Shortness, reduced mobility and sore joints may not come to mind when

Shortness, reduced mobility and sore joints may not come to mind when you think of survival of the fittest. But human evolution could suggest otherwise. In a new study, researchers found that as early humans migrated into colder northern climates, a genetic mutation that knocks about a centimeter off height and increases the risk of osteoarthritis by up to 80 percent may have helped some of them survive the most recent ice age. While some traits resulting from this mutation may seem unfavorable today, they were advantageous to early humans venturing out of Africa about 60,000 years ago. “There are many cases like this where evolution is a trade-off,” said David Kingsley, an author of the study, which appeared in Nature Genetics on Monday, and a professor of developmental biology at Stanford University.

The shorter stature may have helped these prehistoric humans retain heat and stave off frostbite in their extremities, the authors said. It also may have reduced their risk of life-threatening bone fractures when slipping on icy surfaces. But the same gene puts humans at greater risk for arthritis in the modern era as they live well beyond their reproductive years. The study looked at variants of the GDF5 gene, which was first linked to skeletal growth in the early 1990s, and is known to be involved in bone growth and joint formation. The researchers wanted to understand how the DNA sequences around it might affect the gene’s expression, focusing on one region they named GROW1.

After analyzing the sequence of GROW1 in the 1000 Genomes Project database, a collection of sequences from human populations around the globe, the researchers identified a change in one nucleotide, the basic building block of DNA. The change is prevalent in Europeans and Asians but rare in Africans. To see if that mutation was incidental or actually caused shorter stature, they tested the nucleotide change in mice and found it decreased the length of their long bones, much as it is thought to do in humans. That mutation of the regulatory region analyzed in the study is present in more than 50 percent of the population in Europe and Asia. In some Asian populations, it’s up to 90 percent, Dr. Kingsley said. Even if the variant plays only a small role in increasing arthritis risk, the sheer number of people who possess it means it can have a significant effect. “The very abundance of the change means it could contribute to a lot of cases of arthritis,” Dr. Kingsley said.

A similar evolutionary paradox can be seen with sickle cell anemia, a condition in which a low number of red blood cells makes it difficult to carry adequate oxygen throughout the body, Dr. Kingsley said. A genetic variant causes a high rate of the disease in African populations. But that variant was favored because it also confers protection against malaria. “The genome is complex and our evolutionary history is complex,” said Terence D. Capellini, one of the lead authors on the study and an associate professor in the department of human evolutionary biology at Harvard University. “Because of that complexity, relationships emerge between different aspects of our biology that may seem paradoxical. As we reveal this history of our genome and how it affects our biology, we begin to understand the connections.”

As with many aspects of evolutionary research, it’s easier to figure out what traits were favored than it is to explain why. While shorter stature may have been a protection against the cold and icy terrain, it’s hard to be certain, said George Perry, associate professor of anthropology and biology at Pennsylvania State University, who is not affiliated with the study. “We’re not going to know that without some combination of a time machine and an experiment we can’t do,” he said. But detailed studies like this can help further our understanding of complex evolutionary processes and the potential consequences for modern medicine and human health, Dr. Perry said.

1. Which evolutionary paradox has the author touched upon in the passage?

A. The higher the number of red blood cells, the higher is the protection against malaria.
B. A genetic mutation that provided protection against the cold and fractures in the past now enhances the risk of osteoporosis and arthritis.
C. The very abundance of genomes contributes to increasing the risk of osteoarthritis.
D. Less oxygen throughout the body will lead to a decrease in immunity against malaria.
E. None of these

2. Which of the following can possibly be one of the many cases where evolution is a trade-off?

A. Sacrificing a few hours of sleep so we can get up early in the morning and work on our fitness.
B. Prescription of hormone replacement therapy to post-menopausal women – while it may reduce the risk of ovarian cancer, it will reduce the risk of breast cancer.
C. While higher birth weight provides a higher chance of survival in the first few weeks after birth, babies that are too large have higher susceptibility to airborne infections.
D. Certain variants of a gene called APOL1 either make people resistant to trypanosomal infections or increase the risk of kidney failure.
E. None of these

3. Which of the following statements correctly highlights the impact of shorter stature on modern humans as can be inferred from the passage?

A. Shorter stature can protect humans against the risk of osteoporosis and arthritis.
B. Shorter stature can help in reducing the risk of life-threatening bone fractures.
C. Shorter stature can be a hindrance to fitness.
D. Can not be inferred.
E. Can be inferred but none of the options provided here.

4. Which of the following statements is consistent with the information given in the passage

A. Generally, Europeans and Asians are shorter than Africans.
B. GROW1 is responsible for causing shorter stature.
C. The growth region GROW1 is endogenous to the GDF5 gene.
D. The mutation in the GDF5 gene is one of the main reasons as to why arthritis is prevalent among Asians and Europeans.
E. None of these

5. Which the following statements about the evolutionary studies mentioned in the passage is true?

A. There is a foolproof method to conclude the findings of the study in question.
B. The studies may help in shaping up modern health care.
C. Explaining why certain traits are favorable is more difficult than figuring out what those traits are.
D. The studies are full of paradoxes which make them more complex to understand.
E. None of these

6. Which of the following can be inferred from the passage?

A. People who have arthritis tend to survive extreme conditions better than those who don't.
B. At one point of time, all the humans on Earth belonged to Africa.
C. The genetic mutation that makes people shorter is the reason why early humans survived the most recent ice age.
D. The traits that our ancestors found to be advantageous are the same traits that we find to be disadvantageous.
E. None of these