From Cells to Organisms—When One Plus One Equals More Than Two

Episode #8 of the course How the cells work by Luis Francisco Cordero

What is better than a cell? Two or more cells working together, of course. Multicellularity is a feature that developed many times during the evolutionary history of life on earth and conveyed important advantages.

When you have many cells working side by side, some can disregard a few functions, while other take them to the extreme of specialization. For example, while a set of cells can devote themselves to the protection of the whole organism, others can let go of their defensive strategies and allocate more effort to become experts in the digestion of nutrients, detection of luminous or acoustic stimuli, and even sexual reproduction, which we will talk about more tomorrow.

Multicellularity is the main feature that helped fungi, plants, and animals to exist, and the complexity we see in them is way beyond the scope of what a single cell can attain. Single cell organisms do communicate between themselves chemically, just in a very simple fashion.

Better, How?

But is this truly better? Well, it’s hard to tell. Although it is impossible to deny that multicellular organisms can attain a level of complexity that free-living cells can only dream of, this does not necessarily imply that they will be more successful.

And this takes us deeper in the philosophic discussion of life and evolution. What, exactly, is more successful here? In the big scheme of things, life’s success is established only by its capacity to sustain itself through time. In other words, for any kind of organism, its victory will be determined by the ability it possesses to survive, generation after generation. So far, bacteria have survived many—and will probably survive many more—different organisms, even multicellular eukaryotes such as ourselves, so we should not call them “inferior” beings just for lacking a nucleus … or you know, brains and such.

Did You Know?

When you are constituted of many cells, some of them have been programmed to exist for a while and then die for all of them to thrive. This seemingly counterintuitive fact is nevertheless of the utmost importance. In fact, one of the most deadly diseases that affect humanity has to do with cells that simply won’t die when their time is due.

Cancer, put simply, is what happens when a cell that should have ceased existing “rebels” and stays alive. What’s more, these kinds of cells begin replicating at a higher pace than usual, resulting in a cell conglomerate, and sometimes they even detach from their original site and travel to distant locations, disrupting those organs where they land. This seeding of cancerous cells far from where they originated is what we call a metastasis.

Key Takeaways

Some cells live by themselves, collaborating to some extent with others. But at various points during evolution, different kinds have gone one step further and found an advantage in being closer together. Multicellular organisms have different kinds of cells, and this unification of many allows each one to become experts in smaller tasks that collectively give birth to complex creations such as a flower, a fungus, a ferret, you, and me.

Tomorrow, we will see how having many cells became a canvas for another very important complex life feature: sexual reproduction.

Recommended book

The Emperor of All Maladies: A Biography of Cancer by Siddhartha Mukherjee