Humans are walking ecosystems and microbes rule their evolution

We might like to think of ourselves as autonomous entities but, in reality, we’re more like walking ecosystems, teeming with bacteria, viruses, and other microbes. It turns out that differences in these microbes might be as crucial to evolution and natural variation as genetic mutations are.

Understanding biological variation

This novel perspective was discussed in a recent publication by Seth Bordenstein, director of Penn State’s One Health Microbiome Center, who is a professor of biology and entomology and holds the Dorothy Foehr Huck and J. Lloyd Huck Endowed Chair in Microbiome Sciences.

Bordenstein, along with 21 colleagues from around the globe, collectively known as the Holobiont Biology Network, propose that understanding the relationships between microbes and their hosts will lead to a more profound understanding of biological variation.

Microbes in the process of evolution

We’ve all heard the term evolution before, but what does it really mean?

“The longstanding definition of evolution is the process by which living things change over time due to gradual mutations and adaptations to their environments,” explains Bordenstein.

These adaptations are commonly driven by natural selection, a process that involves advantageous traits being passed on down the lineage.

However, when we incorporate the microbiome, the collection of all microbes in and on a host organism, the process of evolution becomes a whole lot more interesting and complex.

New paradigm: Holobiont biology

Traditionally, we’ve kept the visible and invisible forms of life separate in the way we consider and study them. Many scientists still think of microbes in terms of background noise or minor contaminants.

But it turns out that this approach may have been selling the microbes short.

“Microbes are the base of the biosphere,” says Bordenstein. “Every host organism lives in contact and association with microbes, and those microbes can cause variation in traits.”

This realization has given birth to a new concept – holobiont biology; a multidisciplinary and holistic understanding of how life’s forms and functions depend upon relationships between microorganisms and their hosts.

Holobiont biology considers organisms and the microbes with which they are inseparably linked as a whole, rather than as separate entities.

Harnessing the power of the microbiome

The field of biology traditionally categorizes living things into taxa. But holobiont biology poses a challenging and exciting opportunity to rethink this framework.

“We’re making the case that organisms are not autonomous. They exist, by definition, always in association and in contact with microbes,” explains Bordenstein.

This novel way of thinking could open doors to harness the power of the microbiome to improve health, resilience in environmental sustainability, and advancements in agriculture.

Think of it: what if we could use microbes to combat chronic diseases like cancer or make agriculture more resistant to climate change?

Revisiting microbes and evolution

Darwin’s famous treatise, Origin of Species, is a cornerstone of modern biology. However, it was written with species of animals and plants in mind and did not consider the multitude of invisible microbes that are part of every individual macro-organism.

Now that we know so much more about the fundamental role of microbes in the biosphere, we can add a new layer to our understanding of evolution.

Genetic diversity and evolution

In the 1920s to 1940s, biology witnessed a revolution known as the Modern Synthesis, where Mendel’s genetic laws were merged with Darwin’s theory of evolution. This created a comprehensive explanation for how new variations of form and function develop over time.

We may well currently be at the cusp of another revolution, a post-Modern Synthesis. As Bordenstein points out, we’re now factoring in the role of microbes in our understanding of genetics and evolution.

Shifting paradigms in life sciences

How do we incorporate this new understanding of the importance of microbes in the biology and evolution of all organisms? The Holobiont Biology Network authors state that this needs to start with redefining and re-teaching biology.

“We’re thinking of animals and plants as a consortium of host and microbial cells that influence anatomy and physiology,” explains Bordenstein.

There’s also a need for new analytic tools to determine the contribution of microbes and how they interact with genetics to explain traits. Once we have these analytic tools in place, we can engineer microbes and microbiomes as much as we can engineer genes to yield better outcomes for organisms.

Microbes shaping our evolution

Microbes have been here for four billion years, and they outnumber the stars in the universe by orders of magnitude. There are more bacteria in your mouth than there are people on the planet. They have shaped our world in ways we are only just beginning to understand.

Research shows that they may also play a role in determining who is more likely to develop colon cancer, have high cholesterol levels or an average body mass index. After all, we contain not only our own genes, but also those of the billions of micro-organisms that live in and on us.  

“What we’re learning today and over the past decade, is that sometimes microbes explain more biological trait variation in organisms than the genes do,” Bordenstein says.

The future of biology lies not just in our genes, but in the characteristics of our associated microbes too. As we move forward, remember this: we’re not lone entities. We’re ecosystems.

The study is published in the journal Science.

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