Lichen as the common ancestor of all life on earth

A satirical April Fool's post from user 'eukaryote' on the rationality forum LessWrong has gone viral by proposing a radical revision to the tree of life. The post, titled 'Lichen as the common ancestor of all life on earth,' humorously posits the 'Big Lichen' model, arguing that the Last Universal Common Ancestor (LUCA) was not a simple, single-celled microbe but a fully formed lichen. This framework inverts standard biology, suggesting that fungi and cyanobacteria are actually 'diminished' or partial forms that broke off from a more complex ancestral lichen organism, from which all other life, including animals, descended.

The post is a clever piece of speculative fiction that critiques the genuine complexities of abiogenesis—the origin of life from non-living matter. It highlights the 'deeply unlikely' simultaneous emergence of genetic replication, metabolism, and cellular structure required by mainstream theories. By contrast, the fictional 'Big Lichen' model presents a self-sustaining system needing only sunlight and rock, simplifying early reproduction and dispersal. The satire extends to evolutionary principles, noting it's 'much, much easier for natural selection to break a system than to build a new one,' using examples like parasitic simplification to bolster its absurdist logic. While purely a joke, it engagingly mirrors real scientific debates about life's earliest, evidence-scarce epochs.