Evolution Part One: Natural Selection and Extinction

Natural selection explains how environmental conditions affect which heritable traits become more common in a population. Extinction concerns the disappearance of a species. Together, they help us examine how an advantage depends on the conditions in which it works.

One shorthand is “adapt or die.” It captures the pressure of environmental change, but it can suggest that organisms choose how to evolve. Selection operates through differences in survival and reproduction among organisms with varying traits.

The word selection can be confusing because it usually implies a choice. In biology, it refers to differences in reproductive success associated with heritable variation. Biologist Geerat J. Vermeij describes it as “nonrandom elimination.”

Charles Darwin spent decades studying the natural world. His account of natural selection explains how traits affecting survival and reproduction can change in frequency over generations. The advantage is relative to the environment; a trait useful under one set of conditions may become costly under another.

Natural selection “is very much about advantages in the here and now, not in the distant future. Traits conferring long-term advantages emerge because they also work well in the lives of individuals and produce positive feedbacks.” [1] Selection does not anticipate future needs. A mutation’s effect depends on its consequences for reproduction in the conditions organisms encounter. Some variants are neutral, and survival is only part of reproductive success.

Consider zebra speed as a simplified example. If faster zebras are more likely to escape predators, reproduce, and pass on the relevant traits, those traits can become more common. Speed is only one influence: eyesight, strength, disease, and other conditions can also matter. As Rafe Sagarin notes in Learning from the Octopus, “Natural selection … is an incredibly simple process requiring just three simple elements—variation between individuals, environmental conditions that favor or select certain variants over others, and a means to reproduce those variants that are better suited to the environment.” [2]

Organisms in nature have survived and thrived for billions of years because they have one powerful trait at their disposal—they are adaptive.

Rafe Sagarin [3]

Variation need not disappear as selection operates. Different traits can provide advantages, and their effects depend on trade-offs and circumstances. For biological evolution by natural selection, the relevant variation must be heritable. Learning and cultural transmission can also spread behaviors, but they should be distinguished from genetic inheritance.

New circumstances tend to be calamitous for an economic unit if they are either very large or very rare relative to the size and lifespan of that unit.

Geerat Vermeij [4]

Natural selection does not require organisms to act for the survival of their species. Nor does every feature have to be an adaptation. Changes that affect the success of individuals can have consequences for populations and ecosystems that extend beyond the advantage to those individuals.

Most species that have existed are now extinct. Extinction occurs when the last member dies: the last passenger pigeon, Martha, died in captivity in 1914. A population can lose its practical prospect of recovery earlier. At low population density, difficulty finding mates or other effects can reduce its growth rate; these are Allee effects. [5] A species can also be extinct in the wild while individuals remain in captivity. Passenger pigeons illustrate how human activity can drive a once-abundant species to extinction.

An extinction can have several interacting causes, and evidence for their relative importance may be incomplete. Some disappearances are rapid; others unfold over long periods. Competition, habitat loss, climate change, introduced species, and disruptive events can all contribute.

Species competing for the same limiting resources may be unable to coexist indefinitely under stable conditions. An introduced competitor can therefore threaten a native species. Changes in the environment can also remove resources or alter conditions faster than a population can respond.

Ecosystems contain complex interdependencies. Losing a prey species can threaten a predator that has no alternative food. Losing a predator can allow its prey to increase and put pressure on other species. These relationships make the consequences of an extinction difficult to predict completely.

Counting extinctions also depends on identifying distinct species, which can be difficult. Many species have disappeared without ever being catalogued. The estimate cited in the source is 10 million distinct species, with fewer than 20% [6] catalogued. [7]

Specialization can be valuable in stable conditions and costly when those conditions change. Generalists may have more alternatives when a food source or habitat is lost, but the advantage depends on the disruption. Rats, cockroaches, and pandas illustrate different ecological requirements; they do not establish that every generalist will outlast every specialist.

Reproduction rate also affects recovery. A population that can increase quickly may recover more readily from a decline, provided resources and other conditions permit. Slowly reproducing species may take longer to recover.

Large population losses can occur without extinction. Deer and elk, for example, can exceed the food available in an area and suffer starvation. Reduced numbers may ease pressure on resources, but this does not mean mass starvation is necessary for a species to survive. [8]

Background extinctions occur over time from varied causes. A mass extinction involves a large loss of species over a geologically short period. Major disruptions, such as the effects of an asteroid impact or severe environmental change, can affect many species together.

As a business analogy, these ideas invite questions about dependence on current conditions, specialization, and the ability to respond to change. A business can deliberately change its practices; biological evolution does not plan ahead. The analogy is useful when those differences remain clear.

So how does a business survive in constantly changing environments? When change hits, a common response is denial or trying to adapt with a business model that no longer works. We can influence the outcome in changing environments more rapidly by first recognizing that we actually need to survive and then moving to survive with new ideas.

Roberta Bondar [9]