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On Mother's Day 2), it's customary * to speak about the sacrifices our mothers made to improve our lives. But mothers also deserve credit for the pivotal role they've played in the story of human evolution. Prehistoric mothers did nothing less than seed the development of our species' remarkable intelligence.
The story begins at least two million years ago, when our brains started to grow larger, eventually making humans the most cognitively advanced species on earth. This evolution was not without its difficulties, particularly for mothers. That's because, some five million to seven million years ago, soon after the human lineage branched * from the ancestors of chimpanzees, another peculiarity increasingly came * to mark our progenitors *: walking upright on two legs, or bipedalism *.
The evolution of bipedalism gradually altered our ancestors' skeletons. By the time brain size began trending upward, the shape of the human pelvis had changed to accommodate the muscle attachments that facilitated * walking (and running) in a more vertical posture. As a result, parts of the birth canal narrowed, making the passage of big-brained infants increasingly difficult.
The combination of big brains and constricted * birth canals was an obstetrical problem * for early mothers and no doubt led to high rates of maternal and infant mortality. The infants who survived were the ones whose heads were small enough to squeeze through * narrowed birth canals, but to thrive outside the womb, human development favored * big brains. And so natural selection 3) encouraged the early birth of human fetuses, before they had finished gestating *. For that reason, our babies are born in immature, helpless states compared with those of the apes.
Had it not been for the natural selection of enlarged brains, our species would have evolved in a completely different direction. There would be no theory of relativity, no knowledge of "entangled" particles or the human genome 4); we'd have no great art, music or novels. The excruciating * pain and trauma of childbirth are the cost our species has paid for its fancy cognition. And mothers continue to pay the debt.
But that's hardly all prehistoric mothers gave us. They also may well have touched off * the evolution of language from the sounds they made to reassure their helpless infants. Baby chimpanzees, after all, can cling to their mothers' hairy chests and contentedly ride along, nursing * on demand. But human infants, born immature, lack that dexterity. Before the advent of devices like baby slings, the burden of carrying helpless infants presented a quandary * for early mothers as they foraged for food and water.
To accomplish their tasks, ancestral moms would at times have needed to put their babies down, and these interruptions in physical contact would have been as distressing for infants then as they are now. It's very likely that mothers began to use special vocalizations to reassure and quiet their infants. These vocalizations were the origin of the more complicated lullabies and baby talk, sometimes called "motherese *," that exist today in nearly all human cultures, but which are totally absent among chimpanzees.
Motherese helps infants learn the rhythms and rules of their native speech through simple vocabulary, extensive repetition, exaggerated vowels, high tones and slow tempo. The road from mothers' reassuring vocalizations to the first speech would have been a long one, but these interactions between prehistoric mothers and infants may very well have paved the way for the emergence of spoken words.
Many linguists think that the first human language was very simple and probably consisted mostly of nouns. But to what would the first words have referred? Kin, foods, predators, tools and weather have all been suggested.
I suspect that one of the first words invented was the equivalent of "Mama." Surely, maturing infants, then as now, would have sought a name for the being who provided their first experiences of warmth, love and reassuring melody.
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