March 20, 2023
The study of evolution is breaking, and that can be a good thing

The study of evolution is breaking, and that can be a good thing

Credit: Darkdiamond67/Shutterstock

How will life on Earth and the ecosystems that support it adapt to climate change? Which species will disappear—or evolve into something new? How will microbes develop further resistance to antibiotics?

These kinds of questions, which are of fundamental importance to our way of life, are all at the heart of evolutionary researchers and will prove increasingly important as the planet warms.

But finding the answers is not the only challenge facing evolutionary biology. Charles Darwin’s theories may be over 150 years old, but the big questions about how evolution works have not been settled.

Evolutionary biology is now in one of the most intense debates it has had in more than a generation. And how this debate plays out could have a major impact on the future of this scientific field.

Some biologists and philosophers argue that evolutionary biology needs reform, arguing that traditional explanations of how organisms change over time, as scientists have assumed since the 1930s, prevent the assimilation of new findings

Modern evolutionary biology, a vocal minority argues, is incomplete. The dominant and traditional view of the field is very concerned with how genes in a population change over time. This neglects, these critics argue, how individual organisms shape their environment and adapt over the course of their lives to survive and reproduce.

Some go so far as to say that evolutionary theory itself is in crisis and must be replaced with something new.

Not all biologists are convinced. Some argue that repeated calls for reform are misguided and can actually hinder progress.

Modern evolutionary theory

The version of evolutionary biology that is still largely taught in schools has its origins in modern synthesis. This combined Gregor Mendel’s theory that organisms inherit distinct particles (what we now call genes) with Charles Darwin’s theory of natural selection. Darwin proposed that environmental conditions eliminate heritable traits that are not useful and promote those that give organisms an advantage.

The modern synthesis aimed to unify biology, but was dominated by a few subfields, particularly genetics and paleontology, and focused on how populations change their genetic makeup over time. In this view, organisms are objects and the raw material for natural selection.

Notably, the modern synthesis did not incorporate all fields. The study of how embryos develop and how organisms interact with each other and their environment (ecology) was largely omitted.

Organisms are not, critics of modern synthesis argue, passive objects of natural selection. Instead, they say, organizations are agents that change these environments.

A famous example is the beaver, which builds dams to survive and reproduce, changing its environment in the process. This distortion in turn affects natural selection on itself and other species, thereby altering the beaver’s long-term evolution.

Organisms also inherit more than DNA. This challenges the assumption of modern synthesis that traits acquired by an organism during a single lifetime cannot be passed on.

There is cultural transmission: killer whales teach their children and grandchildren hunting skills and food preferences. Songbirds transfer nutrients to new generations in eggs, just as humans give their offspring antibodies through breast milk. Some biologists say these gifts can revitalize the study of evolutionary biology, distracting us from strict genetic inheritance.

Diversity is strength

As an evolutionary ecologist with an interest in how organisms adapt to their environment, I am not as concerned as some that the current version of evolutionary biology is incomplete. Nor am I particularly concerned about the limitations of population genetics.

The study of evolution is breaking — and that can be a good thing

The transmission of information between generations can affect the evolution of a species. Credit: Monika Wieland Shields/Shutterstock

Evolution can clearly be described as a change in gene frequency between generations. But this does not mean that population genetics is the only useful way to study evolution.

Biologists may disagree about what constitutes an evolutionary process, with natural selection and random changes in DNA being the two best-studied processes. However, evolutionary processes are not the only interesting aspect of evolution.

Evolutionary outcomes and products of evolution—organisms and how they develop—also keep biologists busy. We understood more about how genes and environments interact to shape the development of organisms. These insights from evolutionary developmental biology have clearly enriched our field.

That evolutionary biology is increasingly falling apart does not worry me either, as long as we recognize that a plurality of approaches is not a weakness, but a strength. If physicists can’t agree on a grand unified theory of the universe, why expect biologists to agree on one beyond what we’ve already achieved? After all, organisms are much more complex than physical particles and processes.

To take another example from physics, light can be thought of as either a particle or a wave. This duality reflects how a single descriptor is not sufficient to fully describe the complex phenomenon of light.

If this works for physicists, why couldn’t evolutionary biologists also use multiple ways to study a process as complex as evolution and things as complex as organisms? Why can’t we see organisms either as agents capable of modifying their environment or as objects subject to natural selection, depending on the context? These are two valuable and complementary perspectives.

Evolutionary biology today is a messy patchwork of many loosely connected subfields. This reflects the vast variety of phenomena we study and the many interests of biologists.

We are united in accepting that natural selection based on heredity and random factors have jointly shaped organisms — but not much more. Maintaining a coherent overview, either of the modern synthesis or some extension of it, seems increasingly hopeless.

Abandoning the search for a grand unifying theory of evolution will not harm our field, but rather set us free. It will allow biologists to think more freely about the endless forms of beauty that are constantly evolving and will continue to do so.

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