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Evolution stands as one of the most significant breakthroughs in science. With a deep understanding of the interconnections between all forms of life on Earth, biologists have uncovered a wealth of remarkable findings. The evidence supporting evolution is so overwhelming that questioning it is as senseless as denying the existence of the moon. Yet, there are still those who challenge the occurrence of evolution. Speciation, the process where a new species arises from a common ancestor, unfolds over extended periods, but key evolutionary steps are observable. Below are eight noteworthy examples of evolution in action.
8. The Peppered Moth
Let’s begin with a well-known example of evolution, often featured in textbooks. Initially, most peppered moths (Biston betularia) displayed a light, speckled pattern, which helped them blend in with their surroundings and avoid predators. Before the Industrial Revolution, a dark variant of the peppered moth made up only 2% of the population. However, following the Industrial Revolution, this dark variant surged to represent 95% of the population. The most accepted explanation for this shift is that the light-colored moths lost their camouflage advantage as industrial pollution darkened tree trunks, making them more visible to predators. Although the peppered moth example has faced some criticism, particularly regarding the cause of the color shift, it remains a strong illustration of evolutionary change through mutation, variation, and natural selection.
7. Live Birth in Three-toed Skinks
The example of the peppered moth is often used in textbooks because it demonstrates evolution through a single trait. However, speciation involves multiple mutations leading to substantial transformations. The yellow-bellied three-toed skink (Saiphos equalis) is a lizard found in New South Wales, Australia, and it appears to be transitioning from egg-laying to live birth. This species is unique because it can either lay eggs or give birth to live young, offering scientists the opportunity to observe the adaptations necessary for live birth. Skink embryos inside eggs receive additional calcium, which live-born skinks do not. To compensate, the mother secretes extra calcium to nourish her developing young, which seems to be an early step toward evolving a mammalian-like placenta. Coastal skinks typically lay eggs, likely due to stable warm temperatures that are ideal for embryo development. In contrast, skinks living in the cooler mountains tend to give birth to live offspring, with the mother's body providing a more consistent temperature. It is likely that over time, these two populations will evolve into distinct species, each adapted to its specific reproductive strategy.
This raises a familiar question from Creationists—If humans evolved from apes, why are there still apes? The situation with the skinks provides a clear answer. If one population of skinks evolves from egg layers to live-birthing forms, why would egg-laying skinks still exist? Because each reproductive strategy is perfectly suited to its respective environment.
6. The Arms Race between Crabs and Mussels
Evolution often occurs simultaneously; as predators evolve new methods for hunting, prey species that develop mutations improving their chances of survival are naturally selected, leading to shifts in the prey population. We don’t always have to wait for a predator’s evolution to observe this process. In modern times, human activity—particularly the movement of species across the globe—has made it possible to witness new interactions between species. A notable example is the Asian shore crab (Hemigrapsus sanguineus), an invasive species in New England that preys on native blue mussels. Recently, it was observed that when mussels detect these crabs, they respond by thickening their shells to prevent being eaten. However, this adaptation comes at a cost to the mussels, making it a highly regulated response. The evolutionary aspect here is that only mussels from areas where Asian shore crabs are native show this shell thickening behavior, while those from regions without crabs do not see them as a threat. This is an early stage in what could become an evolutionary arms race.
5. Italian Wall Lizards
In 1971, ten Italian wall lizards (Podarcis sicula) were introduced to the island of Pod Mrčaru from a nearby island. After being left undisturbed for several decades, these lizards were studied and compared to their original population. The wall lizards on Pod Mrčaru, having passed through a genetic bottleneck, adapted remarkably well to their new environment. Notably, they shifted from an insect-heavy diet to one predominantly consisting of vegetation. This dietary change seems to have prompted significant physical adaptations in the lizards. The lizards on Pod Mrčaru now have larger heads and much stronger bite forces, which are essential for consuming plant matter. The most exciting evolutionary development, however, is the appearance of cecal valves—muscles that partition the intestine, slowing food passage so that gut bacteria can break down plant material for nutrient absorption. This is a completely new feature in the Italian wall lizard and a major evolutionary milestone.
4. Mexican Cavefish
The Astyanax mexicanus, also known as the Mexican cavefish or Mexican tetra, has lost its eyes over time. While this may seem like a loss, it’s actually a form of evolutionary adaptation, one that leans toward de-evolution. The cavefish originally had eyes, but the energy required to use them became unnecessary due to the scarcity of food in caves. Researchers explain, “Any animal that lives in permanent darkness and doesn’t need its vision to find food or avoid predators won’t really need its eyes or visual centers in the brain.” These fish, which are omnivores, have adapted by eating almost anything available, including scavenging dead animals and plants. In addition to losing their vision, cavefish have also lost the camouflage coloration seen in their surface-dwelling relatives. This is an example of regressive evolution, which follows the principle: “if you don’t use it, you lose it” when it comes to certain traits.
3. Evolution in the Lab
The rise of drug-resistant pathogens has shown us that evolution can be most easily observed in species with rapid generational turnover. Since 1988, Richard Lenski’s lab has been studying the evolution of twelve E. coli populations, all descending from a single ancestral strain. Over 50,000 generations of E. coli have been observed, and the differences between these populations and their ancestor strain have been carefully documented. Regular samples have allowed researchers to track the genetic changes over time. As a result, the bacteria have become significantly more efficient at growing under the lab conditions provided. This ongoing study has given us a unique look at how evolution unfolds. One population of E. coli even evolved the ability to utilize citrate as a nutrient—something not typically observed in E. coli under similar conditions. “Life Evolves!” This quote comes from a remarkable letter Lenski wrote in response to a particularly obnoxious creationist. The full series of letters can be found here.
2. Butterflies and Parasites
Studying evolution often takes a long time, but sometimes change can occur in the blink of an eye. The Blue Moon Butterfly (Hypolimnas bolina) of the Samoan islands faced a devastating parasite that targeted male embryos, resulting in a severe gender imbalance where males made up only 1% of the population. Remarkably, within just ten generations (~1 year), the male population surged to 40%. This change didn’t occur because the parasite disappeared—it's still present—but now it no longer kills male embryos. This example demonstrates how a beneficial mutation can spread rapidly throughout a population. Any male that developed immunity to the parasite would have the opportunity to mate with many females, spreading his immunity through the gene pool.
1. Darwin’s Finches
This isn’t just a simple retelling of Darwin’s initial observations of adaptation among the finches of the Galapagos. These finches continue to play a crucial role in our understanding of evolution. Peter and Rosemary Grant spent years studying the finches on one of the Galapagos Islands and observed firsthand how evolution is driven by the direct competition between two rival species. The medium ground finch, which had been well-established on Daphne Island, was perfectly adapted to cracking large nuts with its beak. However, in 1982, the large ground finch from a nearby island arrived and began to outcompete the native medium ground finches, driving them away and consuming all the large nuts. Over the course of their study, the medium ground finches on Daphne Island evolved to have smaller beaks, better suited to eating the smaller nuts that the larger finches ignored. This is a quintessential example of evolutionary biology in action.
