Guest Author - Sarah Meadmore

I’m sure you’ve heard it said - Biology is the study of life. But what is life exactly?

We all know how to tell if something is alive. But do you really know how to explain how you know? You can’t simply say, “It’s moving,” because the water in a river moves. Is that alive?

There are six basic criteria - six questions to ask ourselves - when determining if an object is alive. In order to be classified as living, the object must exhibit the characteristics of all six. For illustration purposes, I will use my dog, Atticus, and a rock.


One: Does it react to it’s environment?

Does the rock react to its environment? No. If it is raining, sunny, windy nothing about the rock changes. If I yell at the rock, it stays the same. While it’s environment might change and cause the rock to be warm (when it’s sunny) or wet (when it’s raining), these aren’t reactions by the rock.

Does Atticus react to his environment? Yes. If there is snow outside, he charges around like a headless chicken. If it is 90 degrees and sunny, he lays in the shade. If I were to yell at him he would lay on the floor at shut his eyes. He reacts to his environment.


B: Does the object adapt to its environment?

Before we get to the rock and Atticus, we need to know the difference between react and adapt.

A reaction is a single behavior in response to a single event. Adaptation is the adoption of a new set of behaviors or physiological characteristics in order to be comfortable within an ongoing change in the environment.

So, does the rock adapt to it’s environment? No

Does Atticus adapt to his environment? Yes. In the winter, he grows a thick coat that keeps him warm. In the summer, he sheds out. And if I were to yell at him all the time, and never use a speaking voice with him, he’d learn to ignore me, or assume that it was normal. He adapts to an ongoing environmental influence.



Tres: Does the object reproduce?

Do rocks reproduce? No. Rocks don’t have babies.

Does Atticus reproduce? No. He’s a boy, and he is neutered. However, his species reproduces. So the question should really be, Do dogs reproduce? And the answer is Yes.



IV: Does the object grow?

Does the rock grow? No. If anything, it is worn down smaller over millennia, by the wind and rain.

Does Atticus grow? Yes. His coat grows, and his toenails grow. At one time, he was a tiny puppy and now he is over 100lbs. He definitely did some growing!



Cinq: Does the object obtain and use energy?

Do rocks absorb energy somehow? No. Neither does the rock use energy.

Does Atticus? Yes, very much so. Atticus obtains energy every day by eating several pounds worth of food. Then he expends all that energy chasing gophers.



Six: Is the object made of cells?

Are rocks made of cells? No. If you were to look under a microscope, you would find that they are not made of cells.

Is Atticus made of cells? Yes. Again, you’d have to use a microscope to make sure. Or you can take my word for it.



So there you have it. You now know how to tell if an object is alive or not.