From the Citiot Desk

A Pretty Big Story


In my last few messages, I shared my love for math and engineering. This time I hope to share the love that actually did capture my heart way back when—biology. I wanted to understand myself, my family, and all the rest of us. It seemed to me that my only chance was to understand all the rest of life, to see who we are by seeing who we are not.

I spent a little time learning about proteins and DNA, viruses and bacteria, but the deepest questions for me start at how cells organize themselves into animals. Each cell has the same DNA, yet they all make different decisions about what to become: skin, liver, brain. How in the world can that happen?

Well, first, when did it happen? About 500 miles northwest of here the Canadian Rockies rise thousands of feet above sea level. About 500 million years ago, that land was a clay sea bed, and the sea was full of life. About 100 years ago, a guy from the Smithsonian had heard about workers on the Trans-Canada railroad finding “rock bugs.” He rode west to check it out and changed biology forever.

What he found, the Burgess Shale, is the legacy of the Cambrian Explosion—fossils of an enormous array of animals. Virtually all modern forms of animal life are there, including our ancestors, the chordates. You’ve maybe seen some modern cousins of our phylum; we call them sea squirts. Though they look nothing like us, they have immune and nervous systems very much like our own, and most significantly they have notochords, which are the beginnings of our backbones. By 500 million years ago, cells clearly knew how to organize themselves into very complex animals.

But let’s look at another group abundant in the clay, the cnidarians. They can teach us something important about who we are and maybe even why. You’re familiar with their modern cousins: jellyfish, corals, and sea anemones. One thing all cnidarians share is the stinging cells they use to capture and paralyze their prey. You might easily see other similarities; they all have tentacles. The jellies let them hang down as they float about, the corals and anemones hold their tentacles up in the current. What you may not know is that for many cnidaria, these two life forms are just two generations of the same animal, twins conjoined by time.

Turns out, these are two fundamental strategies for life as a cnidarian, each successful for at least half a billion years. One is to float on the ocean currents, traveling the world and finding food. The other is to sit and wait, letting the world’s oceans bring food to you. Some species, the scyphozoans, are specialized vagabonds; others, the anthozoans, stick to the rocky ground. Each form feeds and reproduces in its type, either by shedding sperm and eggs or by laceration, wherein chunks of tissue get torn away, reorganize their tissue, and form whole new animals.

A third class of cnidaria reveals an important evolutionary lesson. The hydrozoa alternate traveling and sedentary life forms. A tree of polyps grows on the ocean floor, communally feeding on whatever gets trapped by the colony, then when the time is right, they create special branches that form jellyfish, which then launch themselves into the deep, spreading their lives on the currents, to shed sperm and eggs colonizing new territory. The fertilized embryos settle to form a new community of polyps.

It’s not trivial to prove, but I think this is the primordial life cycle, and the anthozoa and scyphozoa have simply specialized, leaving one or the other life forms behind. Just to illustrate the drive of evolution, consider the Portuguese man-of-war, a colony of polyps that builds a raft to hang from, combining the strategies of their cousins. Life tries everything.

So, what do we learn about people? First, of course, people are unique among animals in many ways, but one important distinction is that we take so long to become reproductive. Fifteen to 20 years is common. I was 42 when I first reproduced. Absurd. Why?

I think it’s because the world we live in is very complicated and always changing. We’re not born with the knowledge it takes to succeed, so we give birth to these lovely little worms that know nothing and can do nothing. We feed them, protect them, and teach them because while we share two requirements with cnidaria, eating and reproducing, we have a unique third requirement: adapting, and a new post-reproductive life stage, which I now inhabit.

There is a place in our village for folks who remember. I’m grateful that the joy of eating spans the whole of our lives, and I’d like to believe that learning lasts a lifetime, but we too often separate functions in time, specializing to fit each purpose. Early in life, we usually stay close to home, growing and learning. At maturation, we often travel, learning more and maybe finding a new home. Lastly, we settle down with children of our own, mostly teaching and, if we’re lucky, learning too.

Of course, we aren’t cnidarians, rigidly locked into roles dictated by our bodies, but it’s comforting to me to find some commonality, to recognize that life has some general order and that we are part of a pretty big story.

Jack Dunne lives gratefully in Lakebay.