FOR CENTURIES, the traditional way of classifying things in nature was to divide them into three “Kingdoms” – namely animal, plant, and mineral.
Though this is seemingly instinctive, it is certainly not scientific. “Mineral” is now under the physical sciences, such as physics, chemistry, geology, minerology, and so on.
In modern biology, we limit ourselves to the classification of living organisms. That is animals and plants.
Traditionally, animals moved and ate other creatures. Plants were immobile and often photosynthesized, effectively feeding on water, carbon dioxide, and other inorganics.
As microscopes, phylogenetics, comparative analysis proteins and of genes and gene sequence among different organisms, and cladistics improved over the decades, the highest classification for living organisms for a long time was successfully changed.
It was realized that the classification of “animals” and “plants” was severely lacking. Some traditional mobile one-celled animals could both eat other microbes and photosynthesize. Photosynthetic organisms had close cousins that had lost the ability to photosynthesize. And weirdly enough, it was discovered that mitochondria and some other cell organelles had structures which made them resemble bacteria.
So nowadays, living organisms are broadly divided into prokaryotes and eukaryotes. Prokaryotes are one-celled organisms that lack a nucleus, organelles, and other specialized cell structures. Eukaryotes have these. We humans are eukaryotes, as are all traditional “animals” and almost all of traditional “plants”.
It has been theorized since the 1960s that these organelles are actually bacteria and cyanobacteria, that is prokaryotes, that got incorporated into now eukaryotic cell.
In brief, once upon a time, prokaryotes ingested prokaryotes, and instead of the swallowed prokaryotes getting digested, they survived and formed symbiotic relationships with the prokaryotes that ingested them.
Ancient bacteria that could do oxidative phosphorylation became mitochondria, the eukaryotic cell organelle that ultimately oxidizes our food. Cyanobacteria, which are photosynthetic bacteria, became the chloroplasts of eukaryotic “green plants”.
Furthermore, genetic studies have revealed that traditional bacteria included a clade that was far-removed from the others. This clade was dubbed archaea. Thus, prokaryotes are now divided between bacteria and archaea. Archaea are by no means insignificant in ecosystems. For instance, all microbes that can do methanogenesis (produce methane) are archaea.
There are more surprises, waiting especially for the common layperson.
Birds are now classified as part of Dinosauria. That is birds are dinosaurs.
Cetaceans (that is whales and dolphins) are now deemed as deeply nested in the order Artiodactyla, which are the even-hoofed mammals, our familiar cows, carabaos, goats, pigs. Thus, the order of Artiodactyla has now been rechristened into Cetartiodactyla.
As weird as it seems, whales are more closely related to the ruminants like cows, carabaos, and goats than to pigs, within the Cetartiodactyla order.
Termites are now classified as cockroaches. (No wonder cellulose-digesting cockroaches can eat your books and newspapers.) To put it in another way, termites are highly social cockroaches. More on these in future articles. (To be continued)/PN
