Question: How did the first multicelled organism evolve when all organisms before it were unicelluar? How did cells suddenly learn to communicate between themselves?

Sara Imari Walker answered on 20 Jun 2011:

Hello Bridget! This topic is still hotly debated. We don’t know exactly how the first multicellular organisms arose and new scientific knowledge is being produced on this topic all the time (I just read a brand new and really cool paper on it just the other day in fact!). To set the stage for what we do know, there are a few important things about single celled life that make it possible for mulitcellularity to arise. For example, bacteria do a lot of neat things, but one of the coolest is that they can actually form colonies that act collectively. Under periods of stress (such as low food supply) bacteria will actually aggregate and even more interesting they differentiate tasks. So they will specialize to do specific roles in the community much like our cells do distinct roles in our bodies as multicellular organisms. So perhaps one of these aggregates was the first step in the path to multicellularity. Although the actually transition is still little understood.

As far as communication, bacteria talk all the time! They just don’t use languages like you and I do. Instead they use chemical signaling. The most famous example is something called quorum sensing where bacteria use chemical signaling to determine how many other bacteria are around. Quorum sensing is one way bacteria can communicate to organize into the aggregates mentioned above. So, basically single-celled organisms can do all kinds of crazy and complex things that we are only now still being to understand. I am sure the others can add more, its pretty fascinating stuff!