Summary: The understanding of evolution is key to all branches of modern biology. The interplay between replicators (genes), vehicles (the body) and the environment explains why some species have adapted to a particular environment and could not thrive somewhere else. Moreover, stress is what indirectly leads to adaptation. As a consequence, the organism might live long enough to reproduce. However, competition is a crucial condition of natural selection and eliminates species that do not adapt.
Nothing in biology makes sense except in the light of evolution.Theodosius Dobzhansky (geneticist).
You are a product of natural selection. However, your response to stress contributes to whether you will continue to exist (by ‘you’ I mean your genes). The link between natural selection and stress might seem distant but allow me to take you through the facts.
There are two concepts to have in mind:
- Genes, also known as ‘replicators’, are the primary unit of selection and heredity. Thus, in the process of reproduction, the genetic information will be duplicated and then passed on, forming 50% of your offspring (aka children).
- A vehicle is the body protecting the genes (e.g. the human body, your dog’s body, a tree’s trunk and leaves or the cell membrane of a bacteria). Each species uses different vehicles to protect and pass on their genetic information. Some species (humans) can live in more than one type of environment; others cannot (that is why you do not find kangaroos in Alaska)
Let me unpack this for you.
Your parents’ genes contain the necessary instructions for your cells to produce particular proteins. These proteins will replicate some of their characteristics (e.g. height). These characteristics will form your body (i.e. the vehicle) and determine your chances of surviving, reproducing and passing on your genes in a given environment.
For instance, a bird with a fragile beak living in an environment where there are only hard-shell nuts is unlikely to thrive. Probably, stronger, larger beak birds can crack and eat those hard-shell nuts. As a result, these strong-beak birds will stay healthy and reproduce. Whereas, the fragile-beak birds will either die of hunger or adapt (e.g. eat something else). These possibilities (die or adapt) indicate there is an evolutionary pressure acting directly on the population of birds making them stressed. Researches, Grant & Grant, have reported a real example involving birds. The Galapagos finches (Geospiza magnirostris) has developed into three other species.
The bird example has a hidden message that applies to every species on the planet (including humans) and links stress with natural selection: there are limited resources available. The most critical resources are food, shelter and mating partners. The lack of resources, triggers stress (e.g. hunger) in each bird. Thus, each bird will seek new alternatives to survive by adaption (e.g. moving to a different area). Therefore, competition is a necessary condition for natural selection to exist, and stress is the body’s reaction to ensure survival.
The role of stress.
Stress is a survival mechanism characterised by “an organism’s reaction to a stressor”. Stressors shifts the organism (e.g. humans) from its optimal physiological state. There are several type of stressors:
- A biological agent (e.g. a influenza virus).
- A chemical agent (e.g. alcohol).
- An environmental condition (e.g. hot weather)
- An external stimulus (e.g. a being bullied)
A real-life example involves an adult’s average heart rate in resting-state, which is between 60-100 beats per minute. However, imagine you are walking home at night, and someone tries to attack you. What happens? Your heart rate will immediately increase. The up-regulated heart rate will ensure the delivery of oxygen to your legs, generating enough energy to start running and potentially avoiding the attack. Once you are safe at home, your body restores its stable physiological state, and you are no longer in stress. This case is a simple example of how stress works for you and enables a vehicle to pass on its replicator to the next generation. Scientists and writers often refer to this survival mechanism as the fight or flight response, a concept put forward by Walter Cannon in 1915.
However, there are ways in which stress works against you. For example, sustained psychological stress (e.g. a frustrating job) may develop into mental illnesses, such as depression. But there will be a post dedicated to psychological stress.
Key takeaways: Stress is key to ensure survival under natural selection. It can literally save your life. Also, stress is essential to evolution by adaptation. Hopefully, you will begin to view human behaviour from a scientific point of view, which offers several insights to your day-to-day life.
Dawkins, R. (2006). The selfish gene. 30th anniversary ed. Oxford ; New York: Oxford University Press.
Foley, R. A., & Lewin, R. (2013). Principles of human evolution. John Wiley & Sons.
Grant, Peter R., & Grant, B. Rosemary (2008), How and Why Species Multiply: The Radiation of Darwin’s Finches, Princeton University Press
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