Wednesday, April 4, 2012

Noses, Their Sense of Smell and How They Enabled Humans to Take Over the World

Out of all the animals on Earth that we know of, we consider ourselves the most intelligent of the bunch, no matter how much we deride and belittle our fellow humans.  However, what was the innocuous event that enabled the rise of complex brains  in the millions of years that life has existed?

For that answer, we need to look back to 195 million years ago, at the Hadrocodium species, what scientists suppose as the first mammal. Measuring at an adorable inch long and weighing just two grams, this  small shrewlike mammal struggled for existence among the giant thunder lizards (dinosaurs).   This creature needed to have some sort of adaptation that enabled it to compete with not just dinosaurs but Lissamphibians (early amphibians) and sphenodonts (lizard ancestors).

 These early mammals evolved  extremely sensitive and pointed  noses that allowed them to scour the night for bugs and avoid their reptilean predators at all times.  While the skulls of these mammals can barely fit on the average fingernail, their brain size to body volume ratio greatly exceeded that of the fauna around at the time.  

Using endocasts (inner cast of hollow objects: in this case, the shrew-like skull), Dr Timothy Rowe observed " enlarged olfactory bulbs, neocortex, pyriform cortex, and cerebellum" in the brain of the Hadocodium.  In essence, the Hadrocodium's nose required a great deal of processing power, encouraging the selection of larger and more complex structures of the brain.

It would not be an exaggeration to say that the usefulness of the nose paved the way for selection for larger brains, which in turn, eventually paved the path for humanity's birth. 

Rowe, T., Macrini, T.E., and Luo, Z.-X. 2011. Fossil evidence on origin of the mammalian brain (Science, 332, 955-957):

Vastag, Brian. "Mammals Win by a Nose: Sense of Smell Drove Evolution of Big Brains."


  1. So mammals have had proportionally larger brains since they first evolved? Neat, although I think it's interesting that increased intelligence wasn't enough to outcompete the dinosaurs since mammals didn't begin dominate till well after the dinosaurs went extinct.

  2. Interesting! But, our olfactory organs pale in comparison to most other mammals, nay, most other animals. If noses are what got mammals on the up-and-up, how did our primitive sense of smell help us? Or could've have hurt us (i.e. not alerted us to predators, the way noses do for other mammals)? Did we once have large noses, elevating us to the pinnacle of a food web, and then once we'd advanced enough, the sensitivities of our noses were lost in favor of more brain matter rewired for analytical thinking?

    1. I actually have no idea about the variability of noses in the human race, but I do know that the the primate family eschewed a sensitive sense of smell for the wonders of sight. Visual acuity, contrast and motion sensitivity had greater effects in allowing for better adaptation to a variety of environments and for enhancing diet than smell did.

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