Cuttlefish Evolutionary History

Cuttlefish Evolutionary History

The cuttlefish are an amazingly developed animal species with many specialised traits that make them perfectly suited to most, if not all, types of underwater environments. This is the animal this presentation will be looking into. Evolution is commonly described as a theory, However that is a common misconception, all different types of evolution, e.g. Darwinism and Lamarckism, are actually considered both fact and theory. As palaeontologist Stephen Jay Gould says in his 1981 book, ‘Evolution as Fact and Theory’, “A scientific theory is a well-substantiated explanation of facts. The facts of evolution come from observational evidence of current processes…” This presentation will delve into the world of the cuttlefish and elaborate how it aligns with Darwinism/Lamarckism.
Jean-Baptiste Pierre Antoine de Monet, Chevalier de Lamarck, or more simply, Lamarck, was a French biologist who is often credited with being the first person to develop a coherent evolutionary theory. Lamarkian Evolution, or as he referred to it, Organic Evolution, is what he described as, in his 1809 published work ‘Philosophie Zoologique’ “The force that perpetually tends to make order.” He asserted that the natural movements of fluids in living organisms drove them toward greater levels of complexity and development. In simple terms this means that, say if a giraffe wanted to reach the leaves higher on the tree, it would stretch out its neck and then that elongated neck trait would be passed on to its offspring who would then in tern stretch the necks longer and so on, until you’re left with an animal with a neck able to reach previously out of reach food. This type of evolution is known today as ‘steady state biology’ and is generally regarded as the foundation for the current theory of evolution, but isn’t quite there yet.
Charles Robert Darwin, or Darwin was an English naturalist and geologist who started his career studying earthworms, until he realised that they didn’t have sufficient traits to make them good candidates for research. Darwin’s key piece of work about his evolutionary theory was ‘On the Origin of Species by Means of Natural Selection’ (1859). In this comprehensive look into the world evolutionary theory Darwin sites finches as his key example of genetic evolution at work. This book was the main piece of work behind the development of the modern evolutionary synthesis. Darwinism, or the now modern evolutionary theory is about how organism’s genes effect the way they grow and develop as a species, e.g. Finches on one island had a short hard beak for cracking open nut shells to get to the goodies inside, whereas finches on other islands had long slender beaks for getting to the nectar at the bottom of flowers, these traits came about because the finches that weren’t suited to the environment died out, however the one’s that could lived and passed on the trait that allowed them to live to their offspring resulting in a new species.

Cuttlefish are a very interesting animal, because they have many uncommon-in-the-animal-kingdom traits that make them ripe for study of evolution. Darwinism is generally regarded as the modern evolutionary theory and is thus the theory that most relates with the evolutionary path of the cuttlefish and any species therein. The cuttlefish is not actually a fish, but in fact a mollusc, and is most closely related to that of squid, octopus, nautilus and snail.
Cuttlefish, squid and octopi don’t have an outer shell, meaning they’ve had to evolve other types of defence against predators. One feature some octopi and squid have is an ink sack and will empty its contents into the water around it allowing the animal to disappear behind a murky cloud, escaping. Cuttlefish on the other hand have developed a much more complicated means of defence. Their skin can change color in the blink of an eye allowing them to blend seamlessly with their environment. This structural adaptation arose in cuttlefish just after Cambrian period. Nautiluses, (cuttlefish’s predecessors) have a large shell that they use for buoyancy and protection. During the Precambrian period there wasn’t many ‘swimming’ fish, any aquatic life were bottom feeders and would stick close to the sea floor. This made nautiluses unique in that they were able to fill chambers in their shells with gasses that would allow them to float away from the ocean floor and thus away from any potential threats. Cuttlefish on the other hand first showed up at around the same time sharks and other large predatory fish came about in the oceans. In order for them to survive they had to develop some serious camouflage, and fast, that’s where their amazing skin came from. It can not only change color, it can also change shape. Cuttlefish, using a muscle pattern along their backs are able to push up bumps and long wavy seaweed-like strands. Once cuttlefish ditched their shell they needed some other way to swim and be buoyant. This caused them to develop a chalk like bone in their backs that stores oils and is used to control buoyancy. They also grew a flap of tutu like skin around their bodies that is used to swim.
Cuttlefish behave differently to their mollusc brethren, because they don’t have the ability to disappear in a cloud of inky smoke when spotted by a threat, they have to use their color changing ability to their advantage. Many cuttlefish will behave like other fish, much in the same way the mimic octopus is able to. Acting like a poisonous tiger fish for example, spreading out their tentacles and changing orang and grey stripped. A particular species of cuttlefish found in Indonesia called the broad club cuttlefish is even known to hypnotize its prey. Changing colors very fast to confuse and stun crabs and other small sea animals to catch and eat.
Overall, cuttlefish’s evolution from the nautilus, loosing its shell, developing a versatile skin and learning to meld themselves to the world around them is most representative of Darwin’s theory of evolution, showing that natural selection is the most reasonable way of explaining how cuttlefish developed and came to be in the world around us.