How Our Three Smallest Bones Led to
Human Brains and Love for Mom
One of the world's leading experts on how humanity came to be, Dr. Melvin Konner,
has recently published a work that has been 25 years in the making: The Evolution of Childhood: Relationships, Emotion, Mind (Belknap Harvard University Press, 2010, 943 pages)
I had the pleasure of knowing Dr. Konner during my time in Boston, and have been studying his book this summer.
From time to time, I would like to post some of his most fascinating findings in this monumental, and historic exploration of how humans came to be.
Today's observation has to do with the emergence of mammals from reptiles and how the mother-child bond helped define our history.
Mammals first appeared on our planet about 225 million years ago, clearly descended from reptiles.
Most people think that to be a mammal you have to nurse your young and/or give birth to a live child, not an egg. Now nearly all mammals do both these things, including humans. But platypuses are mammals and lay eggs, and have no fully developed breasts.
It turns out that the one difference between reptiles and mammals has to do with might appear to be a very minor anatomic detail.
Reptiles have three little bones in their jaw joint. Mammals do not.
Feel your jaw, the jawbone connects directly to your skull. Go ahead, open and close your mouth with your finger on your jaw joint. You can feel the jaw connect directly to your skull. Reptiles have three tiny bones in this joint that act as a major hinge, allowing the reptile to open their mouth far more widely than we can. It explains how a snake can swallow a mongoose- their hinged jaw opens that widely. Ours never will.
So where are the three tiny bones of the reptile jaw in mammals, including us? They have moved inwards, just a few millimeters, and taken their place as the three tiny bones of hearing- the hammer, anvil, and stirrup.
We are not sure what got those bones to move, but the fossil record clearly proves that their movement led to the development of the ear of the mammal, which opened up hearing a much wider range of sounds. With the movement of these, our smallest three bones, the ear of a mammal was born, able to hear high pitches that even today no reptile can hear.
Now you might ask, how does the development of a better ear lead to closer infant-mother connections and the human brain? It turns out, rather directly.
With the advantage of better hearing, the newborn of a mammal can cry out for help in as loud a voice as it wants, the predator reptile cannot hear the baby, but the baby's Mom can. Now, for the first time, a baby can cry out with the predator at the door, without fear of the predator hearing it, and confident the mother will respond.
This new reality ushered in the era of the mammal, and the central fact of mammal life- its babies are deeply connected to their Mamas.
But since hearing became the foundation and starting point for this connection, this move also opened the door to another powerful, and ultimately decisive, advantage for the mammals- the growth of the thinking brain. After all, with the development of better hearing and communication comes the development of language. And many hold that one of the main drivers for the development of the human brain has been language.
So, from the chance movement of the three smallest bones from the jaw to the ear comes a new type of animal, the mammal, the creation of a new type of hearing that leads to a quantum leap in the depth of attachment between newborn and mother, the creation of language, and the direction towards a human brain.
Extraordinary how the random events of evolution can lead to the most extraordinary outcomes!
Dr. Arthur Lavin
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