Ancient seeds give clues on climate change

Thousand-year-old seeds, and traces hidden in the soil for more than 5,000 years, have a lot to tell us. They provide clues to how people and the crops they grew for food were affected by climate change. Geologist Joyanto Routh and biologist Jenny Hagenblad claim that this knowledge may help us adapt to changes in our lifetime and in the future.

In a world where we often look to the future, it is easy to forget that the answers to some of our questions may be hidden in our history.

“The past holds the key to the present. We talk a lot about the future – what will the world look like in 5, 10 or 20 years? I remind my students that humans are a highly resilient animal – we adapt to change. Throughout history, those who have been able to adapt to change have been the ones who have flourished,” says Joyanto Routh, professor at Tema M – Environmental Change at Linköping University.

He is fascinated by extreme environments that are very dry today, but that have had a different climate in the past. How were the people who lived there affected by climate change and what happened to their city states?

“4,200 years ago, a worldwide phenomenon occurred that we now call the 4.2-kiloyear event. Drastic changes in monsoon rain patterns had a strong impact on the burgeoning settlements. This happened in Mesopotamia, China, the Indus Valley in India, and in what is now Iran. A nearly 3,000-kilometre-long area in Asia was affected.”

These well-developed Bronze Age settlements had flourishing farms that fed the cities.

“The large settlements either shrunk or were abandoned. But why? Was it because of the climate, or was it due to invasions, weak lines of succession or diseases?”

Joyanto Routh is a geologist. He teamed up with archaeologists to investigate two excavation sites in southeastern Iran. They gathered long drill cores from peat and dried-out lakes. Soil strata contain detailed evidence of how the environment and human activity have changed over millennia.

Joyanto wanted to investigate whether climate played a role in the decline of settlements and agriculture. Traces of pollen and various elements in the soil provided clues about how the climate changed between wet and dry periods.

“What probably happened is that people adapted to the changing climate. During prolonged dry periods when agriculture became untenable, they abandoned their settlements and switched to a more nomadic lifestyle. As conditions became more favourable, with more rain for instance, people returned and began to grow crops again,” says Joyanto Routh.

Climate changes thus contributed to cultural adaptations. Joyanto Routh believes that similar shifts occur in our time when people are forced to deal with the consequences of extreme weather phenomena, sea rise and slow changes that make some places uninhabitable.

“We can learn important things by investigating what happened in the past. How did people survive when conditions changed dramatically? How did they adapt? Can we use the lessons learned in the future? If we don’t understand how people adapted to climate variations in the past, it can be difficult to navigate everything that the future will bring.”

While Joyanto Routh searches for history hidden in ancient soil strata, Jenny Hagenblad finds information in plant DNA. She is particularly interested in the crops cultivated by man for a long time. In the plants that live today, she finds signals about what has happened before.

 “I’m fascinated by the fact that DNA contains information on the history of the population. The cultivated plants are so closely connected to us. We depend on them, and they have been shaped by us. And if we understand their history, we can benefit from that knowledge going forward,” says Jenny Hagenblad, senior associate professor at the Department of Physics, Chemistry and Biology.

Together with her colleagues, she has examined barley brought to the Canary Islands by people who came there from North Africa in the 3rd century. The settlers quickly colonised all seven islands.

“After a while, the people stopped being seafarers. The islands became isolated, even though they were within sight of each other. When European seafarers discovered them in the 14th century, different dialects, even different languages, were spoken on the islands.”

This isolation made not only the language, but also agriculture, develop in different directions. The first settlers had brought barley, emmer wheat, peas, beans and lentils to the islands.

“Since each island was isolated, crop failure or extreme weather could completely devastate, for example, bean cultivation on an island. It was impossible to get new seeds. On La Palma, over time, the people lost agriculture completely and instead lived on fishing and wild plants.”

On other islands, the population continued to grow ancestral crops for more than a thousand years. On Gran Canaria, surplus crops were stored in storage silos dug out of the rock in very inaccessible places.

Today’s scientists must use climbing equipment to get there. But it is worth the effort, because analysing the DNA of the old seeds can provide important clues. Jenny Hagenblad has examined 1,500-year-old barley and the analyses show that most of the barley grown today in the Canary Islands is of the same type as what the indigenous people cultivated.

“We think this is due to the climate. Even though the Spaniards, who replaced the indigenous people, brought their own varieties, these were probably outdone by local varieties that had adapted to the location and were much easier to grow there.”

These discoveries have had unexpected effects in the form of renewed interest in “genuine Canarian” barley and the dishes that the ancestors cooked with it.

By comparing barley of different ages, the researchers can also see how the species has changed over time in the location.

“We see that during certain periods of time certain genes appear to have benefited and this has been linked to the climate. One gene has to do with root growth, which is probably good for the plant if the climate has become drier. The genetic changes that have occurred between different eras are consistent with how the climate changed in that location at that time.”

According to Jenny Hagenblad, the climate-adapted old varieties may prove to be important for us being able to grow food also in the future.

“We can find genes that can be useful to cross into today’s crops if we want them to better withstand rain or drought.”