Charles Darwin was a creationist and a trained naturalist and geologist. During an ocean voyage in the 1830s, Darwin’s observations of animal and plant life among the Galapagos Islands led him to develop his theory of evolution. He held onto the idea for 20 years without publishing it, until Alfred Russel Wallace, who had come up with the same ideas independently, convinced him to share it with the world.
They presented their findings to the scientific community together, but Darwin’s book on the subject sold much better. He is remembered far better to this day, while Wallace has mostly been forgotten by the general public.
Charles Darwin and Alfred Russel Wallace introduced to the world their theories on evolution in the mid-1800s. Natural selection is the primary mechanism that drives evolution, and evolution can be divided into two subtypes:
These two types are different ends of the same spectrum. They both describe the constant genetic change happening in living species in response to the environment but in vastly different ways.
Macroevolution concerns itself with large population changes over very long periods of time, such as a species branching off into two separate species. Microevolution refers to a small scale evolutionary process by which the gene pool of a population is changed over a short period, usually as a result of natural selection.
Definition of Evolution
Evolution is the gradual change of a species over a long period of time. Darwin himself did not use the term evolution but instead used the phrase “descent with modification” in his 1859 book that introduced the world to the concept of evolution, “On the Origin of Species by Means of Natural Selection.”
Natural selection acts on a whole population of a species at once and takes many generations, over many thousands or millions of years.
The idea was that some gene mutations are favored by a species' environment; in other words, they help offspring possessing it to do a better job of surviving and reproducing. These get passed on at an increasing frequency until the offspring with the mutated gene are no longer the same species as the original individual with the mutation.
Microevolution vs. Macroevolution Processes
Microevolution and macroevolution are both forms of evolution. They both are driven by the same mechanisms. In addition to natural selection, these mechanisms include:
Microevolution refers to evolutionary changes within a species (or a single population of a species) over a relatively short period of time. The changes often only affect a single trait in the population, or a small group of genes.
Macroevolution takes place over very long periods of time, over many generations. Macroevolution refers to the diverging of a species into two species or the formation of new taxonomical classification groups.
Mutations Creating New Genes
Microevolution happens when a change happens to a gene or genes that control a single trait in an individual organism. That change is typically a mutation, meaning that it is a random change that happens for no particular reason. The mutation does not provide any advantage until it is passed on to the offspring.
When that mutation does give the offspring an advantage in life, the result is that the offspring are better able to bear healthy offspring. Those offspring in the next generation who inherit the gene mutation will also have the advantage and will be more likely to have healthy offspring, and the pattern will continue.
Natural vs. Artificial Selection
Artificial selection has markedly similar outcomes on a species population to natural selection. In fact, Darwin was familiar with the use of artificial selection in agriculture and other industries, and this mechanism inspired his conception of an analogous process happening in nature.
Both processes involve the shaping of a species’ genome through external forces. Where natural selection’s influence is the natural environment and shapes traits that are best adapted to survive and successfully reproduce, artificial selection is evolution influenced by humans on plants, animals and other organisms.
Humans have used artificial selection for millennia in order to domesticate various animal species, beginning with the wolf (which, once domesticated, branched off into the dog, a separate species) and continuing with beasts of burden and other livestock that can be used for transportation or food.
Humans bred only the animals who possessed the traits most desirable for their purpose and repeated this each generation. This was continued until, for example, their horses were docile and strong, and their dogs were friendly, adept hunting partners and alerted the humans to coming threats.
Humans have also used artificial selection on plants, cross-breeding plants until they were hardier, had better yields and held other desirable characteristics that might not align with the ones the natural environment would have gradually led the plants toward. Artificial selection tends to happen much more quickly than natural selection, although this is not always the case.
Genetic Drift and Gene Flow
In a small population, especially one in an inaccessible geographical area such as an island or a valley, this advantageous mutation can have an effect relatively quickly on the species’ population. Soon, the offspring with the advantage will be the majority of the population. These microevolutionary changes are called genetic drift.
When a population with a small number of individuals becomes exposed to new individuals who bring new alleles (novel mutations) to the gene pool, the relatively rapid change to the population is called gene flow. By increasing the genetic diversity of the population, the species may become less likely to split off into two new species.
Some Microevolution Examples
An example of microevolution would be any trait that gets introduced to a small population over a relatively short period, through random genetic drift or the introduction of new individuals with novel genetic makeup to the population.
For example, there might be an allele that provides a certain species of bird with a change to its eyes that allows it to have better long-distance visual acuity than its peers. All birds who inherit this allele are able to spot worms, berries and other food sources from farther away and from greater heights than the other birds.
They are better nourished and able to leave the nest to hunt and forage for brief periods of time before returning to safety from predators. They survive to reproduce more often than the other birds; the allele frequency grows in the population, leading to more birds of that species with sharp long-distance vision.
Another example is bacterial antibiotic resistance. The antibiotic kills off all of the bacterial cells except for the ones that are unresponsive to its effects. If the bacterium’s immunity was a heritable trait, then the result of the antibiotic treatment was that the immunity got passed on to the next generation of bacterial cells, and they too will be resistant to the antibiotic.
- Bates College: Microevolution & Hardy-Weinberg Equilibrium
- Stanford Encyclopedia of Philosophy: Evolution
- University of Utah Genetic Science Learning Center: Conservation Genetics
- University of Maryland: Geology 102 - Evolution
- University of California Berkeley: Mechanisms of microevolution
- California State University, Sacramento: BIOL 300 – Foundations of Biology, Telleen - Evolution and Natural Selection