There are three domains that evolved from the last universal common ancestor for all life on Earth: Archaea, Bacteria and Eukaryota. Eukaryota contain all organisms with membrane bound organelles (like a nucleus) which can be further classified in to 4 main kingdoms: Fungi, Plantae, Protista and Animalia.
These kingdoms can be further organised into a number of phyla. For example, All vertebrates such as ourselves come under Chordata. However, the octopus – being an invertebrate – is under the phylum of Mollusca where soft-bodied and mantle-owning creatures are found. It is thought that the first mollusc evolved around 530 million years ago, although the history behind them is uncertain since most soft-bodied creatures don’t leave fossils. Some molluscs used (and still use) hardened structures of calcium carbonate which is why we have evidence of their evolution.
Mollusca can again be organised into classes. Octopuses are found under Cephalopoda; this literally translates from Latin to ‘head foot’ where their heads are directly connected to their feet – in the octopus’s case, these are arms. Subclasses of the cephalopods are shown as below:
Other classes of molluscs are Gastropods, Chitons and Bivalvia.
Around 300 species of octopus have been discovered and in comparison to other animals, they’re evolving incredibly slowly. The majority of these have existed for at least 300 million years (for contrast, modern humans have only been around for roughly 300 000 years).
Cephalopods have a strange way of adapting to their environments. With almost all other Eukaryotes, mutations mostly occur in the DNA, which is transcribed to RNA for protein synthesis. The altered proteins produced that are better suited to the organism are inherited through generations, leading to new characteristics and over a very long time period, new species. Cephalopod mutations, however, mainly occur through ‘RNA editing’ (particularly A-to-I editing) where they can change the proteins found in their bodies without undergoing mutations to their DNA. This happens when the enzyme ADAR2 removes a nitrogen and two hydrogens from adenosine to form inosine.
RNA editing results in the original DNA is conserved, and yet cephalopods can still adapt to their environments at a speed quicker than those relying on DNA mutations.
It is likely that this ability developed because of the frequency of ocean temperature fluctuations. Cephalopods have to match the speed at which their environment is changing in order to survive.
REFERENCES
Curiouser and Curiouser-Octopus's Evolution Is Even Stranger Than Thought
Bret Stetka
Date published: 13th July 2023
Date reviewed: 19th December 2023
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