Chapter 2 starts from the beginning of the universe, detailing how our little plot of space was created and why its conditions were crucial to making it what it is today. To walk you through, 13.77 billion years ago, everything began with the Big Bang. As this novel thing called “time” progressed, we see the creation of the first atoms (hydrogen) and, depending on the density of certain spots in space, small variations overtime could become much more exaggerated and form galaxies. Nuclear fission in stars made new elements, providing us with the chemical evolution that later spawned life. Some of these, mostly iron and silicates, formed Earth 4.5 billion years ago. Both some radioactive elements as well as the impact from Theia (the planet that hit us and created the moon) melted much of the iron and gives us our molten iron core. This is why we have the magnetosphere protecting us from solar wind and along with the ozone stopping UV-C (germicidal radiation) at about 35k altitude. Without it, living cells wouldn’t be able to exist. Additionally, our planet is a “Goldilocks Planet,” as it is in such a position that it is not too hot nor too cold for life. Our axis provides us with seasons, and our moon provides tidal effects in water and rock. Without all this, life would be unlikely to have formed all those 3.5 billion years ago…

Humans have been classifying living organisms since the time of Aristotle; classification helps us learn more about things and the way they work in a system. In 1866, a man named E. Haeckel first made the kingdoms Animalia, Plantae, and Protista. This meant that fungi were often grouped with plants and studied as a division of botany. Then in 1969, R. H. Whittaker decided to split the kingdoms such that there were Animalia, Plantae, Fungi, Protista, and Monera, all of which eukaryotic except the last. Around this time we also gathered enough proof to back the endosymbiosis theory by Lynn Margulis (who apparently was married to Carl Sagan at some point?!?). This theory states that certain membrane-bound organelles, such as chloroplast, mitochondria, and cilia, were actually bacteria engulfed by a different cell with which it formed a symbiotic relationship. Phylogenetics soon replaced regular taxonomy as it was a “natural” taxonomy that relied on evolution to make connections. C. Woese found that small subunit rRNA (ribosomal RNA that is seen in prokaryotes, eukaryotes, plastids, and mitochondria– AKA all organisms), works as a great chronometer, thus letting us create a large-scale tree of life. Since then there have been a variety of theories, such as the first cells more closely resembling eukaryotic cells than prokaryotic, where present day prokaryotic cells simply lost traits along the way, as well as theories that fungi were the first eukaryotic cell.

Studying phylogenetics often requires genetic analyses. The molecules used must be found in all organisms looked at in the study, have similar function, and change at a rate proportionate with how much evolutionary time has passed. SSU rRNA manages this, but only using one gene does not give enough supporting evidence in more detailed cases. ATPase enzymes, for instance, helped us to place that the root of the tree of life is in Eubacteria, meaning that Eukaryota and Archaea are actually sister branches. Of course, other analyses (like aminoacyl-tRNA synthetase, differences in ribosomal subunit composition, and transcription initiation methods) were used to confirm this. Ribosomal gene clusters overall seem to be pretty dominant with fungi. Different rRNA can provide different levels of specificity– 18S rRNA helps distinguish from domains to classes while IGS (intergenic spacer) can distinguish from strains and races, for instance. The point here is we care about homology over analogy since the former shows us genetic roots and can tell us if analogous structures are connected or just convergently evolved. Lastly with this, the further back you go, the more the errors are amplified. Studies using deep time are often prone to err by hundreds of millions of years. A controversial *gasp* comment made is that Archaea aren’t actually bacteria, just as Oomycota are not actually fungi. Our trees are improving and our methods for classification are disproving a lot of commonly held beliefs.

The fungal kingdom is held apart from the animal and plant kingdoms by many things, but most notably by how they get energy and their chemical composition. Fungi absorb nutrients that were digested externally, plants photosynthesize, and animals engulf. Fungi use chitin in their cell walls and ergosterol in their membranes, plants use cellulose in their walls, and animals use cholesterol in their membranes. They have different (or none!) gene sequences for multicellular development. All in all, the kingdoms are different down to a cellular level. Recent research has been revamping the fungal kingdom, removing, adding, and reclassifying species. I am not going to get too detailed with it here since it basically feels like stating scientific names without practical concepts to apply them to, but the book goes over specific examples. Another new taxonimic division are supergroups, an informal way to group species above the kingdom but below the domain level. Two important ones are Opisthokonta and Heterokonta. The first is applied to cells that have or once had a single posterior flagellum and encompasses true fungi and the animal kingdom. On the other hand, Heterokonta have one or more anterior flagella is usually kingdom Chromista (also sometimes called Straminipila, but I am a bit confused on that situation). Some species in that supergroup are protists, brown seaweeds, and parasitic oomycetes.

Fossil records for fungi are relatively sparse due to their poor preservation ability and often have few notable morphological features. Thankfully, those that are well-captured provide us with intriguing information. A Devonian fossil of Prototaxites is about 2 meters tall and can be set apart from plants due to their carbon isotopes (producers have a relatively consistent isotope ratio since they used atmospheric carbon, while consumers have a variable ratio from whatever they digested). Prehistoric fungi were some of the first large terrestrial organisms as about 2 billion years of debris were free for the picking with really no to little competition. Fungal records also flourished after mass extinctions, and are expected to again in the next occurrence. Specimens encased in amber, though, hold slightly more information, showing that many morphological features have hardly changed in millions of years. Fungi’s unique traits give them an unassuming advantage that has kept them thriving. As the books says, their motto is, “if it works… don’t fix it.”

Happy reading,
-Beppa