September 13, 2006
The Scars of Human Evolution
Alan Mann
Professor of Anthropology Princeton University
Minutes of the First Meeting of the 65th Year
The first meeting of the 65th year of the Old Guard in the Carl Fields Center of Princeton University was called to order by President Joseph Giordmaine at 10:15 AM. The invocation was led by John Marks. Attendance was 96. There was a moment of silence in memory of members who had died during the past year: James Thornton, John McCollough, Gordon Blackeder, Donald Dickason and Behrends “Pete” Messer.
Membership Committee Chair Charles Stenard also announced the names of new emeriti in the present year. They are Ogden Carter, Thomas Huntington, John O’Donoghue, William Pettit, and James Walsh. Certificates will be presented at a future meeting.
Dick Armstrong introduced a guest, the ev. William Barger, retired pastor of the Doylestown PA Presbyterian Church who is moving into the Windrows Community.
Bob Varrin introduced the speaker, Professor Alan Mann of Anthropology at Princeton University, referring to his many teaching awards and his work in forensic anthropology on the origins of language and humanness. He is writing a book on the biological development of the human species which is also the subject of the morning lecture: The Scars of Human Evolution Who Are We? How evolution has shaped our biology – and limited our functions.
Evolution, Dr. Mann stressed, is about change, not necessarily about progress. Anthropology describes modifications in biological structure and function; it does not make historical judgments on them. It isn’t as if, to use his image, our simian ancestors millions of years ago were sitting under a palm tree in Africa asking, “When are we going to evolve into something more successful?” Evolution is not to perfection, but to change in function, and it can lead to new problems as well.
We know that human beings are closest in genetic structure to chimpanzees, with gorillas as more distant cousins. But minor genetic changes can lead to major biological changes, About 5 million years ago such changes took place, we don’t know why, that moved one branch toward bipedalism. These show themselves especially in the spinal column. Chimpanzees are quadrupeds even though they can sometimes awkwardly move on two legs. The curvature of the spine is such that the weight of the body is thrust forward. Dr. Mann illustrated this with a vivid word-picture of chimps trying to carry bananas. With slides he also showed the difference in human structure, with a spine somewhat curved to put all the weight on the hip joint socket and the knee joints below. These in turn have adapted to support this weight. The pelvis has broadened and developed muscles that give stability when weight shifts from one leg to the other, and the knees have shifted structure to direct weight directly down the shinbone to the feet. This enables walking on two feet and frees the hands for moving rocks, carrying daisies or anything else.
All this, however, has led to problems. The speaker concentrated on two.
First, human beings are subject to pains and malfunctions of the discs in the lower back, which are subject to special pressure due to our erect stance and locomotion. The fifth disc above the sacro-iliac joint is especially vulnerable. Two years ago $26 million was spent on back problems, 2.5% of total medical costs. So the very changes that enable us to function bipedally, come with costs, scars of evolution if you will.
These may well have been made worse by our increased body size, more than double in height and weight, our brain size, nearly three times that of our ancestors two million years ago, and our longevity that allows back problems to develop.
The second problem concerns the female body structure and the birth process. The pelvis of a human woman is broader than that of other mammals, strengthened by muscles on the side to support erect body weight and at the same time a uterus and a birth canal. Therefore the angle is greater between hips and knees, which puts more pressure on the knee joints. Women who engage in strenuous running and jumping exercise are twice as likely as men to develop problems in this area. But the main problem is with birth. The birth canal is narrower in humans than in chimpanzees. When the child comes out it presses against greater constriction and its head turns so the mother cannot see it and therefore cannot help with the birthing process. Human beings are the only species we know of that requires the help of someone else to give birth. For centuries this has meant that birth was a more difficult and dangerous process than for other mammals. Even modern medicine has not eliminated this danger.
The large brains of human beings, three times the size they were two million years ago, add to the problem. As an adaptation, a child’s brain develops far less in utero than does that of a chimpanzee. Unlike other mammals human babies are born helpless. Brain size doubles in the first year but during that time a culture of special care has developed to help them survive. Furthermore, even with uterine underdevelopment the human child’s head is large, often creating stress and injury during birth, especially for a young woman whose pelvis is not fully developed. Caesarian sections since 1870 have helped but they are unavailable to millions in the less affluent world. Nor is surgery to repair tears which reach into the anus or the vagina. Millions of women in some parts of the world suffer from these repulsive injuries. Pregnancy in the less developed world is the second leading cause of death in young women. The first is HIV-AIDS. Of course further developments in medical science can help deal with these problems. We might even seek genetic modifications that would deal with the lumbar curve. But then what would happen? In short, human development has been phenomenal, but has also led to terribly difficult, painful and often deadly results. We are survivors. But is this progress? This is for the hearer to decide.
Respectfully submitted,
Charles C. Wes
Membership Committee Chair Charles Stenard also announced the names of new emeriti in the present year. They are Ogden Carter, Thomas Huntington, John O’Donoghue, William Pettit, and James Walsh. Certificates will be presented at a future meeting.
Dick Armstrong introduced a guest, the ev. William Barger, retired pastor of the Doylestown PA Presbyterian Church who is moving into the Windrows Community.
Bob Varrin introduced the speaker, Professor Alan Mann of Anthropology at Princeton University, referring to his many teaching awards and his work in forensic anthropology on the origins of language and humanness. He is writing a book on the biological development of the human species which is also the subject of the morning lecture: The Scars of Human Evolution Who Are We? How evolution has shaped our biology – and limited our functions.
Evolution, Dr. Mann stressed, is about change, not necessarily about progress. Anthropology describes modifications in biological structure and function; it does not make historical judgments on them. It isn’t as if, to use his image, our simian ancestors millions of years ago were sitting under a palm tree in Africa asking, “When are we going to evolve into something more successful?” Evolution is not to perfection, but to change in function, and it can lead to new problems as well.
We know that human beings are closest in genetic structure to chimpanzees, with gorillas as more distant cousins. But minor genetic changes can lead to major biological changes, About 5 million years ago such changes took place, we don’t know why, that moved one branch toward bipedalism. These show themselves especially in the spinal column. Chimpanzees are quadrupeds even though they can sometimes awkwardly move on two legs. The curvature of the spine is such that the weight of the body is thrust forward. Dr. Mann illustrated this with a vivid word-picture of chimps trying to carry bananas. With slides he also showed the difference in human structure, with a spine somewhat curved to put all the weight on the hip joint socket and the knee joints below. These in turn have adapted to support this weight. The pelvis has broadened and developed muscles that give stability when weight shifts from one leg to the other, and the knees have shifted structure to direct weight directly down the shinbone to the feet. This enables walking on two feet and frees the hands for moving rocks, carrying daisies or anything else.
All this, however, has led to problems. The speaker concentrated on two.
First, human beings are subject to pains and malfunctions of the discs in the lower back, which are subject to special pressure due to our erect stance and locomotion. The fifth disc above the sacro-iliac joint is especially vulnerable. Two years ago $26 million was spent on back problems, 2.5% of total medical costs. So the very changes that enable us to function bipedally, come with costs, scars of evolution if you will.
These may well have been made worse by our increased body size, more than double in height and weight, our brain size, nearly three times that of our ancestors two million years ago, and our longevity that allows back problems to develop.
The second problem concerns the female body structure and the birth process. The pelvis of a human woman is broader than that of other mammals, strengthened by muscles on the side to support erect body weight and at the same time a uterus and a birth canal. Therefore the angle is greater between hips and knees, which puts more pressure on the knee joints. Women who engage in strenuous running and jumping exercise are twice as likely as men to develop problems in this area. But the main problem is with birth. The birth canal is narrower in humans than in chimpanzees. When the child comes out it presses against greater constriction and its head turns so the mother cannot see it and therefore cannot help with the birthing process. Human beings are the only species we know of that requires the help of someone else to give birth. For centuries this has meant that birth was a more difficult and dangerous process than for other mammals. Even modern medicine has not eliminated this danger.
The large brains of human beings, three times the size they were two million years ago, add to the problem. As an adaptation, a child’s brain develops far less in utero than does that of a chimpanzee. Unlike other mammals human babies are born helpless. Brain size doubles in the first year but during that time a culture of special care has developed to help them survive. Furthermore, even with uterine underdevelopment the human child’s head is large, often creating stress and injury during birth, especially for a young woman whose pelvis is not fully developed. Caesarian sections since 1870 have helped but they are unavailable to millions in the less affluent world. Nor is surgery to repair tears which reach into the anus or the vagina. Millions of women in some parts of the world suffer from these repulsive injuries. Pregnancy in the less developed world is the second leading cause of death in young women. The first is HIV-AIDS. Of course further developments in medical science can help deal with these problems. We might even seek genetic modifications that would deal with the lumbar curve. But then what would happen? In short, human development has been phenomenal, but has also led to terribly difficult, painful and often deadly results. We are survivors. But is this progress? This is for the hearer to decide.
Respectfully submitted,
Charles C. Wes