by James Morris
It’s Halloween, so pumpkins are everywhere. Did you know that pumpkins are berries, but strawberries are not?A strawberry is not a berry. Nor is a blackberry or a raspberry. But pumpkins, cucumbers, bananas, persimmons, and eggplants are all berries.
A berry has a very precise meaning in botany. All true berries develop from a single flower with one ovary. For example, tomatoes and kiwis develop this way, so are considered berries. By contrast, raspberries and strawberries develop from flowers with more than one ovary, meaning that they aren’t really berries, despite their names.
Furthermore, a botanical berry has three layers – an outer skin, fleshy middle, and inner part that holds the seeds, like a grape. These same three layers can be found in bananas and watermelons, which are also berries.
Cherries also have a three-layered structure, but they are not berries because, strictly speaking, berries have two or more seeds. Cherries have just one. Cherries, plums, olives, and other fruits with a central stone containing a seed are called drupes.
Raspberries and blackberries are also drupes. Each of the little parts of a raspberry or blackberry develop from a single ovary and have a central stone with a single seed. This is why wild raspberries and blackberries have a gritty taste. They are essentially multiple fruits (drupes) all stuck together, or aggregate fruits.
Strawberries are also aggregate fruits. However, instead of being made up of many drupes, they are made up of many achenes, the yellow seed-like structures on the outside of the strawberry. In spite of their appearance, they aren’t seeds; they are small, dry fruits each containing a single seed.
This can get a bit confusing, which is precisely what happens when scientific usage differs from everyday usage. This kind of confusion is not limited to berries. Take the word “theory.” In scientific usage, a theory is a broad explanation of a wide variety of phenomena supported by multiple lines of evidence and many experiments over a long period of time. It’s the gold standard in science. Examples include the theory of gravity, the germ theory, the chromosome theory, and the theory of evolution.
However, in common usage, a theory isn’t well substantiated at all. Instead, it’s more like a hunch or guess, as in “I have a theory about why the car won’t start” or “I have a theory about who Snoke is in the most recent Star Wars episode.”
These two different meanings are not just a source of confusion, but are also used to fuel the “controversy” about evolution. In 2005 in Alabama, textbooks included an insert stating that evolution “should be considered as theory.” This statement is factually correct, but intentionally plays with the everyday definition to sow doubt and uncertainty about a set of explanations that are well accepted among scientists.
“Mutant” is another word with multiple meanings. In its everyday sense, we often think of mutants as abnormal, even monstrous, as many Halloween costumes often remind us. However, in genetics, a mutant simply represents a change in the genetic material. Mutations can certainly be harmful, but they can also be neutral and sometimes even beneficial.
With the exception of identical twins, no two humans (or two members of any species) are genetically identical. We all harbor a number of mutations that make us in part different from everyone else. And identical twins accumulate mutations during their lifetimes, so even they are not precisely the same genetically. So, in a very real sense, and in spite of its common definition, we are all mutants.
Although we are all different from one another, we are not that different. In fact, we are 99.9% identical to one another genetically. This means that the differences (mutations) make up just 0.1% of our genetic material. This observation brings us to one more word that is potentially confusing – race.
When we use the word “race” to describe different groups of humans, it draws our attention to our differences. It suggests that there are separate, non-overlapping categories of humans, and the differences between us are great. Belonging to a group can be a point of pride and identity, but it can also be used as a way for one group to exert control over and discriminate against another group.
However, when looked at scientifically, the term “race” is misapplied. We are much more similar than we are different. Human traits don’t map into separate, discrete categories. In fact, there is no trait that everyone in one “race” has and that no one in another “race” has. Finally, there is more genetic differences within any so-called race than there is between races. The genetic evidence suggests that race has no biological meaning, in spite of the power and significance of the concept in everyday life.
While it may not matter whether we know that a pumpkin is a berry, it is important to have a sense of what we know well (theories) and what we don’t (wild guesses). It’s equally important to use terms that reflect our current understanding of science, such as those that describe human genetic variation, not outdated ones that reflect our misunderstandings and even biases.
Getting our words straight should be an easy nut to crack, and is, in a way, low hanging fruit in our conversations about science and the world around us.
© James Morris and Science Whys, 2018