Evolvability: The race against extinction

By Bryan Moyers

It’s easy to think that evolution only works over long periods of time.  As much as 4.1 billion years ago, life began on Earth.  Some 420 million years ago, animals found their way onto land. Around 65 million years ago, an asteroid wiped out most dinosaurs. Two million years ago, our genus, Homo, emerged.  It almost seems like evolution is a strictly theoretical field.  After all, evolution doesn’t affect things in our lifetime…  right?

In fact, evolution can happen rapidly.  The Peppered Moth population drastically changed color over 47 years in 19^th-century England in response to industrial soot.  Nylon, first created in 1938, was being eaten by bacteria by 1984, thanks to gene duplications.  Other times, species don’t evolve quickly enough.  In about 50 years, reindeer on St. Matthew’s Island wiped out their food supply and didn’t adapt to a new food source.  If a species can’t evolve on a short timeline, the punishment can be extinction.  But what determines if species will evolve or not?  Evolvability. Evolvability is an important concept in evolution which guides both how we conduct research and helps us solve problems for the future, but it’s not often talked about.

All species have some ability to adapt to their environment—after all, that’s the only way they’ve survived as the world has changed.  How well a species evolves in its environment is called evolvability.  If evolution is a race, evolvability is how fast each species can run and which routes it can take.  No species is really racing against any other species in particular. Instead, they’re all racing away from an avalanche called extinction.  Each species is running as fast as it can, finding shortcuts to escape, and leaping on or over each other in a chaotic horde. What makes a species faster and more mobile than another in the eternal and brutal race of evolution?

External factors in evolvability

Before a species can adapt to a new environment, it must first be able to survive in that environment. In the race against extinction, some hurdles are just too large to jump. For example, if all human food sources were suddenly wiped out, we likely wouldn’t be able to evolve, since we would quickly starve. Instead, if most of our food sources were depleted we could live off of a less hearty but still nourishing food, perhaps some kind soup featuring insects (and that’s a real possibility). Over time, humans might evolve to get enough nutrition from our food sources. Adaptation to food sources has been a theme in human evolution, such as farming populations losing their adult lactose intolerance several thousand years ago.

Surviving in a new environment isn’t just about food. “Environment” refers to many things, including other species. If an environment is too cold, humans won’t survive there for long. On a planet whose surface is composed entirely of rabid wolves, humans are goners.

Of course, different species can survive in different environments. Some species are completely at home on volcanic vents, others on frigid mountaintops. In the race against extinction, different roads are open to different species.

Species evolvability

How a species evolves and thrives depends on the species. The first thing any population needs for evolution is genetic variation. If all members of a population have identical genomes, then who lives or dies doesn’t matter to future generations. Genetic variation can arise in many ways, all of which can be called “mutations”. While we often associate the word “mutation” with harmful changes, most mutations are “nearly neutral”, meaning that in most situations they’re neither good nor bad. And whether a mutation is “good” or “bad” depends on the environment. One well-studied example is the sickle cell anemia mutation. It is beneficial for some people living in areas where malaria is prevalent, but overall more harmful where the disease isn’t common. But a species that accrues too many mutations too quickly is likely to lose beneficial traits. In the analogy of evolution as a race, a species can run both too slow or too fast, tripping over obstacles and perhaps missing important shortcuts.

Another major factor in evolvability is the number of individuals in a species. A large population size creates more opportunity for genetic variability, which means that when things get tough, it’s more likely for at least some members of the population to survive.   Those survivors will then reproduce, leading to future generations with the genetic differences that increase survival.  So large populations are more evolvable because they have more material to work with—while escaping the extinction avalanche, they can see more paths and follow the safest.

Other factors are thought to influence species’ ability to evolve, but are more difficult to quantify.  For instance, species that reproduce sexually are more evolvable than comparable species that reproduce asexually.  Sexual recombination allows the next generation to sample more combinations of genes.  Also, sexual selection (such as when female deer are more attracted to males with particularly large antlers) seems to make genes governing those traits much more variable.

Co-evolving with another species (such as an evolutionary arms race) makes a species more evolvable.  Because this is a relationship between species, how one species evolves changes the way the other evolves.  So, whether it’s the coevolution of phages and their bacterial hosts or symbiosis between fungi and plants, the genes are evolving in complicated and interdependent ways.  Such co-evolution seems to increase the complexity of a system.  The “complexity” of a system is hard to define, but in this case part of the definition is more genetic information. (Aside: It’s difficult to support this claim, since few or no species exist in a vacuum for comparison.  This finding was based on a computer simulation.)  With more genetic information available, there is greater chance for variation (and thus evolvability).  Aside from complexity, genetic information seems to be more variable during co-evolution.

In fact, so many traits seem to influence evolvability that some experts think evolvability itself might be a selectable trait.  If that’s true, then the more evolvable a species is, the more it will out-race less evolvable organisms.  While there are surely limits, this would imply a positive feedback loop where the evolutionarily rich get richer.

The importance of evolvability

Theodosius Dobzhansky said, “Nothing in biology makes sense except in light of evolution.”  Evolvability guides our decisions about laboratory studies.  Species with large populations, such as bacteria and yeast, allow us to approach questions about evolution more easily because of the relationship between evolvability and population size.  Evolvability also helps us address pressing challenges.  Understanding how well pathogens evolve to our medical treatments has implications for public health, so the concept of evolvability is being used in an attempt to predict future pathogens.  Our rapid alteration of the Earth’s climate puts huge numbers of species at risk, and understanding the dynamics of evolution may help us mitigate our damage and map out the road to recovery.

Evolvability is hugely important, but it is only one small portion of evolution.  There are major, compelling questions about the origins of life and our species.  As we see the number of species dwindling, we wonder about the causes of extinction and how quickly our planet can recover.  With the incredible rise of human technologies, we can ask how we’re inadvertently changing the directions in which our species—and other species—are evolving.  The study of evolution isn’t just about stuff that happened a long time ago, but it helps us answer questions that are important to us right now and tackle problems that are likely to face us in the future.  In the meantime, keep racing!

About the author

 

Our second co-founder, Logistics Coordinator, and Senior Editor, Bryan Moyers, is a doctoral student in the Bioinformatics program at the University of Michigan. Bryan’s research focuses on methodological problems in molecular evolution, and correctly inferring information from data. In other words, his research sheds light on problems with the methods commonly used in the field of Evolutionary Biology so that improvements can be made. Bryan holds degrees in Biology and Psychology from Purdue University. His interests are in science and education issues, philosophy of science, and the intersection of science and business. Outside of science, Bryan enjoys reading, running, hiking, and brewing/consuming beer.

Read more from Bryan here.