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Vet Advice: Evolution gone wrong

Vet Advice with Dr. Ron Clarke

Vet Advice: Evolution gone wrong

Alex Bezzerides, a Lewis-Clark State College biology professor, describes the imperfect system that is the human body in his new book, Evolution Gone Wrong: The Curious Reasons Why Our Bodies Work (Or Don’t). It is a humorous examination of why we are what we are. In the author’s words, “I just didn’t realize how many things humans are up against.” He links much of human fallibility to chance miscues in the evolutionary chain of events over thousands of years.

Does the same hold true for domestic animals, their diseases and much shorter periods of evolution under the grip of human control?

Stephen Hawking opened one of his many academic lectures with the question: “Does our Creator play dice?” In answer to his own question: Not only does God play dice, but does so by throwing them where they can’t be seen.

According to Bezzerides, our existence on this planet is the product of chance, timing and a whole lot of evolutionary compromise. Our ability to speak and walk upright and gestate babies with big brains has meant sacrifice and discomfort. The human condition we’ve created for ourselves is eternally humbling and peculiar. Bezzerides considers the hyper-aggressive human fetus as invasive, an explanation for the degree of placentation in humans that far exceeds the degree of placentation in other mammals, starting with the concept that menstruation evolved in women in response to building the uterine lining in preparation for pregnancy. This is a big difference from many mammals that remodel the uterine lining in response to pregnancy.

The question Bezzerides leaves with readers: “How does anybody have kids? After seeing the whole thing, you feel like there should be like 40 people on earth rather than seven billion.”

When you talk about bipedalism and people standing on two feet over millions of years, many things changed about the shape and nature of the body. It made life difficult for our ankles, our feet, our arches and our knees, but the evolution of hands proved to be a remarkable evolutionary event.

Infectious pathogens are arguably among the strongest selective forces that act on human populations. They became the real predators of the 21st century. On the human side, HIV, influenza and COVID-19 killed millions across the globe. Migrations and cultural changes during recent human evolutionary history (the past 100,000 years or so) exposed populations to dangerous pathogens as people colonized new environments, increased in numbers and had closer contact with zoonotic disease vectors. This includes both domesticated animals such as dogs, cattle, sheep, pigs and fowl; and animals exploiting permanent human settlement such as rodents, bats and sparrows.

Host genetics strongly influence an individual’s susceptibility to infectious disease. Pathogens that diminish reproductive potential, either through death or poor health, drive selection of genetic variants that ultimately affect resistance. Selection is likely to be most evident for pathogens with a long-standing relationship with Homo sapiens, diseases such as malaria, smallpox, cholera, tuberculosis and leprosy. New diseases such as HIV, COVID-19 and Ebola were introduced very recently in the evolution narrative and where the endpoint exists is still a big question.

On the animal side, we contend with new threats such as coronavirus, highly pathogenic swine diseases that come in unpredictable waves and viral diseases that “fall from the trees” as plantations replace old-growth forests. Some pathogens cause acute illness and death, yet once survived, pose little additional threat. Other pathogens produce chronic infections that impair nutritional well-being, growth and fertility. Timing, strength and dynamics of disease shape the patterns of change. Some permanently alter animal genomes. The “signatures of selection” will vary with animal age, geography and pathogen virulence.

The cattle feeding industry started in the 1950s and 1960s and represents a dot in the evolutionary scale of the beef industry. As a result, and despite much research, respiratory disease, gastrointestinal disturbances, liver abscesses and injury from horns remain common production barriers. The cascade of disease following calves from pasture to feedlot to slaughter has not significantly decreased. Despite new antimicrobials, antiparasiticides and growth promotants, many feedlot owners claim overall mortalities have changed very little. Disease patterns have changed significantly, treatment protocols remain elusive, names of diseases are continually added to the feedlot jargon and costs go up.

Seventy per cent of diseases that have emerged in humans in recent decades are of animal origin. Will evolution change those numbers?

Farming and the veterinary profession are changing. There are reports of a recruitment and retention crisis for farm animal veterinarians. This is a worldwide concern with no easy solutions. Efforts targeted at the key stages of the pipeline might help. The profession is keying on the following to find answers:

  • Outreach from and admissions to veterinary schools.
  • Training and inspiring veterinary students at veterinary school.
  • Recruiting and retaining vets into jobs in farm animal practice.
  • Ensuring farmers receive the services they need from sustainable veterinary businesses.

The veterinary profession, and agriculture, must work to be more inclusive. Many people are put off a farm veterinary career because they think that they must be from a farming background. Discrimination and harassment working on farms also deter many veterinary students and qualified veterinarians from the farm sector. The veterinary profession and farmers stand to benefit from better diversity if this is improved. (See Ensuring the veterinary profession meets the needs of livestock agriculture now and in the future by John Remnant, a Nuffield Farming Scholarship Trust Report).

We must keep in mind that the future of the universe is not completely determined by the laws of science, and its present state, as Hawking thought. The Creator still has a few tricks up its sleeve. As such, ostriches have survived and evolved with one of the strongest immune systems in the animal kingdom. They can live up to 65 years in harsh environments and withstand viruses and infections that most animals cannot.

Evolution has a place.

About the author


Dr. Ron Clarke

Dr. Ron Clarke prepares this column on behalf of the Western Canadian Association of Bovine Practitioners. Suggestions for future articles can be sent to Canadian Cattlemen ([email protected]) or WCABP ([email protected]).



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