by Roger Bourke White Jr., May 1994
Homo sapiens is earth's most intensive language user. Homo sapiens also has a long life compared to the species' body weight, and Homo sapiens women are one of few female mammals that survive long after menopause. Are these related? Yes, language use makes long life a survival aid, and researching life span may provide a clue as to when the human species developed strong language skills.
Shrews live one or two years, then die of old age. Elephants live about one hundred years. Cats and dogs live about 10 and 15 years respectively. If you draw a graph comparing mammal body size to mammal life span, there is a correlation -- the larger the body, the longer the life span.
This trend is so distinct that there is probably a good engineering reason behind it. There must be a design constraint of some sort that makes long life difficult to sustain in mammals, and so evolution trades off benefits in other areas to lengthen the life span of a species' members. Paying for longer life by taking away from some other capability, such as running faster, makes sense when the species has invested a lot in individual members of the species. Large size is a large investment, so it pays to have larger animals live longer, and thus we see the correlation between size and life span.
Homo sapiens is off the normal weight-life span curve. Humans live too long for their size. Humans fall in size between dogs and horses, so they should live about 20 years, not 80. If humans are paying for this long life by trading off some other capability, then something about the design of humans has made long life much more valuable to humans than it is to the average mammal. It isn't size, so it must be something else.
It could be there is something about the human body that is considerably more complicated than the design used in the average mammal of human size. The complexity of the human brain could make growing one a considerable investment, and thus make a longer life optimal for the human design.
Or, long life could improve human survivability more directly. Long life may take advantage of a specific human capability that other comparable-sized animals don't have: Rich language capability, which allows humans to move complex ideas from one species member to another.
Strong language skill allows one member of a species to pass complex information to another. Without language, communicating a complex direction can be done only with the "follow me" command, and warnings can be little more than, “Look out!"
With language, direction giving can be complex, and warnings can be a million times more detailed.
Long life becomes valuable because an older generation can teach a younger generation a million-fold more things. Take the message, “Son, there's a drought this year on the desert. I went through a similar time twenty years ago. The mid-desert springs won't have enough water for the whole tribe. The tribe will have to split and regroup at the river on the far side."
This kind of message is a tribe-saver, but available only to a long-lived species with language. Language and long life are synergistic capabilities.
Language can also have another influence on evolution: A parent can tell an offspring whom to marry. Language allows arranged marriage. Without language, a male must look suitable only to the female he is courting, and vice versa. With language comes arranged marriage, and a male must look suitable to both the female and her family, and vice versa.
Language strongly promotes long life, so the fossil record should show increases in the average age of humans and human predecessors as language skill strengthens. Longer-lived species members should be a sign of language progression.
Parental selection of a mate should change the selection criteria slightly. Desirable characteristics -- those that are selected for when a mate is picked -- should be slightly different when the scrutinizer is a father or mother, so there should be a change in how the species is evolving. This is a subtler change, but perhaps it too can be a sign in the fossil record indicating when language developed. One indicator related to mate selection would be signs of marriage ceremonies.
Strong language use is one of the decisive differences between Homo sapiens and other species on Earth. Language ability will not appear in isolation. It will change the optimal design of the human body, so many other changes in the body will take place at the same time. Some of these changes, such as long life, should be observable in the fossil record, and from this, we can determine when extensive language use evolved in humans.
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