The conceit of hindsight.

The ‘ladder of ascent’ fallacy, a common misconception in evolution.

“Life is peculiar,” said Jeremy.

“Compared to what?” asked the spider.

— Men Who Play God (1968), by Norman Moss.

The recent discovery by NASA of the amino acid Glycine in dust from a comet in the outer Solar System has been a shot in the arm to the idea that life here was seeded by organic matter in meteorites, about 3.8 billion years ago. The technical term for this is Panspermia (meaning “seed everywhere”), of which no less a scientist than Francis Crick, co-discoverer of DNA, was an ardent supporter, arguing that the time interval between the formation of our planet and the appearance of life (in the shape of microscopic fossils) was too short for the genetic code to have evolved de novo. Thus, the raw materials must have arrived here from elsewhere in the Galaxy. Many scientists remain unconvinced; and hot on the tail of the aforementioned discovery came the latest hypothesis on life’s terrestrial origins, in transparent Zinc Sulfide ‘bubbles’ which would have allowed access to the energy of sunlight for early replicating matter.

The evidence may never conclusively weigh down on either side, but that doesn’t make this any less fascinating a debate. It’s one of the few ‘big’ questions left in biology, and obviously intrigues us for sentimental reasons. Most people believe that life must be relatively common in the Universe, and we’re rightly excited by the idea of ever finding it, but a real understanding of the science teaches us a word of caution on this front: life may indeed be common, but that doesn’t mean that we aren’t fundamentally “alone” in the only sense that matters to us. It stems from a common misconception about evolution, perpetrated by the Victorians in Darwin’s time and carried through today by human vanity: the notorious “ladder of ascent” fallacy. We wish to believe that, in spite of our unceremonious origins, the entire history of evolution has a pathway paved to our supreme intellect; as inevitable in its trajectory as Newton’s falling apple. But this betrays a crude misunderstanding of the essence of Darwinism: evolution lacks all foresight. It strives for nothing. If we “replayed life’s tape” from the beginning (to paraphrase Stephen Jay Gould), the end result would be strikingly different! Chance trumps necessity in the game of life, and intelligence is no more inevitable an evolutionary invention than the stripes of a zebra.

To convince ourselves than this, we can go one better. Tracing the history of life on Earth as our science reveals it, we can pinpoint the most chance-contingent events, that statistically should have halted the passage to animals, mammals, and humans if we were to rewind the tape and replay it a hundred million times. All complex cellular life is called eukaryotic, meaning “true nucleus”; the genetic material is bound in a membrane-enclosed section of the cell, the nucleus, but the details needn’t bother us here. What matters from our perspective is that without this eukaryotic cell structure, multicellular life could never have arisen on this planet: not so much as a worm or a sponge. The reason for this is simple: eukaryotic cells (but not prokaryotic ones, essentially meaning bacteria) house energy-generating units called Mitochondria inside them. These energy-generating units are the “powerhouses” of the cell, and are present in many hundreds or thousands of copies, depending on how ‘busy’ the cell is in the body; muscle cells have many, bone cells fewer. They take in all food particles, break them down, and give out energy. In contrast, prokaryotes generate their necessarily-limited supply of energy across their external cellular membranes.

We now have very compelling evidence to suggest that these Mitochondria in our cells were once themselves free-living bacteria which entered into a symbiotic relationship with another bacterium. The matrimony produced us; all eukaryotic life. The crucial point is this: the union between the two was contingent on pure chance, it depended on a very particular set of environmental conditions which prevailed in a certain subsection of the Earth for a limited amount of time. It was as far from inevitable as you’ll get. The cells which came together had lived independently for upwards of a billion years and showed no signs of change. Further, no other such union is to be seen between prokaryotic cells now, and none is recorded in the fossil record.

Beyond this, we can point to such events as the evolution of oxygenic photosynthesis and the K-T mass extinction which elimated the dinosaurs (apart, technically, from modern birds). It’s unequivocally accepted that this extincion paved the way for a flowering of mammalian diversity, leading to the Monotremes, Marsupials and Placentals (including us). But the meteorite which struck at that particular time was far from the only such one to ever hit Earth, and we have the similarly-sized crater impacts to prove it. What allowed this particular impact to reek such devastation was no more than a chance coalition of plate-techtonics and the angular rotation of Earth at that point in time; oxygen levels were at an all-time high of 35% according to geologists and so the impact caused massive fire-and-brimstone-esque desolation. The dinosaurs showed no signs whatsoever of evolving human levels of intelligence, and presumably would still happily dominate the land if not for this indifferent meteorite’s strike, with mammals still limited to nocturnal shrew-like creatures that they had been.

The point is twofold. When “moderate” religious people tell us that their theism is entirely compatible with belief in evolution, we should critically analyse this claim in light of what history tells us. Does it seem likely that a beneficent, intervening deity would have been so careless, so capricious in her ‘design’ plan? If any theistic incarnation of god had humans in mind when creating the Universe, she has gone out of her way to conceal this fact, and so it should be surprising that the majority of us confidently affirm this to have been the case. Further, we should proceed with caution when we hypothesise about how plentiful life may be in the Universe, and consider exactly what we mean by this. I can’t deny the romanticism of pointing our radars to the skies and looking for signs of communication in the form of radiowaves, and I’m in awe of Carl Sagan’s pioneering work with SETI (the Search for Extraterrestial Intelligence). Unfortunately, though, it’s difficult to shirk the conclusion that the pervasive image of extraterrestrial civilisations much like our own is no more plausible than a bearded don in the heavens.

by Adam Dinan

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