Evolution can and has been observed
The theory of evolution explains how living things change gradually over generations to adapt to their environment. Even though evolution happens bit by bit, we can see it all around us, both in the lab and in nature.
What is the theory of evolution? ‘Evolution’ means small changes that happen over time. Biologist Dr Kathryn Hall likens evolution to being ‘a lot like the old parlour game of whispers, you start out saying "the rose is red" and by the end of the game it is "the goat is dead" or something like that’. We sometimes talk about the evolution of cultural things like language or music, as well as the scientific ‘theory of evolution’.
The theory of evolution was developed by Charles Darwin to explain what he saw whilst sailing around the Galapagos islands - finches had different beak shapes on the different islands. Even more surprising was that their beaks matched the kind of food that was available on that island. The finches on the islands with lots of insects had needle-thin beaks, whilst those on the islands with large seeds and nuts had much broader beaks.
What was Darwin's explanation? Baby finches are always a little bit different from each other and their parents (just like us). Some finches might, by chance, be born with a beak that is perfect for the environment they are in. These finches eat much better than their friends, and are more likely to survive into adulthood and have lots of children of their own. Bit by bit, eventually most of the finches on the island will have that kind of beak. This process is called ‘natural selection’ or ‘survival of the fittest’, and is the basis of how evolution works.
Side note: scientific theories It's important to note that the ‘theory’ of evolution was developed to explain something that exists in the real world. Darwin developed the theory using not just finch beak data, but data he collected from many animals whilst sailing around the world. On top of that, another scientist, Alfred Russell Wallace, also came up with the same explanation completely independently. The theory of evolution is supported by lots of examples from the real world (see below). As evolutionary biologist Dr Travis Hagey explains: ‘[in science] a theory is a broad explanation based on years and years of experiments ... For example the theory of gravity, the theory that bacteria and viruses make us sick, the theory that material is made up of atoms, and the theory of evolution are just a few.’
What's the Evidence for Evolution? Even though evolution happens over generations, there are many examples where we can see it in action. A great example is the peppered moth in the UK, so called because of its white appearance with black speckles. Between 1848 and 1895, the population of peppered moths that had completely dark wings rose so much that they became much more common than the original white version. At this time, the industrial revolution was happening in the UK, leading to air pollution which made tree surfaces, which the moths rest on, dark in colour. This meant that the darker moths were better able to camouflage and hide from predators. Interestingly, since some laws have reduced the amount of air pollution in many places in the UK, the original white speckled moth is becoming more common again.
Evolution happens over many generations, so to see it in animals like moths or chickens you need to collect data over many years. Organisms like bacteria and yeast grow and breed very quickly (in minutes or hours), which means we can see their evolution in the lab over much shorter timescales. Expert Richard Edward observes how, over many generations, yeast in his lab can evolve to grow in an environment that it originally couldn’t survive in. In the same way, evolution means bacteria can become resistant to antibiotics. This is seen in patients in hospitals, and can also be recreated in the lab - captured in this video from the Kishony lab in Harvard.
A world without evolution? Apart from the ones shown here, there are many examples of evolution in plants, animals and bacteria. All of these observations fit with the theory of evolution - it is our best explanation of what is happening, just like the theory of gravity is our best explanation of why things fall to the ground. As ecologist Dr Ross Alford puts it: ‘The notion that evolution is random and unobservable is not supported by science at all; in fact science demonstrates clearly that it is lack of evolution that is impossible.’
Takeaway: Charles Darwin developed the theory of evolution to explain what he saw in nature. Over 150 years later, gradual changes that we see around us - in moths, chickens, bacteria and more - still fit perfectly with this explanation.