how prehistoric water pit stops may have driven human evolution

Our ancient ancestors seem to have survived some pretty harsh arid spells in East Africa’s Rift Valley over five million years. Quite how they kept going has long been a mystery, given the lack of water to drink. Now, new research shows that they may have been able to survive on a small networks of springs.

The study from our inter-disciplinary research team, published in Nature Communications, illustrates that groundwater springs may have been far more important as a driver of human evolution in Africa than previously thought.

Great rift valley.
Redgeographics, CC BY-SA

The study focuses on water in the Rift Valley. This area – a continuous geographic trench that runs from Ethiopia to Mozambique – is also known as the “cradle of humanity”.

Here, our ancestors evolved over a period of about five million years. Throughout this time, rainfall was affected by the African monsoon, which strengthened and weakened on a 23,000-year cycle. During intense periods of aridity, monsoon rains would have been light and drinking water in short supply. So how did our ancestors survive such extremes?

Previously, scientists had assumed that the evolution and dispersal of our ancestors in the region was solely dependent on climate shifts changing patterns of vegetation (food) and water (rivers and lakes). However, the details are blurry – especially when it comes to the role of groundwater (springs).

We decided to find out just how important springs were. Our starting point was to identify springs in the region to map how groundwater distribution varies with climate. We are not talking about small, babbling springs here, but large outflows of groundwater. These are buffered against climate change as their distribution is controlled by geology – the underlying rocks can store rainwater and transfer it slowly to the springs.

The lakes of the African Rift Valley.
SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE

We figured that our ancestors could have stayed close to such groundwater in dry times – playing a greater part in their survival than previously thought. When the climate got increasingly wet, groundwater levels would have risen and made springs more plentiful – feeding smaller rivers and leading to lakes becoming less saline. At this point, our ancestors would have roamed across the landscape free of concerns about water.

Life and death decisions

To test this idea, we embarked on a computer experiment. If the springs and water bodies are thought of as the rest stops, or service stations, then the linkages between can be modelled by computers. Our model was based on what decisions individuals would have taken to survive – and what collective behaviours could have emerged from thousands of such decisions.

Individuals were give a simple task: to find a new source of water within three days of travel. Three days is the time that a modern human and, by inference, our ancestors could go without drinking water. The harder and rougher the terrain, the shorter the distance one can travel in those vital three days.

We used the present landscape and existing water springs to map potential routes. The detailed location of springs may have changed over time but the principles hold. If our agent failed to find water within three days, he or she would die. In this way we could map out the migration pathways between different water sources as they varied through 23,000-year climate cycles. The map shows that there were indeed small networks of springs available even during the driest of intervals. These would have been vital for the survival or our ancestors.

The model also reveals movement patterns that are somewhat counter-intuitive. One would assume that the easiest route would be along the north to south axis of the rift valley. In this way, hominins could stay at the bottom of the valley rather than crossing the high rift walls. But the model suggests that in intermediate states between wet and dry, groups of people may have preferred to go from east to west across the rift valley. This is because springs on the rift floor and sides link to large rivers on the rift flanks. This is important as it helps explain how our ancestors spread away from the rift valley. Indeed, what we are beginning to see is a network of walking highways that develop as our ancestors moved across Africa.

Mapping human migration.

Human movement allows the flow of gossip, know-how and genes. Even in modern times, the water-cooler is often the fount of all knowledge and the start of many budding friendships. The same may have been true in ancient Africa and the patterns of mobility and their variability through a climate cycle will have had a profound impact on breeding and technology.

This suggests that population growth, genetics, implications for survival and dispersal of human life across Africa can all potentially be predicted and modelled using water as the key – helping us to uncover human history. The next step will be to compare our model of human movement with real archaeological evidence of how humans actually moved when the climate changed.

So next time you complain about not finding your favourite brand of bottled spring water in the shop, spare a thought for our ancestors who may died in their quest to find a rare, secluded spring in the arid African landscape.

The ConversationThis research was carried out in partnership with our colleagues Tom Gleeson, Sally Reynolds, Adrian Newton, Cormac McCormack and Gail Ashley.

Matthew Robert Bennett, Professor of Environmental and Geographical Sciences, Bournemouth University and Mark O Cuthbert, Research Fellow in Groundwater Science, Cardiff University

This article was originally published on The Conversation. Read the original article.

seacoast roads under new threat from rising sea level

Research out of the University of New Hampshire has found that some roads, as far as two miles from the shore, are facing a new hazard that currently cannot be seen by drivers – rising groundwater caused by increasing ocean water levels.

Researchers have identified sections of specific New Hampshire Seacoast roads that are the most vulnerable as groundwater levels continue to rise. They include the heavily traveled Route 286 in Seabrook and Gosling Road in Portsmouth. Without drastic improvements to these routes, at or below the pavement surface, motorists can expect segments of these roadways to deteriorate more quickly, require more maintenance and be closed for longer periods of time, according to a study recently published in Transportation Research Record.

“Previous road vulnerability studies have looked at road surface flooding, but groundwater has not been addressed,” said Jayne Knott, a civil engineering doctoral candidate in UNH’s College of Engineering and Physical Sciences and lead author of the study. “We found that the effects of surface water flooding on roads occur within a mile of the coast, and groundwater rise effects can occur more than twice that, sometimes all the way to Pease Tradeport.”

UNH notes that groundwater levels are higher than sea levels and that drives the groundwater discharge to the ocean. But as sea levels begin to rise, this forces groundwater to slowly move up to maintain the equilibrium, inching closer to the pavement base layers that need to stay dry to defend their strength.

“The worst enemy of pavement is water,” says Jo Daniel, professor of civil and environmental engineering, director of UNH’s Center for Infrastructure Resilience to Climate, and a co-author on the study. “If the soil and substrate under the pavement get wet, then the strength that we had counted on to carry the traffic isn’t there anymore. So the pavement develops ruts and cracks, allowing more water to get into the underlying layers which makes the situation worse and closing roads for long periods of time to dry out impacting both commuters and tourists.”

For the study, the research team examined the cross-section data for the most endangered sections of five Seacoast roads — Spaulding Turnpike, Gosling Road, Route 286, Route 101 and Middle Street. Highways are usually built more stout with thicker cross-sections of materials to withstand heavier traffic, while smaller town roads are sometimes little more than layers of pavement over shallow depths of crushed gravel. The thickness of the pavement base layers provides a buffer that protects the road as groundwater rises. The roads where groundwater is already close to the surface are the ones that will likely be affected first, although local geology, topography, soil type and drainage can also influence this.

Researchers then compared the N.H. Department of Transportation (NHDOT) road cross-section data with current and projected groundwater levels given various sea level rise scenarios ranging from one foot by 2030 to 6.6 feet by the year 2100. The results indicate that although Route 101 and the Spaulding Turnpike will probably not have many adverse issues by rising groundwater until late in this century, both Route 286 — an emergency evacuation route — and Gosling Road are likely to be some of the first roads affected.

— Read more in Jayne Knott et al., “Assessing the Effects of Rising Groundwater from Sea Level Rise on the Service Life of Pavements in Coastal Road Infrastructure,” Transportation Research Record 2639 (2017) (DOI: http://dx.doi.org/10.3141/2639-01)

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