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How does our Climate impact Human Evolution?

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How does our Climate impact Human Evolution?

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This has been a long speculated question, and many scientists today are still unsure of the precise answer! Climate and evolution have worked together to make lots of different transformations on our planet.1 Most scientists hypotheses conclude that climate driven environmental changes have lead to speciation, bipedality, larger carnival capacity, behavioral adaptations, and new cultural ideas.2,3 However, it is difficult for science to present the direct link between climate change and human evolution. As Dr. Rick Potts said, the tendency for an environment to change is what has heavily impacted human evolution.⁴ Most scientists ask themselves the question, how do we relate paleoclimatic evidence in marine life and terrestrial life with the emergence of our Genus Homo? To find the answer to this question, scientists needed more than just data from rocks, so they explored under the ocean. There are libraries full of records of the oceans core, and scientists use their expert eyes to determine whether layers are from wet or dry years.⁵ This question has been difficult to answer, but scientists have made lots of progress!46

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.
² "Climate Effects," Smithsonian National Museum of Natural History.
³ National Academies Press, "Understanding Climate's Influence on Human Evolution," National Center for Biotechnology Information, last modified 2010, https://www.ncbi.nlm.nih.gov/books/NBK208104/.
⁴ "Climate and Human Evolution," PBS, https://illinois.pbslearningmedia.org/resource/clim10.sci.ess.watcyc.evoclimate/climate-and-human-evolution/.
5 "Climate and Human," PBS.
⁶ "Climate Effects," Smithsonian National Museum of Natural History.

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When trying to prove the connection between climate change and human evolution, scientists typically use three points to determine whether data is accurate. The first step is having a clear definition of synchronous. This means making sure that when comparing data, the synchronous data actually accurately and timely relate to each other. The next step is to determine the mechanism that transmits climatic cause to evolutionary effect. The final step is to find lots of proxy evidence that support these interpretations. Following all these steps is the best way scientists are able to determine evidence's credibility in proving their cause-effect hypotheses!1
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1 Anna K. Behrensmeyer, "Climate Change and Human Evolution," Science 311, no. 5760 (January 2006): https://www.jstor.org/stable/3843397.

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Major evolutionary events defined humans behaviors, bipedalism, use of stone tools, emergence of homo sapiens, and culture. Scientists have found that a lot of these evolutionary events happened at the same time as climate changes in Africa and Europe happened. When creating their research report, the National Research Council emphasized the critical resources for human survival, water and vegetation. In a lot of the experiments performed to prove the link between climate and evolutionary change, these are the resources scientists must pay special attention to!1

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1 National Academies Press, "Understanding Climate's Influence on Human Evolution," National Center for Biotechnology Information, last modified 2010, https://www.ncbi.nlm.nih.gov/books/NBK208104/.

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National Research Council Report on Climate Change's Influence on Evolution

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National Research Council Report on Climate Change's Influence on Evolution

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The National Research Council created a report about faunal and paleoclimate evidence to find climate change’s influence on evolution. They found that large climate shifts had high rates of faunal turnover, and that speciation and behavioral changes seem to be connected to African climate change in the past 5 million years. When studying African dry-wet cycles, scientists found that faunal changes often happened at the same time. Although this variability is unlikely the only selection factor, it concludes that more climate variability led to large climate and ecological shifts. Human adaptations, such as bipedalism and stone tool making, are just some of many trains that have distinguished us from other species!1

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1 Peter B. DeMenocal, "Climate and Human Evolution," Science 331, no. 6017 (February 2011): http://www.jstor.org/stable/25790209.

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Comparing Marine Core Records and Land Core Records

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Comparing Marine Core Records and Land Core Records

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One of the ways that scientists worked to tackle this difficult question was by comparing the marine core records and land core records on a local and global scale. They also compare these records to the human evolution timeline, to get a closer look at what major environmental changes happened at the same time as evolutionary ones. Paleoclimatic proxy evidence is more individual to a specific place’s climate and is therefore harder to use globally. This makes it difficult to determine what has enough data to prove a link between climate change and a major evolutionary change. Climate is also only one of many factors impacting evolution, meaning there are other factors to consider when comparing data!1

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1 Anna K. Behrensmeyer, "Climate Change and Human Evolution," Science 311, no. 5760 (January 2006): https://www.jstor.org/stable/3843397.

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The Savanna Hypothesis believes that tool-making and upright walking are related to drier habitats and more grasslands. People who follow this hypothesis think that these adaptations began in the African savanna!1, 2

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.
² Michon Scott, "Climate and Human Evolution," Climate.gov, last modified November 9, 2016, https://www.climate.gov/news-features/climate-and/climate-and-human-evolution.

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The Variability Selection Hypothesis states that human evolution is shaped by environmental instability. This hypothesis was developed by Dr. Rick Potts, who believes that human traits evolved because environmental uncertainty forced humans to adjust and adapt. Since the genus Homo belonged to many different environments, his hypothesis  takes into account the variability in all types of ecosystems. The different ways homo learned to adjust to shifting environmental conditions were through natural selection and evolving structures. Natural selection favors one genetic variant over another. Natural selection is typically thought of as "survival of the fittest", however, natural selection has also helped those able to adapt to the changing climate! Evolving structures additionally helped us by altering our behaviors to best survive in new conditions. 1,2

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.
² Michon Scott, "Climate and Human Evolution," Climate.gov, last modified November 9, 2016, https://www.climate.gov/news-features/climate-and/climate-and-human-evolution.

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Australopithecus afarensis, also known as our dear friend Lucy, had humanlike hip bones, knee joints, longer arms, and flexible feet for climbing and walking.¹ This type of body structure allowed for moving around in diverse habitats.2 Some of these features, especially bipedalism, are likely adapted traits and set us apart from other primates!

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1 National Academies Press, "Understanding Climate's Influence on Human Evolution," National Center for Biotechnology Information, last modified 2010, https://www.ncbi.nlm.nih.gov/books/NBK208104/.
2 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.

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Stone tool making shows how humans adapted to their surroundings and became toolmakers. Adjusting to their environments allowed them to make tools that made it easier to access more foods. This skill, that slowly developed and improved over time, helped with altering diets throughout environmental change. When resources were short or climate changed, humans were able to use their toolmaking skills to help them in difficult situations! For some others, environmental change was the cause of the extinction of their species. Our ability to adapt and learn new skills made it easier for us to adjust to change! 1

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.

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Evolution has happened at the same time as cooling, drying and more versions of climate fluctuations happened. One of the important ways to find the link of these things is by looking at the record of oxygen isotopes over time. This graph shows the changing temperature and glacial ice over time. Scientists have concluded that there is much greater environmental variability in later evolution stages!1

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.

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Larger brains also likely resulted due to climatic shifts. In the graph below, we see that with greater climate fluctuation, there was a greater increase in brain size. Scientists believe this is because great global climate fluctuation forces humans to change and think of ways to adapt to the new environmental conditions. Larger brains have more space to process and store information, solve abstract problems, and produce versatile solutions to environmental change. This ultimately lead to more interactions between different groups of people, because people were learning it is important to find help from others when resources are low. Soon, various groups of people began trading and exchanging ideas. Social ties and the exchange of gifts between these groups helped build strong relationships during environmental uncertainty!1

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1 "Climate Effects on Human Evolution," Smithsonian National Museum of Natural History, last modified September 1, 2020, https://humanorigins.si.edu/research/climate-and-human-evolution/climate-effects-human-evolution.