler's authority.

An anthropologist reading Genesis 2:24 finds evidence of the establishment of a new household geographically separate from the husband’s family. This is called “neolocal residence.”  However, analysis of the marriage and ascendancy pattern of Abraham’s Horite people indicates that the neolocal pattern does not apply to the firstborn sons of the patriarch’s wives. It applies only to sent-away sons who did not ascend to the thrones of their fathers or maternal grandfathers.  Most sons of concubines also were sent away and often served as vassals of the firstborn sons of wives.

Another feature of the Horite ruler-priest marriage and ascendency structure is alluded to in Genesis 2:24 which speaks of “cleaving to the wife.”  This indicates matrilocal residence, an arrangement where the newly married couple lives with or in close proximity to the bride’s family. This pertains to the firstborn son of the patriarch’s second (cousin or niece) wife. This son was the heir to his maternal grandfather, after whom he was named, and he lived with or near his mother’s people. So Abraham's firstborn son by his second wife belonged to the household of Joktan, Keturah's father, after whom he was named.

Patrilocal residence pertained only to firstborn sons of the half-sister wife. This seems strange given the insistence of Bible scholars that ancient Hebrew society was patriarchal. This is why Isaac remained in Abraham's territory and why Abraham gave gifts to his other sons and sent them away from Isaac (Gen. 25:6).

Genesis 2:24 pertains to sons who lived away from their biological fathers. This includes “sent-away sons” and the firstborn son of the patriarch’s second wife. Jacob's case is especially interesting. He was not Isaac's firstborn son and though he attempted to rob that birthright from Esau, Jacob established his residence with his mother's people. This suggests that Jacob and Esau may not have been twins. They may have been Isaac's firstborn sons by different wives. Esau was the firstborn of Isaac's first wife who would have been Isaac's half-sister. Jacob would have been the firstborn son of Isaac's second wife. As the second wife was either a cousin or niece, as was Rebecca to Isaac, Jacob would have been Rebecca's firstborn son. As such he would belong to the household of his maternal grandfather, Bethuel. However, this doesn't mean that Jacob was heir to Bethuel's throne in Padan-Aram. Bethuel's heir appears to have been Laban.

Sent-away sons is a prominent theme in Genesis. Some see the story of Adam's expulsion from the garden as the first example.  However, Adam's historicity cannot be proven.  among verifiably historical figures we see this pattern with Cain who was banished for killing his brother. we find it at the end of Genesis in the account of Joseph who was sold into Egyptian captivity by his brothers.

The pattern continues in Exodus where Moses is forced to leave Egypt after killing a fellow Egyptian.  He travels to his Midianite kin and marries a patrilineal cousin, Zipporah. This suggests that Isha, Amram's cousin wife, was a Midianite bride. The Midianites were descendants of Abraham by his cousin wife Keturah.

Other sent-away sons include Ishmael and Yishbak, both sons of Abraham. The name Yishbak means “sent away.”


Related reading: Genesis and Climate Change; Climate Cycles Indicate a Dynamic Earth; Climate and Noah's Flood; When the Sahara Was Wet; Water Systems Connected Nile and Central Africa;
Sub-Saharan DNA of Modern Jews; Abraham's Sons