What does 'evolution' even mean?
If you've been interacting with creationists in online spaces you've probably stumbled upon an argument akin to "I don't believe in evolution! I believe in adaptation!". It is also common for them to incorrectly equate microevolution with adaptation and conflate macroevolution with universal common ancestry. To clear up this confusion I decided to create this post.
So, what even is evolution?
Evolution (as a process) is commonly defined as changes in heritable traits in populations over generations. It is also frequently referred to as descent with modification since every organism is simply a modified version of whatever its ancestors were. It is thus incorrect to claim that evolution is one organism undergoing some kind metamorphosis-like transformation causing its biology to be completely rewired. It, similarly, can't be treated as one organism giving birth to an offspring of a completely different order, class or any other high taxonomic level. It shouldn't be conflated either with origin of life from non living matter (abiogenesis). Of course, evolution occurs not only in living organisms but also in viruses, viroids and obelisks and because of that evolution probably was a part of origin of life as it almost certainly wasn't a spontaneous event but a gradual process. Abiogenesis still shouldn't be conflated with evolution since it would involve prebiotic synthesis of peptides, RNAs and other biomolecules which does not fall under the definition of evolution. Aside from that, even if we had no idea on how life came to be it would not impact the validity of a claim that all living organisms are related as each of these ideas is determined upon different lines of evidence. Dear creationists, because of that, you can't say that origin of life and the big bang are a part of evolutionary theory.
Since evolution is defined as gradual changes over successive generations, any example regardless of taxonomic level is an example of it. Because we've mentioned taxonomy it is worth bringing up the distinction of macroevolution and microevolution. Microevolution is a term to describe evolution occuring within species. Examples of microevolution include emergence of new subspecies within the same species, population adapting to a local climate or selective breeding of domesticated animals. Macroevolution on the other hand means evolution at the level of species or above it - emergence of new species (speciation), new genus, new phylum etc. are all examples of it. Claiming that macroevolution is inherently defined as "origin of new kinds" is simply incorrect if not disingenious as this is not a common (let alone a scientific) usage of this term. Macroevolution is also frequently mistakenly conflated with the notion that all organisms share a common ancestor. While all organisms descending from a common ancestor can be considered an example of macroevolution since it involves evolution above species level they are still not the same since macroevolution occurs every time speciation does. It's also worth noting that macroevolution can sometimes have different meanings in the scientific literature. However, it is not defined in the previously mentioned way creationists use it. The reason I decided to include a taxonomic-level-based definition is because it is the most common one and creationist definitions are also usually related to taxonomic levels (albeit in pseudoscientific manner).
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Independent acquisition of three color vision amongst primates as an example of macroevolution
Now let's bust a common creationist misconception regarding adaptation. Adaptation (as a process) is defined as groups of organisms becoming better suited for their environments/niches over successive generations due to natural selection. Adaptation (as a trait) is a feature that allows organisms to be suited to their niche/environment. As you can see, there is no sentence nor word equating adaptation with microevolution (as creationists frequently do). That's because evolution at any taxonomic level can be adaptive or non-adaptive. An example of macroevolutionary adaptation is the acquisition of echolocation among different animal groups. Since echolocation is helpful in, for example, hunting or traversing terrain it certainly is an adaptive trait and thus evolution of echolocation is an instance of macroevolutionary adaptive process. When it comes to microevolutionary adaptation, a common cited instances involve antibiotic resistance in bacteria. This trait is clearly adaptive as it is routinely developed in response to harmful results from coming into contact with antibiotics. Major mechanisms include mutational resistance and horizontal gene transfer.
When it comes to non-adaptive examples of macroevolution the best one is the transition from "simple" multicellularity to "complex" multicellularity in eukaryotes. While aggregating in groups of many cells is adaptive (as it can protect against predators and so on) the origin of much more complex forms of multicellularity probably stems from eukaryotic tendency to accumulate mutations leading to the expansion of the genome with "DNA junk". This tendency manifests as a response to genetic drift (random changes of traits in a population). While prokaryotes (bacteria and archaea) tend to accumulate deletions as a result of random population changes, the opposite is the case in eukaryotes, which accumulate mutations causing the expansion of genome size. This non-adaptive tendency probably allowed multicellular eukaryotes to accumulate new sources of evolutionary novelty and thus new sources of information necessary for evolution of different cell types, tissues etc. It is worth noting that this isn't "just a coincidence" but rather a non-adaptive byproduct stemming from different adaptations already present in prokaryotes and eukaryotes.
Different types of parenchyma tissue in wood
In order to find a microevolutionary example of non-adaptive changes, we don't have to look far, as any example of observed genetic drift falls into this category. One interesting example is that of the Amish population that migrated to Pennsylvania in 1744. Due to small population size and high levels of isolation, alleles causing Ellis-Van Creveld syndrome had spread much more effectively in this population, leading to a higher frequency of occurrence of Ellis-Van Creveld syndrome among Amish population compared to the general American one. Because of that it makes no sense to equate microevolution with adaptation and macroevolution with completely random changes. And that leads me to an advice: if you're a creationist just say something akin to "I accept evolution but only at low taxonomic levels". This statement will be much more in line with definitions even if it won't be scientifically correct as evolution at any taxonomic level is well-supported by the empirical evidence.
A photograph of Titicaca water frog. I'm putting it here because I recently learned about the existence of this peculiar aquatic amphibian.
Sources:
1. Evolution: https://en.wikipedia.org/wiki/Evolution
2. An introduction to evolution: https://evolution.berkeley.edu/evolution-101/an-introduction-to-evolution/
3. Biology and evolution of life science: https://pmc.ncbi.nlm.nih.gov/articles/PMC4705322/
4. Abiogenesis: https://en.wikipedia.org/wiki/Abiogenesis
5. Viral evolution: https://en.wikipedia.org/wiki/Viral_evolution
6. Understanding viroids, endogenous circular RNAs, and viroid-like RNAs in the context of biogenesis: https://pmc.ncbi.nlm.nih.gov/articles/PMC11210808/
7. A novel viroid-like RNA element “Obelisks”: a major breakthrough in the RNA World: https://pmc.ncbi.nlm.nih.gov/articles/PMC12226432/
8. Microevolution: https://en.wikipedia.org/wiki/Microevolution
9. Macroevolution: https://en.wikipedia.org/wiki/Macroevolution
10. What is macroevolution?: https://evolution.berkeley.edu/evolution-101/macroevolution/what-is-macroevolution/
11. Common descent: https://en.wikipedia.org/wiki/Common_descent
12. Adaptation: https://en.wikipedia.org/wiki/Adaptation
13. Decoding the functional adaptation of animal echolocation: a global macroevolutionary analysis: https://link.springer.com/article/10.1007/s11427-025-3183-x
15. Mechanisms of Antibiotic Resistance: https://journals.asm.org/doi/full/10.1128/microbiolspec.vmbf-0016-2015
16. A nonadaptive explanation for macroevolutionary patterns in the evolution of complex multicellularity: https://pmc.ncbi.nlm.nih.gov/articles/PMC10873551/
17. Genetic drift: https://en.wikipedia.org/wiki/Genetic_drift
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