Ancient Bones Shed Light on Modern Fractures

MONTREAL — The decreased reliance on brute force and manual labor for human survival during the past few thousand years has taken a toll on bone density, anthropologist Christopher B. Ruff, Ph.D., said at the 17th Scientific Meeting of the International Bone and Mineral Society.

This conclusion comes from a review of archaeological samples of human long bones, reported Dr. Ruff of the center for functional anatomy and evolution, Johns Hopkins University, Baltimore. The modern human genus essentially originated about 2 million years ago. Using cross sections of long bones as a measurement of bone strength reveals that, between 2 million and 8,000 years ago, bone strength relative to body size in humans steadily diminished. Extrapolating the trend to modern times reveals modern humans have bone strength about 30% below what would be expected if the trend had continued. “There are many different possible explanations for this, but my preferred explanation is an environmental one relating to mechanical loading and muscle activity effects,” said Dr. Ruff. Over time but especially in the past few thousand years, modern advances have meant brute force and manual labor are less important for survival. This trend demonstrates how important mechanical loading is for bone strength. The price, of course, is today's increased incidence of osteoporotic fractures.

Archaeological samples also shed light on normal growth and developmental patterns in bone. “Patterns of growth and development are very ancient,” said Dr. Ruff. Computed tomography of the bones of 31 children of various ages who died more than a million years ago reveals a pattern of periosteal expansion, followed, around adolescence, by endosteal expansion and then contraction. Studies of modern tennis players who began practicing the sport at different ages reveal that the same pattern of bone growth persists today.

In addition to revealing these patterns of bone growth, archaeological samples also allow for identifying differences between males and females. For instance, marked endosteal contraction occurs in late adolescence in the female femur but is less apparent in the upper limbs; endosteal contraction occurs equally in upper and lower limbs in men. Both systemic factors, such as hormones, and mechanical factors, such as differences in body size, account for these differences, said Dr. Ruff.

Comparing humans to other species reveals an important difference: Although primates, who use all four limbs for locomotion, have similar bone strength in their upper and lower limbs, bipedal humans have stronger lower limbs than upper limbs. This difference starts to develop after about 1 year of age, because humans are generally quadrupedal in their first year of life. Recognizing this helps archaeologists identify when humans first relied primarily on their lower limbs for locomotion. It also reveals that differences between child and adult skeletons and the growth patterns that lead from one to the other have been maintained for at least 2 million years.

During the past 2 million years, patterns of bone growth and development have remained remarkably stable in humans, allowing for the use of archaeological samples to better understand the bones of modern man. “Archaeological samples tend to be more homogeneous genetically and environmentally, so you get a cleaner signal,” said Dr. Ruff. “They are [from] very similar populations with similar diets, similar activity levels. Skeletal material is available for all ages, as opposed to autopsy samples, where it's very difficult to find younger individuals, and [archaeological samples] can serve as a useful baseline for comparison with really modern samples.”

There are disadvantages to using archaeological samples, however. These include the need to rely on cross-sectional study designs, the potential bias inherent in only being able to study the skeletons that have survived this long, and the inability to reliably determine the sex of the skeletons of humans who died before adolescence or in old age.

MONTREAL — The decreased reliance on brute force and manual labor for human survival during the past few thousand years has taken a toll on bone density, anthropologist Christopher B. Ruff, Ph.D., said at the 17th Scientific Meeting of the International Bone and Mineral Society.

This conclusion comes from a review of archaeological samples of human long bones, reported Dr. Ruff of the center for functional anatomy and evolution, Johns Hopkins University, Baltimore. The modern human genus essentially originated about 2 million years ago. Using cross sections of long bones as a measurement of bone strength reveals that, between 2 million and 8,000 years ago, bone strength relative to body size in humans steadily diminished. Extrapolating the trend to modern times reveals modern humans have bone strength about 30% below what would be expected if the trend had continued. “There are many different possible explanations for this, but my preferred explanation is an environmental one relating to mechanical loading and muscle activity effects,” said Dr. Ruff. Over time but especially in the past few thousand years, modern advances have meant brute force and manual labor are less important for survival. This trend demonstrates how important mechanical loading is for bone strength. The price, of course, is today's increased incidence of osteoporotic fractures.

Archaeological samples also shed light on normal growth and developmental patterns in bone. “Patterns of growth and development are very ancient,” said Dr. Ruff. Computed tomography of the bones of 31 children of various ages who died more than a million years ago reveals a pattern of periosteal expansion, followed, around adolescence, by endosteal expansion and then contraction. Studies of modern tennis players who began practicing the sport at different ages reveal that the same pattern of bone growth persists today.

In addition to revealing these patterns of bone growth, archaeological samples also allow for identifying differences between males and females. For instance, marked endosteal contraction occurs in late adolescence in the female femur but is less apparent in the upper limbs; endosteal contraction occurs equally in upper and lower limbs in men. Both systemic factors, such as hormones, and mechanical factors, such as differences in body size, account for these differences, said Dr. Ruff.

Comparing humans to other species reveals an important difference: Although primates, who use all four limbs for locomotion, have similar bone strength in their upper and lower limbs, bipedal humans have stronger lower limbs than upper limbs. This difference starts to develop after about 1 year of age, because humans are generally quadrupedal in their first year of life. Recognizing this helps archaeologists identify when humans first relied primarily on their lower limbs for locomotion. It also reveals that differences between child and adult skeletons and the growth patterns that lead from one to the other have been maintained for at least 2 million years.

During the past 2 million years, patterns of bone growth and development have remained remarkably stable in humans, allowing for the use of archaeological samples to better understand the bones of modern man. “Archaeological samples tend to be more homogeneous genetically and environmentally, so you get a cleaner signal,” said Dr. Ruff. “They are [from] very similar populations with similar diets, similar activity levels. Skeletal material is available for all ages, as opposed to autopsy samples, where it's very difficult to find younger individuals, and [archaeological samples] can serve as a useful baseline for comparison with really modern samples.”

There are disadvantages to using archaeological samples, however. These include the need to rely on cross-sectional study designs, the potential bias inherent in only being able to study the skeletons that have survived this long, and the inability to reliably determine the sex of the skeletons of humans who died before adolescence or in old age.

MONTREAL — The decreased reliance on brute force and manual labor for human survival during the past few thousand years has taken a toll on bone density, anthropologist Christopher B. Ruff, Ph.D., said at the 17th Scientific Meeting of the International Bone and Mineral Society.

This conclusion comes from a review of archaeological samples of human long bones, reported Dr. Ruff of the center for functional anatomy and evolution, Johns Hopkins University, Baltimore. The modern human genus essentially originated about 2 million years ago. Using cross sections of long bones as a measurement of bone strength reveals that, between 2 million and 8,000 years ago, bone strength relative to body size in humans steadily diminished. Extrapolating the trend to modern times reveals modern humans have bone strength about 30% below what would be expected if the trend had continued. “There are many different possible explanations for this, but my preferred explanation is an environmental one relating to mechanical loading and muscle activity effects,” said Dr. Ruff. Over time but especially in the past few thousand years, modern advances have meant brute force and manual labor are less important for survival. This trend demonstrates how important mechanical loading is for bone strength. The price, of course, is today's increased incidence of osteoporotic fractures.

Archaeological samples also shed light on normal growth and developmental patterns in bone. “Patterns of growth and development are very ancient,” said Dr. Ruff. Computed tomography of the bones of 31 children of various ages who died more than a million years ago reveals a pattern of periosteal expansion, followed, around adolescence, by endosteal expansion and then contraction. Studies of modern tennis players who began practicing the sport at different ages reveal that the same pattern of bone growth persists today.

In addition to revealing these patterns of bone growth, archaeological samples also allow for identifying differences between males and females. For instance, marked endosteal contraction occurs in late adolescence in the female femur but is less apparent in the upper limbs; endosteal contraction occurs equally in upper and lower limbs in men. Both systemic factors, such as hormones, and mechanical factors, such as differences in body size, account for these differences, said Dr. Ruff.

Comparing humans to other species reveals an important difference: Although primates, who use all four limbs for locomotion, have similar bone strength in their upper and lower limbs, bipedal humans have stronger lower limbs than upper limbs. This difference starts to develop after about 1 year of age, because humans are generally quadrupedal in their first year of life. Recognizing this helps archaeologists identify when humans first relied primarily on their lower limbs for locomotion. It also reveals that differences between child and adult skeletons and the growth patterns that lead from one to the other have been maintained for at least 2 million years.

During the past 2 million years, patterns of bone growth and development have remained remarkably stable in humans, allowing for the use of archaeological samples to better understand the bones of modern man. “Archaeological samples tend to be more homogeneous genetically and environmentally, so you get a cleaner signal,” said Dr. Ruff. “They are [from] very similar populations with similar diets, similar activity levels. Skeletal material is available for all ages, as opposed to autopsy samples, where it's very difficult to find younger individuals, and [archaeological samples] can serve as a useful baseline for comparison with really modern samples.”

There are disadvantages to using archaeological samples, however. These include the need to rely on cross-sectional study designs, the potential bias inherent in only being able to study the skeletons that have survived this long, and the inability to reliably determine the sex of the skeletons of humans who died before adolescence or in old age.