Why Did the Ancestors of Humans Evolve an In-Built Fear of Snakes and Spiders Around 40–60 Million Years Ago? — Here’s What Researchers Suggest

Have you ever looked at a snake or a spider and immediately felt a tingling sensation in your whole body? It turns out it’s not just a few of us who feel this way, but rather, the fear of snakes and spiders is common in a large human population. Researchers think that it is also not unique to us, and our ancestors a long time ago instinctively feared them too.

However, how exactly did this in-built mechanism pass down to us, and why did it survive for this long, even if the threat is not as persistent anymore? Moreover, are we all born fearing snakes and spiders already? Or is it a learned experience from our parents and other close peers? Let’s dive deep into the past and explore all these ideas and questions in this article.

Evolutionary Pressure — Why Fear of Snakes and Spiders Might Have Helped Survival

The modern human species, Homo sapiens, is part of a group of other species called hominins. It includes all other human relatives and direct ancestors from when our lineage split from chimpanzees around 6 to 7 million years ago. Some examples of other species in this group are Homo erectus, Homo heidelbergensis, and Australopithecus.

It is likely that these relatives and ancestors may have also possessed a fear of snakes and spiders. This is because experts estimate that this innate defensive mechanism began around 40 to 60 million years ago, around the same time when our primate ancestors were coevolving with them.

During this period, small mammals and Old World primates were living in a world full of threats. They existed in the same environments as big predators, but also smaller animals that could possess an ability to incapacitate them quickly in ways other than just brute strength, namely through the injection of venoms. This could be the case for the ancestors of snakes and spiders.

For them to survive, they had to know how to live along with these creatures in the woodlands or forest areas. That could mean an early detection of the threat, since snakes and spiders would consistently pose a danger to their lives. This phenomenon may have created an evolutionary pressure that allows individuals capable of recognizing and reacting to them to be more likely to survive and pass on their genes.

Additionally, since this threat may not have gone away over the last tens of millions of years following its estimated timeline of origin, the hominins may have still retained the same defensive mechanism or fear of snakes and spiders.

Read more: National Geographic

How Our Brains Are Wired to React Quickly

You Were Born to Fear Snakes - Here’s Why

For 40 to 60 million years, our primate ancestors and hominin lineages may have been developing their brains as influenced by this fear of snakes and spiders. Since the humans who could recognize and react quickly after seeing these creatures may be more likely to survive and pass on their genes, their brains may have also adapted over time to refine this defensive mechanism.

This means that our brains could have developed special systems in our minds to detect snakes and spiders as fast as possible. Some evidence of this in research was that parts of the brain, like the Amygdala, reacted faster when images of snakes and spiders were shown, compared to other animal species. In an experiment, humans could spot photos of these creatures quicker than a flower or a mushroom.

This rapid detection tells us that our brains are wired to notice these creatures faster than other objects in our environment. Mostly because of our ancestors’ survival needs to quickly detect them, as one bite with venom could easily mean they would be incapacitated.

Read more: PubMed Central

Innate vs. Learned — Do We Come with the Fear, or Do We Get It?

So, are we all born with an innate fear of snakes and spiders if our primate and hominin ancestors may have developed them in order to survive and pass on their genes? Researchers actually have a few theories about this concept, with some suggesting that babies have them since they are born.

Infants do not necessarily scream in fear after seeing snakes or spiders, but their pupils have been observed to dilate, and they have some form of reaction. This may be a result of this threat existing for so long that evolution may have built an innate defensive mechanism toward it.

Other researchers, however, believe that these may be influenced by their parents, guardians, or other people surrounding the infants. For example, kids whose parents already have a great fear of snakes and spiders may have passed it to their children via learned behavior or culture.

The answer is most likely both of them. We may already have the built-in mechanism to recognize these threats, but the culture and other humans’ behavior of fearing them could have exacerbated this feature of humans.

Read more: The Human Evolution Blog

What This Means for Modern Humans

Why are we so afraid of snakes and spiders? A psychologist answers

Humans in the modern world do not usually encounter deadly snakes or spiders on a daily basis in their environments, but still, a few people have carried on this fear, even developing some phobias. Ophidiophobia refers to the overwhelming fear of snakes, and Arachnophobia is for spiders and other arachnids.

These features are most likely a leftover of the survival system that our ancestors needed in their environments and the world they lived in. Compared to millions of human history and the primates’ lineage, Homo sapiens are relatively recent. Even just 50,000 to 70,000 years ago, we were still living in Africa, before migrating to other continents. This is a place where those mechanisms could have also been needed by our direct ancestors of the same species.

This is a reminder that our past is still continually shaping who we are today. Maybe in this world we live in right now, the threat of snakes and spiders is not as persistent anymore, so our reaction is usually stronger than necessary. But, it does not mean that it is totally useless; we may never have gotten to where we are today evolutionarily if our ancestors did not develop these mechanisms. So, we have to accept that these fears may be a part of us in the past, in the present, and could be in the future.

Author's Final Thoughts

So, why did our ancestors develop a fear of snakes and spiders that up until today we still feel? This is most likely because the primates that lived around 40 to 60 million years ago may have needed to coexist and coevolve with these creatures. Thus, creating a selection pressure, where those who are capable of recognizing and reacting to the threat quickly were the ones who were more likely to survive and pass on their genes.

Spotting a spider or a snake may just trigger a fear or phobia today, but before, it could literally be life or death. So, over time, our primate brains to our hominin bodies may have developed this mechanism even further. This could have resulted in humans today having an overwhelming reaction to seeing snakes or spiders. But this fear is not irrational; it’s just a trace of our long history of life on this planet, inherited from our lineage and very own ancient ancestors.

Read next: How Has Living in Crowded and Densely Populated Communities Changed Humans Over the Last 10,000 Years? — Here’s What Researchers Discovered

References & Further Reading

Isbell, L. A. (2006). Snakes as agents of evolutionary change in primate brains. Journal of Human Evolution. https://doi.org/10.1016/j.jhevol.2005.12.012

Van Le, Q., Isbell, L. A., Matsumoto, J., Nguyen, M., Hori, E., Maior, R. S., et al. (2013). Pulvinar neurons reveal neurobiological evidence of past selection for rapid detection of snakes. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.1312648110

LoBue, V., & DeLoache, J. S. (2008). Detecting the snake in the grass: Attention to fear-relevant stimuli by adults and young children. Psychological Science. https://doi.org/10.1111/j.1467-9280.2008.02081.x

Hoehl, S., & Pauen, S. (2017). Infants react with increased arousal to spiders and snakes. Frontiers in Psychology. https://doi.org/10.3389/fpsyg.2017.01710

Fry, B. G., Vidal, N., Norman, J. A., et al. (2006). Early evolution of the venom system in lizards and snakes. Nature. https://doi.org/10.1038/nature04328