We often think of evolution as an imperceptible, gradual change over time. But consider animals that have evolved right before our eyes: bugs, fish, birds and more. The degree and speed of change varies, depending on environmental conditions and the amount of time between generations. Some species evolved rapidly to adapt to major changes in their environment.

Back in the 1850s, Darwin had assumed that evolution was a slow, invisible process that could take as many as thousands of generations to produce a new species. However, Discover Magazine reported that in 1981 a researcher named David Reznick demonstrated that you can see animals evolve within a lifetime. This was a pivotal moment in changing the way scientists understand evolutionary biology. It turns out that some animals evolve so quickly that researchers can actually observe the changes.

Resznick wanted to watch evolution happen in real time, so he experimented with changing the predators in guppies environment. He moved one group of guppies to a stream without predators to see if they would thrive, and added predatory fish called cichlids to guppy sites that previously didnt have predators.

In just four years, or six to eight guppy generations, the guppies adapted to their new environments. The group in the stream without predators were larger, matured later and reproduced slower. The guppies who lived with cichlids matured at an earlier age and produced more babies.

When brown anole lizards invaded green anole territory in Florida, the green lizards adapted in just 15 years. Discover Magazine reported that only 20 generations after the invasive brown lizards arrived, the green lizards developed larger toepads and more scales, which helped them cling to higher branches to avoid competition from the brown lizards on lower branches.

Salmon have remained resilient, despite several challenges caused by humans. When commercial fishing in the 1920s threatened Chinook salmon from Alaska to California, the fish became smaller and shorter-lived, according to Discover Magazine. Pink salmon have adapted to migrate earlier because of climate change. Salmon are migrating from the ocean to the river two weeks earlier than they did 40 years ago, in response to warmer ocean temperatures. Furthermore, Mental Floss pointed out that this isnt just a behavior change, but a change at the genetic level, with natural selection favoring fish that migrate earlier.

One of the peskiest animals that have evolved quickly is pesticide-resistant bugs. Bedbugs were common in the 1940s and 1950s, according to the BBC, but when humans introduced DDT and other insecticides to control the bugs, the plan totally backfired. By the 1960s, future generations of the bugs were equipped with thicker shells, more resilient nerve cells and an enzyme that helps break down toxic substances. Now, New York City hosts super-strong bedbugs that are 250 times more resistant to pesticides than bedbugs in Florida, according to Mental Floss.

Tawny owls in Finland adapted their coloration in response to warmer winters. The owls are either pale gray or reddish brown. Previously, more owls were pale gray, which helped them avoid predators by blending in with the snow. According to Discover Magazine, a 2011 study revealed that while temperatures rise and theres less snow in Finland, more Tawny owls are brown. As winters are becoming milder, natural selection is favoring feathers that camouflage with the brown forest instead of snow.

In stable conditions, theres no reason for a species to change. If there is a major change to the environment, such as new predators, human interference, an invasive species or rising temperatures, then the species will adapt and evolve. Natural selection will favor the animals that are better suited for surviving the new environment.

Climate change is placing environmental stressors on animals right now, therefore several species are evolving faster than ever before.

We can see that animals have evolved in our lifetime, and humans are still evolving, too. Were not a perfect species, and even if we were, new environmental pressures could make us favor certain traits. Some evidence for current human evolution includes a reduction in Alzheimers genes, the ability to digest cows milk and Dutch men getting taller, according to Popular Science.

Evolution isnt just part of our history; its happening right now, to all sorts of species, even our own. Its just easier to observe these changes in animals that have shorter lifespans because we can witness their generational turnover.

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