The change is not as likely to happen as previously thought

Exercise: The change cannot be made as previously thought

During the dry season, the water leaves to melt behind the trona crystals, which rise in the shores of Lake Magadi, the southernmost lake of the Kenyan Rift valley. A spinning rig used in the study can be seen climbing over the dry lake mat. Found: Andrew Cohen / University of Arizona

A new study that combines climate data with the biological histories of large mammals that lived in Africa 4 million years ago is questioning a long -standing hypothesis that is constantly changing the climate in as a major driver of evolutionary change in mammals, including human ancestors.

Published in a journal Proceedings of the National Academy of SciencesThe study will provide an African continental-wide synthesis of environmental change during the Plio-Pleistocene, a period in Earth’s history that lasted about 5 million years and included the last ice age about 20,000 years ago.

The study found that the atmosphere at that time in the mirrors changed the Earth’s orbit and the way it relates to the sun, as predicted by a natural phenomenon called Milankovic cycles. These orbits show our Earth different patterns of solar eclipse, resulting in recorded, cyclical effects on Earth’s atmosphere at different frequencies.

Researchers have found that different levels of snow and ocean temperatures have taken a long time to increase in environmental diversity across Africa. However, the results did not provide a significant relationship between environmental change and the onset or end points, indicating that environmental and behavioral differences were not significant. the search for meaning, an idea that has been much debated in the scientific community.

The notion that long -term exposure to a cold or dry state is the reason for human development going back to the time of Charles Darwin, according to the paper’s first author, Andrew Cohen, is a University Honors Doctor in the Department of Education at the University of Arizona. of Geosciences and the Department of Ecology and Evolutionary Biology. A major change came in the late 1990s, with the introduction to the scientific community of the revolutionary choice hypothesis.

“The idea here is not just to point out that climate change is important as a driver for evolutionary innovations in the hominin lineage, but the diversity of the environment and conditions. now, “Cohen explained. “To our forefathers who are in a state of rapid change, this hypothesis is that they need to be more resourceful and able to manage many different things, that is, be guided in many ways. new and everything else is gone. “

In the present study, researchers analyzed samples taken from sediment fragments from lakes, ocean floors and landforms from 17 locations around the African continent and the all around. Environmental data is based on analyzing data from pollen, fossilized algae, soil, leaf waxes, soil isotopes and other physical resources that provide clues about plant species and environmental standards at the site where it is located. To combine data from these different stories and mock the underlying nature of climate change, Cohen said the company will overcome a major challenge: how to calculate the difference and compare it from one reference point to another.

Exercise: The change cannot be made as previously thought

Workers use a spinning wheel to collect samples of internal sediments from deep down. Found: Andrew Cohen / University of Arizona

“It doesn’t matter because you’re in stories on the other side of things like fossil pollen telling you about plant evolution, someone telling you about “changing the sea levels, and someone will tell you about the movement of the soil into the ocean,” he said. said. “We need a way to not just look at one story but capture these different types of directions so that we can differentiate the nature of change.”

To do this, the researchers developed statistical methods that allow them to “compare earthquakes and oranges,” Cohen explains, and provide historical data in “bins.” of times 20,000, 100,000 and 400,000 years. Once the individual data of the conversion numbers in each bin has been recorded, the team can “stack” them and calculate the amount of variance for each period.

The geological data were closely compared with the biological history of large mammals – primarily bovids, a family related to antelopes and other large herbivores – from East Africa. Researchers have looked at large herbivores because herbivores from human ancestors cannot be used.

“I’m not saying you can put everything (hominin diamonds) back in a shoe box, but they aren’t the same as normal ones,” Cohen said, “so we decided to take a look at the other creatures with a better fossil history, because there is no reason to think that only our immediate family, our hominin ancestors, will be affected by climate change and diversity.

“If climate change is a major driver of evolution, it should be a driver and growth of other large mammals, as well,” he said. “Think, for example, of the polar bear and the impact of climate change today.”

The authors used an approach borrowed from modern wildlife biology to illustrate a point held by paleontologists: the incompleteness of the fossil history, as reported by the author. second of the study, Andrew Du, with a block of Swiss cheese. If one grinds the sample through salt, there will be gaps from where the base touches the second layer of cheese. Similarly, there are gaps in the history of fossils of some kind – times when fossils were not known — that are linked to when fossils were found. This is very difficult to establish exactly when a particular style emerged in the history of coal and when it ended.

To avoid this limitation, Du used a technology called capture, marking and re -recording, which is often used by animal life experts when they look at animal populations: Back the capture of an animal was signaled to be seen and released back into the forest. During a later study, the scientists compared the number of animals trapped. Asking for statistics, they can get an idea of ​​the size and nature of the population.

Exercise: The change cannot be made as previously thought

All mammals, such as these wildebeest, were caught in a pond in the Serengeti National Park in northern Tanzania, when they migrated to Africa and left behind a plethora of fossils. Found: Andrew Cohen / University of Arizona

Du, an assistant professor in the Department of Anthropology & Geography at Colorado State University, explained how technology works in fossil systems.

“We say we see a new type of rock in the history at one time, and then we see a different type of rock from the same type the second time, we disappear the third time, but we know “We’ll meet again four times,” he said. “What that tells us is that even though we don’t know what it means the third time, we know it’s all around. It’s good when it comes to choosing the speciation number and the finish.”

Combining all of this data allows the researchers to compare the characteristics of environmental diversity and how it relates to the onset of mammal species and endpoints.

“Overall, there has been a long process over the past 3.5 million years of increasing environmental diversity,” he said. “That kind of follows an increase in snow levels and sea temperatures around Africa. On top of that, we see something else: When we enter the snowy years, we see the ups and downs; contemplating the sharpening and falling of the icebergs, and of that sort to follow Milankovic’s 400,000 -year cycle. “

In all cases, the history of origin and destruction among large herbivores, as well as hominin fossils, has been seen to be isolated from these different types of climate. While the authors acknowledge the validity of the differential choice hypothesis but work on different scales, they hope to encourage the scientific community to think about the differential choice hypothesis in a critical way, ” rather than accepting it as a teacher. how do we look at the fossil history of Africa, and the fossil history of mankind, “said Cohen.

“We’re not saying environmental diversity is important for human development, but the data we’ve gathered so far doesn’t match that idea,” he said. “If environmental change is as significant as it has been, we would expect to see that kind of long -term increase in change compared to evolutionary search in all aspects. , with hominins, but we don’t know that… ”


Earth’s environment depends on the diversity of the millennial climate


More information:
Plio-Pleistocene climate change in Africa and its consequences for mammalian development, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073 / pnas.2107393119.

Presented by the University of Arizona

Directions: Change cannot be reversed as previously expected, research (2022, April 11) found on 12 April 2022 from https://phys.org/news/2022 -04-climatic-variability-evolutionary-previously-thought .html

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