Since the words “animal” and “plant” are both man-made, and their definitions are completely artificial, they are obviously a classification method created by humans to make the world easier to understand. The key lies in what standard we set. Our criterion is whether an organism is heterotrophic or autotrophic: animals cannot produce organic matter themselves and must take in other living things or organic matter as food; plants mostly contain chlorophyll and can carry out photosynthesis, using light energy to combine CO₂ and water into organic matter and make their own nutrients. But if you know about certain organisms, this boundary is blurred. For example, euglena can be called a transitional form. If this classification had never existed in the world, we could completely set our own standard, such as whether something can be eaten by humans. Of course, we can also ask ourselves: what is the difference between humans and animals? Do humans belong to animals? If humans do not belong to animals, then is Quasimodo a human or an animal?

Both, but for basic classification it leans more toward “discovery.” When biologists classify species, they are identifying real evolutionary lineages—groups with a common ancestor and clear genetic boundaries. These are “natural” and existed before humans gave them names. Similarly, the periodic table reflects real patterns in atomic structure. However, the boundaries and levels we impose (species vs. subspecies, kingdom/phylum/class/order, etc.) involve human judgment. Nature does not always provide clear-cut boundaries, so we create classification systems—but we also discover the underlying patterns that they map onto.

I think it is the latter. Nature itself does not draw clear dividing lines between species. Categories like kingdom and species are all created by humans. These groupings are tools that help us study organisms and understand life. Although differences between organisms objectively exist, the boundaries we draw are artificial, set for our convenience in research.

They are basically invented. For example, ancients held that solids and liquids differ in essence, but in contemporary physics both (along with many others) belong to condensed matter.

Humans create a way of classifying things that makes the world easier to understand. Even setting everything else aside, it is very hard to define what is a plant and what is an animal—the euglena is a very interesting example.

Scientists discover real biological patterns, but humans choose how to name and group them. Classifications therefore reflect both nature and our purposes.

I think many people would say these categories are only a way of accounting for our understanding of nature. But now I want to share a very different opinion. Those classifications devised by humans are indeed better for us to explore further, because most humans prefer organized systems. But think about it another way: we have more than one way of classifying things, and we may already form a complex system that accounts for most of the relationships and properties we know. As we learn more about nature, we might be able to form a very complete and complex classification system that nature itself tends to form by. Additionally, there is never a naturally existing classification; this world is somehow mysterious to us, so we never know.

Biological relationships do exist independently of human existence. For instance, organisms inherit their DNA from their ancestors, and thus organisms with a recent common ancestor will be genetically similar. The evolutionary connection between humans and chimpanzees was not created by man; rather, it was observed in the evidence that scientists found. Biological classification in the modern sense is based on objective facts about nature, including evolution and common ancestry.

Yet there are aspects of the classification scheme that are invented by humans. Nature did not label organisms as belonging to different species, genera, families, and so forth. This scheme was devised by scientists in order to classify the enormous amount of biological diversity that exists. The concept of a species itself becomes problematic. According to the biological species concept, species are classified according to the ability to produce viable offspring, which, however, cannot be applied to asexual organisms, fossil organisms, and occasionally hybridizing populations.

One particularly intriguing case is that of ring species. Let there be populations A, B, C, D, and E geographically spread out. A can mate with B, B with C, C with D, and D with E—but possibly not A with E anymore. Where then is the point at which we can draw the line between one species and two? The organisms are real, but the border is a scientific choice to make.

This provides an insight into the fact that classification can be objective even if it is not entirely natural. An illustration is the use of maps. Mountains, rivers, and coasts are real, whereas nations’ boundaries and choices for map symbols are not—they are human creations. So is biological classification: the relationships are the landscape, taxonomy is the map of it.

Historical considerations are also relevant here. Earlier classification methods were based largely on visible features, so organisms that resembled each other were often grouped together. But it was later discovered through DNA sequencing that appearances do not tell the whole truth, as unrelated organisms can develop similar features through convergent evolution. This suggests that categories in science cannot simply be invented, but they can be verified and adjusted when our categorizations prove to be poor representations of nature.

The most intriguing thing about this philosophical consideration is that the question poses a false dichotomy between “discovered” and “created.” Scientists may be creating categories in order to discover some patterns. But the categories themselves—the concepts of genus and family—are products of human intelligence, while the very structures they describe have been around for a much longer time than humanity.