Big brains vs little brains in marine life

The wonderful biological computer we call the brain has allowed the human race to develop and build the safe, comfortable, technological society we live in today, a society in which comparatively few of us are forced to fight tooth and nail for survival on a daily basis.

In the undersea world, however, the art of survival is still the key to avoiding a premature death, and the key to survival for many animals is intelligence.

That said, there’s no universally accepted definition of non-human intelligence or any universal procedure for measuring it.

A big brain doesn’t necessarily put you at the top of the survival tree. The largest brain in nature belongs to the sperm whale. Its brain weighs around 7kg, which is five times the average weight of the human brain. A great white shark, arguably a great survivor at the top of its food chain, has a brain weight of only 35 grams.

What is more important than brain size is how you use your brain. We can get a better idea of an animal’s level of intelligence by looking at the speed and success it demonstrates in solving problems.

At S.E.A. Aquarium we can see an array of marine animals that possess a range of brain complexity, from the most complex shark brain to sea jellies with no brain that we know of.

The clever invertebrate

An octopus in camouflage

Octopuses don’t have the largest brains in nature, but they do have the largest brain cells.

An octopus brain is formed by 500 million large neurons, three fifths of which are in its eight arms. In comparison, the human brain has 100 billion small neurons.

The octopus shows a high level of brain organization by being able to coordinate its thousands of colour changing cells. The brain sends out orders in response to threat, and the arms execute the orders, changing the appearance of the octopus and camouflaging it to escape the threat.

Most complex brain

Shark Encounter_3

A shark’s intelligence is demonstrated by its ability to assess a situation, and make a super fast decision based on that assessment.

People tend to believe that sharks are very primitive because they only have small brains, but the truth is we still understand very little about them.

We do know that reef sharks and hammerheads have the most complex brains. They use their complex brains to process information from their highly developed senses, allowing them to detect prey and identify suitable mates.

Sharks can also use the earth’s magnetic field to navigate under the sea, which must be like having a GPS unit in your brain!

Biggest brain to body ratio

Giant Ocean Manta Ray

Manta rays have the highest brain to body ratio of all fish, comparable to a similarly sized mammal. A large part of a manta’s brain has been shown to be responsible for higher functions, including efficient sensory functions.

They also have a specialized network of blood vessels around the brain that help to protect it during deep dives, when the temperature of the water drops rapidly.

Unique brains

comb jelly

Comb jellies-mba” by Steve Jurvetson

Researchers have found  that by studying comb jellies they are one step further in finding treatments for Parkinson’s, Alzheimer’s and other neurodegenerative diseases.

Current treatments can slow down brain degeneration, but can’t reverse it. The comb jelly, however, has a completely different chemical language from other animals and this unique chemical language allows the jelly to regenerate at will.

Now we know that neural systems can be constructed differently, decoding the jellies’ language should help us to develop regenerative medicines for human beings with brain damage.

No brain

Sea jelly at S.E.A. Aquarium

Sea jellies are more than 90% water, together with a gelatinous substance that gives them structure.

While it is true that they do not have a brain as we know it, these ocean drifters have a ring of nerves called a nerve net, which transmits information about its surroundings throughout the jelly’s body.

Now that you know which are the brainiest animals at S.E.A. Aquarium, visit and see them for yourself at the Aquarium.

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