Photo by Jason Hickey, distributed udner Creative Commons (CC BY 2.0).
By Jalees Rehman
The history of humankind is also the history of controlling fire. Myths and folklore from all over the world attest to the central role that fire has played in our history. Matarisvan in the Hindu Rig Veda and Coyote in Native American legends are credited with gifting fire to humans. The Greek legend of Prometheus recounts how Prometheus – always looking out for human welfare and development – angered Zeus by sharing the secret of fire with humans. As a punishment for his humanist deed, Prometheus was chained to a rock. He endured the pain of an eagle preying on his liver, which would regenerate each day and thus perpetuate the daily trauma of having part of his liver ripped out by an eagle. The magnitude of this Promethean torment only underscores the significance that the Ancient Greeks attributed to the usage of fire by humans.
We do not need to rely on ancient myths to understand the importance of fire in our history. The discovery of burned bones and plant remains in a cave in South Africa suggests that our hominid ancestors used controlled fire at least one million years ago, and there is ample evidence for regular fire usage approximately 350,000 years ago. Was controlled fire just one of the many tools that hominins harnessed and used or was fire essential for the evolution of our species? There are obvious benefits to using fire such as staying warm when it is freezing cold outside or fending off potential predators. The primatologist Richard Wrangham famously formulated the “cooking hypothesis” which stated that central benefit of fire usage was that it enabled hominins to cook their food. Cooked food allowed our ancestors to increase the amount of energy their bodies could extract from food. Instead of wasting energy trying to digest raw food, fire-controlling hominins could utilize this additional energy to grow bigger brains and evolve cognitively.
An even more intriguing perspective for the indispensable role of fire has been put forward by the primatologist Frances Burton from the University of Toronto in her book, aptly titled, “Fire: The Spark That Ignited Human Evolution”. Burton does not discount that fire provided warmth and a means for cooking but she proposes that the key benefit our ancestors derived from controlling fire was that it allowed them to generate light. Instead of having to rely on natural sunlight, hominins used fire as a light source at night to artificially extend the day. Burton suggests that the light emitted from campfires changed the hormonal patterns of our ancestors. It suppressed the hormone melatonin which is released by the pineal gland in our brain at night and functions as an important regulator of our internal biological clock. According to Burton, the changes in hormonal patterns by campfires liberated our ancestors from the natural light-dark cycles and seasonality and increased their ability to reproduce.
As intriguing as Burton’s idea is, there is little scientific evidence to back up the notion that light emitted by the campfires of our ancestors was sufficient to propel human evolution forward by affecting internal biological clocks. Humans, like other animals and plants, have an internal biological timekeeping system called a circadian clock. The name “circadian” is derived from “circa” = ‘approximately” and “dian” = “one day” and refers to the fact that our internal clock runs at a period of approximately 24 hours, mirroring the 24 hour day/night cycle of the earth. The internal circadian clock allows our body to anticipate the external time of the day. Our body temperature, hormones and many other important processes in the body would keep on cycling in a 24 hour rhythm even if we were to spend a few days in continuous light or in continuous darkness.
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