Let me start with a disclaimer: When I speak of “purpose” in this essay, I’m not referring to living a life of purpose, a fulfilling life. That will be the topic for another time. Today, we deal with the question of whether life on Earth, from its primal beginnings to the advent of Homo sapiens and beyond, has a goal and whether we are it.

There is a bit of confusion from the start. Life, after all, is not an entity with a specific agenda. We can’t claim that life as a whole has a sort of hive mind, a kind of intelligence with a plan, a place to go. This would be more belief than science—that there is a teleological purpose at work, with the means (evolution of life on Earth) justifying the end (us). Many people, including some prominent scientists, believe this, but we have no concrete proof. (Editor’s note: Denis Alexander is one of those scientists; read ORBITER’s interview here.)

Instead, at its most fundamental, life is the property of a complex network of biochemical reactions—to both interact with the environment so as to metabolize energy, and to reproduce itself via natural selection. In simple terms, life is a kind of hungry chemistry that is able to duplicate itself. This chemistry can go from very simple (a single-celled organism) to complex (a lobster or you).

There is, however, something quite remarkable about life, and that is that all life on Earth is interconnected in a very fundamental sense. Quite beautifully, all life, from plants to insects to humans, shares a common ancestor known as LUCA (Last Universal Common Ancestor), dating to around 3 billion years ago.

According to modern biology, and as Darwin had intuited in On the Origin of Species, the mother of all life forms was a simple bacterium. LUCA was our microbial Eve.

There were, very possibly, other life forms before LUCA. We don’t know exactly who LUCA was, or when it thrived. But paleo-biologists—scientists that investigate creatures that lived a long time ago—have succeeded brilliantly in mapping life’s evolution from bottom-up in extraordinary detail, especially considering the difficulties in finding fossil evidence of living creatures from billions of years ago. Instead of looking for bones or imprints in rocks, to find LUCA they look at DNA. They are able to trace LUCA to a simple prokaryotic creature (a single-celled bacterium with unprotected genetic material). It must have been a very tough organism, able to survive in very extreme environments. Staying alive has never been an easy job.

The question many have, especially once we learn about LUCA, is whether there is an objective to life. The dogma of biology, for decades, has been that there is no such thing. Life evolves through random mutations in the genes. Some of these mutations, once expressed in the organism, may be beneficial to its survival while others will not. The vast majority of mutations are very bad. Occasionally, however, a mutation will lead to a selective advantage: the mutated organism will be faster than his peers, or stronger or smarter, and this will allow it to live longer and reproduce more, hence leaving a progeny of powerful little mutants. In time, a long time, the whole species may be very different from his ancestors many generations back. Clearly, LUCA is the prime example of what mutations can do.

Survival is the purpose

According to the dogma, then, life has no purpose, apart from survival. Time passes, organisms mutate, fight for food and shelter, and those with higher survival chances prevail.

In the long history of our planet, cataclysmic events have wiped out a large fraction of living organisms. There have been at least five huge extinctions and, according to some scientists, we are living through a sixth one, largely man-made, as powerfully documented in The Sixth Extinction, the Pulitzer-prize winning book by Elizabeth Kolbert. Usually, these mass extinction events are caused by radical environmental changes: volcanic eruptions with global reach, comet or asteroid impact, pollution and territorial encroachment.

From the angle of mass extinctions, the question of life’s purpose comes into new focus. Take the dinosaurs, for example. They were happily living here for about 150 million years when, about 65 million years ago, a 6-mile wide asteroid hit the Yucatan peninsula in Mexico. The impact shot so much dust and rocks into the higher atmosphere that Earth got cold and dark for months, possibly years. Plant-eating dinosaurs perished, soon followed by their meat-eating predators. In the oceans, plankton also disappeared, compromising the food chain. Soon, more than fifty percent of life on Earth had disappeared.

If life has a purpose to fulfill, it clearly needs to protect itself against natural cataclysms. Are we, humans, an example of this purpose? After all, we may not be able (yet) to predict and protect ourselves from earthquakes with high efficiency, but we sure have made huge progress protecting ourselves from environmental changes, weather-related events, etc. Unlike dinosaurs, we even have a shot at protecting ourselves from comet or asteroid impacts, given enough notice.

To complicate the question of life’s purpose, the biological dogma has been somewhat revised lately with the advent of epigenetics, which says that genes can be switched on and off. This means that in the long genetic code that makes a living creature, certain genes (chunks of this code) can be turned on or off by different circumstances, not related to random mutations. Genes carry with them the specific instructions for cells to make proteins, complex molecules that carry out life instructions. So, when certain genes are turned on or off, protein production changes and the organism is affected.

Some of these changes may be inheritable, passing to younger generations. (This is the more correct meaning of being an epigenetic change.) However, the changes seem to be only temporary, lasting a few generations before they get turned off again. This is different from mutations in DNA, which are irreversible.

This means that there is another mechanism for genetic “mutations,” which is not random but connected to how populations will adapt, possibly accelerating genetic changes. In human terms, this means your diet, your lifestyle, your activity level, and your social interactions all have potential impact on your gene expression, and some may be transmitted to your children. I used italics here because there is a lot we don’t know about epigenetics and, unfortunately, a lot of pseudoscience is using it as the cure of all evils. It doesn’t seem possible to reprogram your genes with your mind.

So, back to the issue of life’s purpose: Even with epigenetics we must conclude that there is no such thing. Our intelligence is not part of a grand plan, but the result of billions of years of evolution in a complex, changing environment. The purpose we may find in life is a posteriori, the result of our presence on this rare planet.

Now that we are here as an intelligent species capable of self-awareness and of producing knowledge, we should embrace our role as life’s rarest expression and rethink our impact on this planet and the life on it. Being an optimist, I hope that life’s purpose becomes our purpose, as we become life’s guardians and not its destroyers.


For a different perspective, read ORBITER’s interview with Denis Alexander, a molecular biologist who believes that all of life does have a purpose.

Icon-O
Gleiser is a professor of natural philosophy, physics and astronomy at Dartmouth College.