What makes Living things both Similar and Different?
Why do some people have brown eyes and other people have green eyes? Why do dogs walk on four legs and birds walk on two? Why do horses eat grass and spiders eat flies?
The simple answer to these questions is that all living things, whether they are your best friend or a humpbacked whale, are different from one another.
But what makes us all different?
It turns out that there is a special genetic code that is in all the cells in our bodies and this code is different in almost all living things.
Still, you have probably noticed that even though you are different from your best friend, you are more similar to each other than either of you are to a jellyfish. This is because there are more differences between your genetic code and a jellyfish’s genetic code than there are between you and your friend.
Evolutionary Biologists are interested in trying to understand how changes in the genetic code have made us different from jellyfish, jellyfish different from snakes, snakes different from ladybugs, and so on.
One of the reasons Evolutionary Biologists are so interested in understanding how changes in the genetic code can lead to changes in the characteristics of living things is because scientific research has shown that all living things have evolved from a common ancestor that lived on the earth about 3.8 billion years ago. This means that a very, very long time ago there was only one living thing on earth, but gradually, over many, many, many, many, many, many, many, many, years, mutations that changed the genetic code gave some of these living things new characteristics that helped them to survive and reproduce in new environments and this process led to the evolution of all the diverse living things on earth.
To illustrate how a small change in the genetic code can dramatically change the behavior of an organism, our group brought nematodes to the Science Fair Sunday at “The Children’s Museum” in West Hartford.
Nematodes are round worms that can be either free living or parasites. We used the free-living nematode Caenorhabditis elegans for our demonstration. C. elegans commonly lives in decomposing organic matter, where it eats bacteria. Under laboratory conditions, these worms can display two very different behaviors. Either they eat as a group (clump) and move constantly from food patch to food patch (disperse), or they like to eat alone and stay in the first place they find food. In addition, worms that clump are pickier about what they eat, whereas the solitary foraging worms don’t care.
During our activity, children were allowed to see the differences between these two types of living worms through a compound microscope. We then explained to them that a single mutation in the genetic code (a change in the DNA from T to C) was responsible for the striking behavioral differences. We used a poster board to illustrate in more detail how differences in the genetic code makes each organism unique, how differences between species arise from differences in the genetic code, and how, thanks to our shared ancestry, there are common features to all living organisms.