Background
Why are diseases like diabetes, heart disease, high blood pressure, Parkinson's, Alzheimer's, lactose intolerance, and allergies common among people today? Many of these diseases are on the rise in human populations around the world, and cancer is an increasing health problem that is familiar to almost everyone. Lately, a big newsmaker is the disease called obesity, because it is also becoming more common. Why do we gain weight fast, and why isn't it easy to lose weight? The book Zoobiquity, the Astonishing Connection between Human and Animal Health by Barbara Natterson-Horowitz, M.D., and Kathryn Bowers explains the similarities between human and animal diseases, such as our extreme weight gain and the obesity experienced by animals in the zoo. Diet pills, shots, and surgery give us some capacity to battle obesity, and for many people these approaches create false hope of completely repairing their weight gain. The latest trend is Ozempia often seen on mainstream television and described in social media. But what causes obesity to become a problem for humans in the first place? Immediately, we can guess this is caused by the foods we eat in modern times, which tend to have more calories, sugar and fat than many foods we used to eat earlier in human history. These foods can lead to weight gain, and also contribute to onset of other diseases, such as cardiovascular problems, diabetes, glucose intolerance, some cancers, musculoskeletal disorders, and high blood pressure (Natterson-Horowitz & Bowers, 2012). Humans and animals cannot afford to have issues with our vital organs, including the heart, liver, lungs, and kidneys because these organs are essential to make the human body healthy and to run properly.
What about diseases caused by pathogens such as viruses? This can also be explained by evolutionary medicine, beginning with ideas from scientists from the 1990s. “ In the 1990’s, George Williams and Randy Neese, followed by other, developed Darwinian (evolutionary) medicine, applying the principles of evolutionary biology to the broader question ‘Why do we get sick?’ “, (Johnson, 2022) In the time since, evolutionary medicine is becoming a separate dreading about evolutionary medicine, I learned that pathogens reproduce and evolve very quickly, whereas hosts like humans reproduce much slower and cannot rely on our evolution to keep pace with the changes happening in virus pathogens. Instead, we use our quickly changing immune system cells to fight against pathogens, but this is often not sufficient to do the job and increasingly modern medicine like vaccines have to be used. The thought that pathogens and bacteria are essential challenges to human medicine gave me the idea of balance.
Evolutionary Medicine
We listen to neighbors, and our colleagues at work speak about many medical issues such as allergies, being overweight, having high blood pressure, struggling with high cholesterol, being annoyed with skin irritation, confusion about having cancer, and not knowing there are different types of cancer. So, how does evolutionary medicine connect to this topic?
Evolution
In biology, living organisms appeared on Earth in the distant past, perhaps 4 billion years ago. Some organisms like bacteria have been around since the early days of life on Earth and are still here today. As time passed, the biodiversity of living organisms increased to include larger numbers of species, which became better suited to their specific environments. The ability to change over time to match environmental challenges holds for all living creatures on Earth, and today organisms continue to experience evolution by natural selection to better thrive and adapt to their environments. However, species that cannot adapt to finding food, protecting themselves, or in other ways to meet these challenges can become extinct.
The genetic change necessary to go from living in water to instead thriving on land requires very many genetic changes. Long ago, plants, animals and other life forms evolved traits that let them survive and reproduce in terrestrial habitats. But Futurity.org has an article that reminds how marine tetrapods, the group of animals that includes whales, dolphins, seals, and sea turtles, have moved from the land back to the oceans over the last 350 million years-requiring radical changes to their lifestyles, body shapes, physiology, and sensory systems. During this process, not all variants (genotypes) were successful. Imagine how certain dolphins with faster ability to move through water had adaptations that were advantageous compared to other members of their populations. The ones that survived had the genes which provided better ability to make offspring which were also successful. For example, dolphins have tails that are excellent for moving quickly through water to chase prey such as fish, replacing other variants that were less capable of fast movement through water.
Charles Darwin's famous idea of natural selection is based on his theory of this process of evolution, which states that the variants with better ability to survive and reproduce will cause the population to evolve and take on these successful traits. Darwin observed that birds’ beaks on the Galapagos Islands looked different than those of close relatives on the mainland, because different beak shape can evolve to use seeds and other food resources found on certain islands, a challenge in the bird’s environment (Johnson, 2022). Not only is it important to adapt by changing traits such as those useful for movement and obtaining food resources, but it is also important to consider how variants can be advantaged in interacting with other species, such as outsmarting their predators. To stay alive, a species must evolve defense attributes, to better escape predators and to combat parasites.
Reproduction allows organisms to make a new generation of individuals of the same species. (Kratz and Spock, 2024) Gregor Mendel famously studied reproduction in pea plants, and how they can produce a diversity of traits each generation when individuals inherit different combinations of the variation (alleles) in the parent plants. As time goes by, a species can change its traits according to the genes that are combined this way, and depending on which combinations are best suited to overcome environmental challenges. Researchers examine how these changes occur in natural populations over very long periods of time, such as by studying flies, birds, and bats, which have all evolved the ability to fly but independently of each other because theya re not close genetic relatives (yourgenome.org/theme/what-is-evolution/). Co-evolution also occurs frequently in natural populations, where two species or groups of species have evolved alongside each other to change each other’s traits (Yourgenome.org). For example, the shape or smell of a flowering plant species can evolve to attract a specific pollinator species, where bees and certain other animals are great co-evolution examples.
The book Darwin’s Reach: 21st Century Applications of Evolutionary Biology by Norman A. Johnson has a section that explains how evolutionary medicine can help us understand the process by which the traits evolve in organisms like humans, to create certain disease problems. The information from evolutionary biology and how other animals have evolved to overcome disease problems can also help guide our abilities to create medicines useful against a wide variety of health issues, like autoimmunity, antibiotic resistant bacterial pathogens, mismatched-diet diseases, sickle cell disease, and cancer (Natterson-Horowitz, and Bowers, 20212.
Evolutionary medicine is a field study that examines human health and disease using evolutionary principles and the evolutionary history of humans as a species. This field emerged in the early 1900s, especially through the work credited to its founders George Williams, Randolph Nesse, and Stephen Stearns. These scientists looked beyond the role of medicine to treat disease in the present, and instead focused on how human evolution has shaped our vulnerability to health and disease problems. Evolutionary medicine describes how many chronic diseases we have today result from cultural changes that happen much more rapidly than human biology can evolve to keep pace. For example, obesity and Type 2 diabetes are both becoming global epidemics as high-sugar and high-fat foods have become plentiful, replacing healthier foods in our typical diets. Evolutionary medicine looks at how essential nutrients important for our cells are not compatible with processed foods which lack them, and can explain why the function of our genes is not adjusted to modern diets.
Viruses and Bacteria
What are the similarities and differences among viruses and bacteria, which are both important for infectious diseases in humans? Both bacteria and viruses are microscopic, but bacteria are cellular organisms whereas viruses are not made of cells and are generally hundreds of times smaller than bacteria. Bacteria traits are passed across generations through DNA, just like in humans and other large multicellular species. But viruses can have either RNA or DNA, surrounded by a shell made of proteins called a capsid that is a coat-like structure which protects the virus against environmental stressors such as heat (Dr. Sarah Finch’s Youtube).
Viruses cannot multiply on their own like bacteria. Instead, a virus needs to infect a cellular organism host, like a multicellular human or a single-celled bacterium, to make virus copies. The virus takes over the metabolism of a cell, instructing the cell to use energy to make new virus copies that can exit to infect more cells. The rate of the virus reproduction through hijacking the cell can be very fast. In addition, some viruses can live outside of a cell attached on a nonliving object surface for a few days, until a new host is encountered. This type of virus behavior was studied in a meat packaging plant during the COVID-19 pandemic, to help understand why workers were getting sick. I will share that study in the latter part of this section.
It is important for students to learn that not all bacteria are harmful to humans, and many bacteria species are essential for our health, for example. In our seminar with Dr. Paul Turner, we learned that our skin sometimes has bad bacteria, but there are also many good bacteria that help prevent pathogens from entering the human body. The same holds for bacteria within our bodies, such as the gut microbiome that contains species that aid in digesting food and found in the human stomach and intestines. Clearly, we need good bacteria to help us digest and break down our food into useful resources.
Featherstone, A. B., Arnald, J.T.M.M., Brown, A.,& Dass, S. C. (2024) studied how viruses can cling to surfaces which is an adaptation to help infect hosts such as humans at a later time. Viruses can remain on surfaces like stainless steel, PVC, and ceramics for up to five days. Featherstone and colleagues studied this situation in meat packaging plants, to explain how COVID-19 might have changed to different variants by 2020 that better survive on surfaces. Many meat packaging plant workers worked at the plant without knowing that other variants of COVID-19 mutated to live longer on surfaces—which helps explain how the virus continues to spread through an epidemic. The virus had many ways to be transported, like the viruses passing through the HVAC, standing close to other workers, sharing equipment, and sharing living space. The media described how COVID disease was easily spread through droplets (such as in a sneeze), because viruses clinged to the droplets allowing movement between host individuals. It was hard to understand the speed and amount of time the virus stayed alive outside of hosts and traveled between hosts. The virus lived long enough on stainless steel, PVC, and ceramic surfaces for up to 5 days to help its spread. The workers at the plant had to take extra precautions at work once this information became known. Featherstone, A. B., Arnald, J.T.M.M., Brown, A.,& Dass, S. C. (2024)
The Navajo elders and ancestors had a saying for our generation: “Everything is alive; respect nature, acknowledge nature, and all will come back to balance.” The readings and study of evolutionary medicine, such as the book we read by Norman A. Johnson, emphasize that it is useful to understand this balance and to respecting what nature has given. The book describes the problem of widespread antibiotic resistance in bacteria, and how their naturally evolved enemies, phages (bacteria-specific viruses), can be used to combat these infections. This is evolutionary medicine at its finest, working to find a solution to combat the rise of antibiotic resistant bacteria by understanding molecule-level interactions between these microbes. Chan, B.D., M. Sistrom, J.E. Wertz, K.E. Kortright, D. Narayan, and P.E. Turner, 2016. Phage selection restores antibiotic sensitivity in MDR Pseudomonas aeruginosa. Nature Scientific Reports 6:26717 was a study described in Johnson’s book, where scientists used specific phages that attacked antibiotic-resistant bacteria and selected for the bacteria to evolve phage-resistance, making the bacteria less capable of causing disease or switching back to being sensitive to antibiotics. By focusing on evolution in response to the phage, natural selection causes the population of cells to become re-sensitized to antibiotics and, in turn, makes antibiotics work again as we intended.
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