Why are dolphins smarter than most other mammals?

Everyone knows that dolphins are smarter than most other creatures -– but now we have the genetic evidence to prove it. A recent analysis of the bottlenose dolphin's genome has shown that, like humans, a good portion of its genetic makeup is devoted to the development of its nervous system.

The discovery shows that intelligence is a particularly important characteristic for dolphins, more so than for most other mammals.


Dolphins are a particularly interesting species to study, from both an evolutionary and genetic perspective. They are descended from mesonychids, an extinct order of carnivorous hoofed animals that resembled wolves. Their transformation to the sleek, fish-like aquatic mammal that we see today was the result of some fairly extreme modifications. And it's the nature of these variations that's of great interest to evolutionary biologists.

The study of the bottlenose dolphin genome was conducted by a team of researchers at Baylor College of Medicine in Houston as part of a larger comparative study of 29 mammalian genomes. Essentially, the scientists wanted to know how different the dolphins were, from a genetic perspective, as compared to other mammals.

The geneticists looked at over 10,000 genes with counterparts in the genomes of nine other mammals, including humans, elephants, dogs, horses, and cows. What they discovered was that 228 gene sequences were quite different in dolphins, compared to the other mammals. Plus, about 10% of those changes were related to the dolphin's nervous system -– a strong indication that intelligence is a distinguishing and adaptive characteristic for the species.


One group of genes that the scientists uncovered was very much related to a similar set found in humans -– one that's connected to certain brain disorders, like Alzheimer's disease and schizophrenia. This could imply that some dolphins suffer from these conditions as well -– yet another sign that the dolphins' level of conscious awareness may rival that of our own.


Another group of genes appear to be responsible for the forming of synapses in the brain, while another relates to the way that dolphins sleep with one eye open, while one-half of the brain seems to switch off.

Not surprisingly, genetic differences were also seen in dolphin lung development –- a morphological change that was most certainly beneficial for an aquatic mammal. And fascinatingly, the team also found a gene related to hair growth. It's known that dolphins have small hairs when they're calves, but this is likely a vestigial "pseudogene" –- a strong indication that the species was derived from a hairy terrestrial animal.


The researchers also found a genetic similarity that's common to humans and elephants as well, namely a decline in the rate of change exhibited by their DNA sequences over time. This may relate to characteristics such as body size, longevity and generation time –- the time it takes for offspring to mature. This particular finding appears to show that dolphins, humans, and elephants share similar evolutionary pressures.

The comparative analysis of mammalian genomes is available at Nature.

Top image via Shutterstock.com/Christian Musat. Inset mesonychid image via NewAnimal. Inset dolphin image via Nature.


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