Tag Archive | "dolphins"

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What Makes a Brilliant Mammal?

Posted on 21 July 2012 by Jerry

Before the decoding of the genetic content of animal chromosomes, if we wanted to investigate why some animals are more intelligent than others, there were only a few things we could do.  We could observe and test animal behavior under a variety of circumstances.  This might identify which animals are smarter than others.  Then to determine why they are smarter we might surgically dissect them to see if there are physical differences that might explain their enhanced intelligence.

This is exactly what was done in the past.  Through the use of the mirror and mark tests, we identified four mammals (human beings, great apes not including gorillas, bottle nose dolphins, and Asian elephants) that were thought to have greater intelligence and had achieved self recognition.  Upon dissecting and analyzing their brains it was found they each had a highly developed right prefrontal cortex when compared to other animals.  This was assumed to be the origin of their self recognition and enhanced intelligence.  It was also thought to be the reason for their heightened self evaluation, episodic (autobiographical) memory, introspection, humor and empathy.

Today’s geneticists are pioneering the newest methodology.  They compare the decoded genomes of a variety of large brained animals with highly developed cognitive abilities to see if they can determine the genetic roots of the size of their brains and their superior intelligence.  The results of a recent study comparing the genomes of cetaceans (dolphins and whales) with nine other mammals, has shown remarkable genetic similarity among “intelligent” species including primates and elephants.

Although the research, reported in the Proceedings of the Royal Society in the U.K. on June 26, 2012, is still a work-in-progress, it has helped the researchers identify 228 genes that are potentially under positive selection within the dolphin lineage.  This means these genes are becoming more common in the population of cetaceans (dolphins and whales) due to natural selection.  It can also be demonstrated that the overall substitution rate of one base for another inside these genes, in other words the rate of genetic change, has slowed compared to other mammals in the study.  This substitution has slowed to be within the range shown in primates and elephants.  At this point the hypothesis of the study is that the identified 228 genes demonstrate the parallel molecular direction of cetaceans with other mammals possessing large brains.

The study entitled “Dolphin genome provides evidence for adaptive evolution of nervous system genes and a molecular rate slowdown” by Messrs. Michael R. McGowen, Lawrence I. Grossman, and Derek E. Wildman observes that “One aspect of cetacean biology that is striking is the relative size and complexity of the brain, especially in toothed whales (odontocetes).  Similar to anthropoid primates, odontocetes have evolved brains that are larger than expected for their body size….relative brain size….such as in the bottlenose dolphin is greater than in all non-human primates, and sperm whales possess the largest brains in absolute terms.”

This type of research shows great promise for our eventual understanding of the evolution of intelligence.  It also will identify the genetic basis of human evolution that allowed us to become the dominant species on our planet.  It may also one day help us to understand how to insure normal human development or reverse the negative genetic anomalies that cause much hardship for some human beings.

Use the following links to obtain more information on these topics.  I have included an article on the bird species, corvids, because even though we do not understand the avian brain they have shown development of self recognition, hence the use of the picture of a crow in the blog to introduce evolutionary subjects.






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