Adaptations to endurance running during human evolution
From scavengers to hunters
About 2 million years ago, the climate in East Africa became even drier and more variable, and more and more grazing animals became widespread. In the genus Homo, there was continually increased selection pressure for abilities that enabled improved yields of animal food. With the appearance of the species Homo erectus around 2 million years ago, these abilities were apparently better developed than in Homo habilis. As a result, our ancestors gradually evolved from scavengers to hunters.
What abilities did Homo erectus have to have had to hunt savanna grazers? How could Homo erectus compete with the specialized predators? After all, they didn't have large, sharp fangs, and at that time they apparently didn't have any sophisticated hunting weapons, such as bows and arrows or spears, to be able to kill animals from a safe distance or from a hiding place.
Ideas?
Videos:
How humans evolved to be the best runners on the planet
Endurance Running Hypothesis�(Youtube Link)
Why Your Body Is Built To Run Long Distances
Human Spark - Runninng = Big brains?
Questions for discussion in class :
What features of our body and physiology seem to be adjustments to endurance running?
Why could these adaptations to endurance and long-distance running have come about in the course of our evolutionary history?
Adaptations for endurance running
The skeleton and musculature of Homo erectus indicate that they were adapted not only to upright walking, but also to endurance and long-distance running. For example, the neck ligaments, the gluteal muscles, the knee joints, the long legs, the Achilles tendon, the short toes and the curved soles of the feet are adapted to the challenges of running. The need for thermoregulation while running also led to a reduction in body hair and development of sweat glands, as well as a protruding nose to make heat release through sweating and breathing more efficient.
Homo erectus left Africa and explored new regions
Various features of the skeleton and muscles of Homo erectus that primarily perform functions for running.
Costs?
(energy, time)
Benefits?
(Functions for survival and reproduction)
Challenges for survival and reproduction
Why run?
Running uses much more energy than walking, and the key to the survival and reproductive success of living things is usually energy efficiency, since energy is limited. To explain why the body specialized in endurance running over the course of evolution despite its energy expenditure, endurance running must have given our ancestors a survival and reproductive advantage.
Those who were more motivated to run, could run better and longer, were less likely to get injured while running, or used less energy to run survived better and had more offspring than those who couldn't do this as well. So what were the benefits of this behavior?
Scientists suspect that endurance running was a way to tire out prey animals and then kill them by throwing stones, especially at a time when Homo erectus did not yet have any tools or hunting weapons to kill animals from further distances. In addition, endurance running expanded the available range from which more resources could be obtained. In fact, it currently seems that Homo erectus was also the first species of the genus Homo to leave the African continent.
The relationship between physical and cognitive traits
Physical activities such as running and throwing, but also making and handling tools, not only led to adaptations in physical body structures that made running, throwing, and tool handling better, more efficient, and easier. Physical activity was also linked to changes in the brain and cognitive abilities.
Natural selection of physical structures that are beneficial for behavior
Natural selection of brain activity and cognitive abilities that are beneficial for behavior
Stimuli that trigger behavior
Natural selection of genes that influence brain function
Natural selection of genes that influence physical structures
Causal map: Biotic, abiotic and social environmental factors may trigger certain behaviors in animals. When the behavior is important for survival and reproduction, there will be selection pressure for bodily structures and mental abilities that are advantageous for the behavior and its initiation. Genes that are involved in the development of these body structures and mental abilities are in turn selected and passed on to the next generation. The actual behavior continues to be triggered in the next generation by biotic, abiotic and social environmental factors, e.g. through the presence of similar food sources and environmental stimuli, and imitation of others in the social environment.
In species adapted to running, increased physical activity increases the production of neurotransmitters and hormones in the brain and body which influence endurance, thermoregulation, pain sensitivity, motivation, and well-being. In physical movements that require precision and coordination, there is a strong selection pressure for the connectivity and activation of brain regions responsible for these skills. In many animal species, these appear to be particularly regions in the left hemisphere of the brain.
Endurance running, neurotransmitters and the brain
After a long run and similar endurance sports, people can often feel a so-called “runner’s high” - a feeling of happiness, euphoria, inner satisfaction and balance, positive mood and reduced sensitivity to pain. The reason for this appears to be an increased production of certain hormones and neurotransmitters during and after such physical activities. Neurotransmitters are molecules produced in the body that are responsible for the transfer of information between nerve cells and other cells. Neurotransmitters thereby influence mental and motor abilities and mental states. Neurotransmitters released during increased physical activity include dopamine, serotonin and endocannabinoids.
Endurance sports also increase the blood supply to the brain and thereby improve brain performance, especially in long- and short-term memory, the ability to concentrate, react and learn. Endurance sport ultimately leads to a lasting improvement in brain functions over a longer period of time over the course of a lifetime.
However, in today's environmental conditions, we no longer rely on running long distances for our survival. This leads to a lack of physical activity, and this in turn can lead to physical and mental health problems.
The combined activity of these neurotransmitters is responsible, among other things, for the reward system in the brain. It keeps us motivated to achieve goals, try new things, explore new areas, and solve new problems. When we are successful, we experience a feeling of happiness or “kick” that reactivates the reward system and motivates us for future efforts. Dopamine is also involved in thermoregulation and coordination of movements. Serotonin, endocannabinoids and the hormone endorphin increase mood and reduce pain sensitivity. All of these effects increase endurance and motivation to run.
Lab mice bred for increased endurance while running showed higher dopamine production in the brain and higher motivation to run than lab mice with low endurance. In humans and dogs (which are also adapted to running), the production of endocannabinoids increases after an endurance run. This effect is not seen after light walking and is not seen in animal species that are not adapted to running. Biologists therefore think that increased production of these neurotransmitters arose through natural selection as an adaptation to endurance running in our species. However, this increased production of neurotransmitters only happens when living beings actually carry out this behavior during their development.
Concentration of endocannabinoids in the blood of humans, dogs and ferrets (a species of marten) before and after running and walking.
Note: Have students complete the causal map by leaving out some parts (text boxes, arrows) or providing them to students to create the diagram.
Enables/allows/facilitates/ favors the development of ...
Favors natural selection of...
Environmental conditions in the savanna
Meat-based diet
Endurance running
Body structures that enable endurance running
Brain activity that enables endurance running
Genes that influence the development of brain activity and body structures that enable endurance running
Environmental conditions in the savanna
Meat-based diet
Endurance running
Body structures that enable endurance running
Brain activity that enables endurance running
Genes that influence the development of brain activity and body structures that enable endurance running
Others engaged in running
References
Bramble, D. M., & Lieberman, D. E. (2004). Endurance running and the evolution of Homo. Nature, 432(7015), 345–352. https://doi.org/10.1038/nature03052
Raichlen, D. A., Foster, A. D., Gerdeman, G. L., Seillier, A., & Giuffrida, A. (2012). Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the “runner’s high.” Journal of Experimental Biology, 215(8), 1331–1336. http://doi.org/10.1242/jeb.063677
Schulkin, J. (2016). Evolutionary Basis of Human Running and Its Impact on Neural Function. Frontiers in Systems Neuroscience, 10(July), 1–10. https://doi.org/10.3389/fnsys.2016.00059
Waters, R.P., K.J.Renner, R.B.Pringle, Cliff H.Summers, S.L.Britton, L.G.Koch, & J.G.Swallow (2008): Selection for aerobic capacity affects corticosterone, monoamines and wheel-running activity. Physiology & Behavior, 93 (4–5), 1044-1054. https://doi.org/10.1016/j.physbeh.2008.01.013
Author: Susan Hanisch
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