A new study co-authored by a geneticist at the National Institutes of Health concludes that life originated elsewhere in the Universe around 9.8 billion years ago – roughly five-billion years before the Earth was even formed. But how did the study arrive at this conclusion, and does it make any sense?
The study, conducted by NIH geneticist Alexei Sharov and theoretical biologist Richard Gordon, operates on a number of assumptions, but here's the big one: life adheres to something resembling Moore's Law, increasing in complexity over time at an ever-accelerating rate. By tracing the thread of genetic complexity back in time, the researchers argue, one can estimate when life originated
Moore's Law, specifically, states that computer performance will double every 18 months, giving rise to an exponential increase in technological complexity. This not only enables us to speculate about the capabilities of future tech, it also allows us to track computer performance back through time and arrive at when that technology first began. In the case of Moore's Law's application to the exponential increase of transistors on integrated circuits, this corresponds to the 1960s, when said number was... well... zero.
In a paper recently posted to the preprint database arXiv, Sharov and Gordon suggest that the origin of life can be estimated by examining genetic complexity through the lens of Moore's Law and backtracking to some point of temporal origin. By tracing the course of evolution over the last several eons – beginning with single-celled organisms and working up through increasingly complex species like fish and mammals – the researchers ultimately conclude that genome complexity has increased exponentially by doubling, not every 18 months as seen with Moore's Law, but every 376-million years.
"What is most interesting in this relationship," the researchers write "is that it can be extrapolated back to the origin of life. Genome complexity reaches zero, which corresponds to just one base pair, at time ca. 9.7 billion years ago... ±2.5 billion years."
Earth is on the order of just 4.5-billion years old. Ipso facto, say the researchers, life originated somewhere besides Earth, evolving not on a geologic time scale, but a cosmic one.
Think that's wild? It gets weirder. Sharov and Gordon go on to draw connections to panspermia, the seeding of life by intelligent aliens, the failures of the Drake equation, and more:
This cosmic time scale for the evolution of life has important consequences: life took ca. 5 billion years to reach the complexity of bacteria; the environments in which life originated and evolved to the prokaryote stage may have been quite different from those envisaged on Earth; there was no intelligent life in our universe prior to the origin of Earth, thus Earth could not have been deliberately seeded with life by intelligent aliens; Earth was seeded by panspermia; experimental replication of the origin of life from scratch may have to emulate many cumulative rare events; and the Drake equation for guesstimating the number of civilizations in the universe is likely wrong, as intelligent life has just begun appearing in our universe.
Look. This is a fun study. It's literally speculating on the origins of life itself – which, from an existential, cosmological, philosophical, religious, exobiological, and countless other perspectives, is kind of a big deal. Maybe the biggest deal. There's talk of panspermia, and aliens, and there's implications for life on other worlds throughout the Universe. It's all quite sexy and fun and interesting. But here's the big upshot, the one that you should keep in mind at all times: biological complexity is a remarkably complex subject.
One thing that worries me about this paper is that it makes no effort, as far as I can tell, to distinguish between complexity and progress, an important distinction that many people fail to recognize. Evolution has no aim, no directionality, no aspirations to "improve." Organisms have been shown to evolve to become more "complex," and they've been shown to evolve to become "simpler" (more on the use of quotation marks in a moment), but never in order to become better, by any objective sense of the word. And while most people who've thought about it probably recognize that complexity does not imply progress or improvement, one of the most common misconceptions about evolution is that it drives organisms toward some sort of ideal. A paper that hinges so fundamentally on a discussion of biological complexity would do well to acknowledge this non-sequitur in a prominent and unambiguous way.
Another issue: the idea that the complexity of life on Earth has increased at the same rate throughout history is highly suspect. The researchers acknowledge this themselves, writing that "there is no consensus among biologists on the question how variable are the rates of evolution." A popular hypothesis in biology known as Punctuated Equilibrium maintains that major evolutionary changes occur during short intervals, interspersed throughout long periods of relative stability. Sharov and Gordon concur that evolutionary rates fluctuate in time, but "strongly disagree" that punctuated equilibrium makes rates of evolution so unstable as to make "any extrapolation of them into the past... meaningless." They disagree so strongly, in fact, that they claim attempts to restrict "the presumed origin of life" to Earth with drastically fluctuating rates of evolution "are strikingly similar to stretching and shrinking of time scales in Biblical Genesis to fit preconceptions." Please.
But the most important takeaway of all – one remarked upon by several peer-reviewed papers on the subject of biological complexity in recent years – is how little consensus there is on what complexity actually is. An excerpt from this 2002 review by Cal Tech's Christoph Adami, a renowned evolutionary theorist and nuclear physicist, summarizes the situation thusly:
Arguments for or against a trend in the evolution of complexity are weakened by the lack of an unambiguous definition of complexity. Such definitions abound for both dynamical systems and biological organisms, but have drawbacks of either a conceptual or a practical nature.
Another excerpt, taken from an article published in Nature in 2008, paints a similar picture of confusion:
In his book Programming the Universe, engineer Seth Lloyd of the Massachusetts Institute of Technology in Cambridge describes how he once compiled 42 definitions of complexity — none of which encompasses everything people mean by that word.
Biological complexity can be defined by cell number, cell type, body plans, gene content, or – in the case of the Sharov and Gordon's work – genomic complexity, "roughly measured by the number of non-redundant functional nucleotides." It can be defined by other things as well. In this sense, Sharov and Gordon's description of complexity as having been "roughly measured," seems rather apt. This study is a fascinating thought experiment, but it – and science's understanding of biological complexity in general – lacks the rigorous definitions necessary for a firm evolutionary hypothesis.