A paper published in Proceedings of the National Academy of Sciences (PNAS) this week challenges this view. Dr. Kaboth-Bahr and an international group of multidisciplinary collaborators identified ancient El Niño-like weather patterns as the drivers of major climate changes in Africa. This allowed the group to re-evaluate the existing climatic framework of human evolution.

Walking with the rain

Dr. Kaboth-Bahr and her colleagues integrated 11 climate archives from all across Africa covering the past 620 thousand years to generate a comprehensive spatial picture of when and where wet or dry conditions prevailed over the continent. “We were surprised to find a distinct climatic east-west ‘seesaw’ very akin to the pattern produced by the weather phenomena of El Niño, that today profoundly influences precipitation distribution in Africa,” explains Dr. Kaboth-Bahr, who led the study.

The authors infer that the effects of the tropical Pacific Ocean on the so-called “Walker Circulation” — a belt of convection cells along the equator that impact the rainfall and aridity of the tropics — were the prime driver of this climate seesaw. The data clearly shows that the wet and dry regions shifted between the east and west of the African continent on timescales of approximately 100,000 years, with each of the climatic shifts being accompanied by major turnovers in flora and mammal fauna.

“This alternation between dry and wet periods appeared to have governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa,” explains Dr. Kaboth-Bahr. “The resultant environmental patchwork was likely to have been a critical component of human evolution and early demography as well.”

The scientists are keen to point that although climate change was certainly not the sole factor driving early human evolution, the new study nevertheless provides a novel perspective on the tight link between environmental fluctuations and the origin of our early ancestors.

“We see many species of pan-African mammals whose distributions match the patterns we identify, and whose evolutionary history seems to articulate with the wet-dry oscillations between eastern and western Africa,” adds Dr. Eleanor Scerri, one of the co-authors and an evolutionary archaeologist at the Max Planck Institute for the Science of Human History in Germany. “These animals preserve the signals of the environments that humans evolved in, and it seems likely that our human ancestors may have been similarly subdivided across Africa as they were subject to the same environmental pressures.”

Ecotones: the transitional regions between different ecological zones

The scientists’ work suggests that a seesaw-like pattern of rainfall alternating between eastern and western Africa probably had the effect of creating critically important ecotonal regions — the buffer zones between different ecological zones, such grassland and forest.

“Ecotones provided diverse, resource-rich and stable environmental settings thought to have been important to early modern humans,” adds Dr. Kaboth-Bahr. “They certainly seem to have been important to other faunal communities.”

To the scientists, this suggests that Africa’s interior regions may have been critically important for fostering long-term population continuity. “We see the archaeological signatures of early members of our species all across Africa,” says Dr. Scerri, “but innovations come and go and are often re-invented, suggesting that our deep population history saw a constant saw-tooth like pattern of local population growth and collapse. Ecotonal regions may have provided areas for longer term population continuity, ensuring that the larger human population kept going, even if local populations often went extinct.”

“Re-evaluating these patterns of stasis, change and extinction through a new climatic framework will yield new insights into the deep human past,” says Dr. Kaboth Bahr. “This does not mean that people were helpless in the face of climatic changes, but shifting habitat availability would certainly have impacted patterns of demography, and ultimately the genetic exchanges that underpin human evolution.”

The international MAGIC collaboration, made up of more than 400 global academics, conducted a genome-wide association meta-analysis led by the University of Exeter. Now published in Nature Genetics, their findings demonstrate that expanding research into different ancestries yields more and better results, as well as ultimately benefitting global patient care.

Up to now, nearly 87 per cent of genomic research of this type has been conducted in Europeans. This means that the way these findings are implemented may not optimally benefit people from non-European ancestries.

The team analysed data across a wide range of cohorts, encompassing more than 280,000 people without diabetes. Researchers looked at glycaemic traits, which are used to diagnose diabetes and monitor sugar and insulin levels in the blood.

The researchers incorporated 30 percent of the overall cohort with individuals of East Asian, Hispanic, African-American, South Asian and sub-Saharan African origin. By doing so, they discovered 24 more loci — or regions of the genome -linked to glycaemic traits than if they had conducted the research in Europeans alone.

Professor Inês Barroso, of the University of Exeter, who led the research, said: “Type 2 diabetes is an increasingly huge global health challenge- with most of the biggest increases occurring outside of Europe. While there are a lot of shared genetic factors between different countries and cultures, our research tells us that they do differ, in ways that we need to understand. It’s critical to ensuring we can deliver a precision diabetes medicine approach that optimises treatment and care for everyone.”

First author Dr Ji Chen, of the University of Exeter, said: “We discovered 24 additional regions of the genome by including cohorts which were more ethnically diverse than we would have done if we’d restricted our work to Europeans. Beyond the moral arguments for ensuring research is reflective of global populations, our work demonstrates that this approach generates better results.”

The team found that though some loci were not detected in all ancestries, they were still useful to capture information about the glycaemic trait in that ancestry. Co-author Cassandra Spracklen, Assistant Professor at the University of Massachusetts-Amherst, said: “Our findings matter because we’re moving towards using genetic scores to weigh up a person’s risk of diabetes. We know that scores developed exclusively in individuals of one ancestry don’t work well in people of a different ancestry. This is important as increasingly healthcare is moving towards a more precise approach. Failing to account for genetic variation according to ancestry will impact our ability to accurately diagnose diabetes.”

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Materials provided by University of Exeter. Note: Content may be edited for style and length.

The study, the largest of its kind, was led by the London School of Hygiene & Tropical Medicine (LSHTM) and the University of Bern within the Multi-Country Multi-City (MCC) Collaborative Research Network. Using data from 732 locations in 43 countries around the world it shows for the first time the actual contribution of human-made climate change in increasing mortality risks due to heat.

Overall, the estimates show that 37% of all heat-related deaths in the recent summer periods were attributable to the warming of the planet due to anthropogenic activities. This percentage of heat-related deaths attributed to human-induced climate change was highest in Central and South America (up to 76% in Ecuador or Colombia, for example) and South-East Asia (between 48% to 61%).

Estimates also show the number of deaths from human-induced climate change that occurred in specific cities; 136 additional deaths per year in Santiago de Chile (44.3% of total heat-related deaths in the city), 189 in Athens (26.1%), 172 in Rome (32%), 156 in Tokyo (35.6%), 177 in Madrid (31.9%), 146 in Bangkok (53.4%), 82 in London (33.6%), 141 in New York (44.2%), and 137 in Ho Chi Minh City (48.5%). The authors say their findings are further evidence of the need to adopt strong mitigation policies to reduce future warming, and to implement interventions to protect populations from the adverse consequences of heat exposure.

Dr Ana M. Vicedo-Cabrera, from the University of Bern and first author of the study, said: “We expect the proportion of heat-related deaths to continue to grow if we don’t do something about climate change or adapt. So far, the average global temperature has only increased by about 1°C, which is a fraction of what we could face if emissions continue to grow unchecked.”

Global warming is affecting our health in several ways, from direct impacts linked to wildfires and extreme weather, to changes in the spread of vector-borne diseases, among others. Perhaps most strikingly is the increase in mortality and morbidity associated with heat. Scenarios of future climate conditions predict a substantial rise in average temperatures, with extreme events such as heatwaves leading to future increases in the related health burden. However, no research has been conducted into what extent these impacts have already occurred in recent decades until now.

This new study focused on human-made global warming through a ‘detection & attribution’ study that identifies and attributes observed phenomena to changes in climate and weather. Specifically, the team examined past weather conditions simulated under scenarios with and without anthropogenic emissions. This enabled the researchers to separate the warming and related health impact linked with human activities from natural trends. Heat-related mortality was defined as the number of deaths attributed to heat, occurring at exposures higher than the optimum temperature for human health, which varies across locations.

While on average over a third of heat-related deaths are due to human-induced climate change, impact varies substantially across regions. Climate-related heat casualties range from a few dozen to several hundred deaths each year per city, as shown above, depending on the local changes in climate in each area and the vulnerability of its population. Interestingly, populations living in low and middle-income countries, which were responsible for a minor part of anthropogenic emissions in the past, are those most affected.

In the UK, 35% of heat-related deaths could be attributed to human-induced climate change, which corresponds to approximately 82 deaths in London, 16 deaths in Manchester, 20 in West Midlands or 4 in Bristol and Liverpool every summer season.

Professor Antonio Gasparrini from LSHTM, senior author of the study and coordinator of the MCC Network, said: “This is the largest detection & attribution study on current health risks of climate change. The message is clear: climate change will not just have devastating impacts in the future, but every continent is already experiencing the dire consequences of human activities on our planet. We must act now.”

The authors acknowledge limitations of the study including being unable to include locations in all world regions — for example, large parts of Africa and South Asia — due to a lack of empirical data.

Depression is a common condition in middle-aged and older adults, and it can contribute to a variety of mental and physical problems. Previous research has found a link between depressive symptoms and rapid kidney function decline in patients with chronic kidney disease (CKD). To look for a potential link in adults with normal kidney function as well, a team led by Xianhui Qin, MD (Nanfang Hospital, Southern Medical University, in China) examined information on 4,763 individuals with healthy kidneys when they enrolled in the China Health and Retirement Longitudinal Study (CHARLS).

At the start of the study, 39% of participants had high depressive symptoms, and during a median follow-up of 4 years, 260 (6%) participants experienced rapid kidney function decline. There was a significant association between depressive symptoms at the start of the study and rapid decline in kidney function during follow-up. Participants with frequent depressive symptoms were 1.4-times more likely to experience rapid kidney function decline than participants with infrequent depressive symptoms, after adjustments.

“CKD is a leading risk factor for cardiovascular disease, kidney failure, and mortality worldwide. Therefore, the identification of more modifiable risk factors may possibly reduce the huge burden of CKD and its related complications by leading to early detection and prevention,” said Dr. Qin. “While our study does not show causality, it demonstrated that high depressive symptoms were significantly associated with rapid decline in kidney function among Chinese adults with normal kidney function. If further confirmed, our data provide some evidence for depressive symptom screening and effective psychosocial interventions to improve the prevention of CKD.”

An accompanying Pantiet Voice article provides the perspective of a two-time kidney transplant recipient with an American-Born Chinese background.

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Materials provided by American Society of Nephrology. Note: Content may be edited for style and length.