It is obvious that US citizens, as well as other nations, have became taller within recent 100 years. Though, according to scientists of Tennessee university, that is not the only change. The scientists lead by Richard Jantz started their work as an attempt to perfect the skeletons dating method, though later it turned into a big investigation of how people had changed during several generations. In the 1980s, anthropologist Richard Jantz tried to study this question, while hoping to make easy the work of forensic medical experts. In particular, he compared skeletons belonging to people of 20th and of 19th centuries. Human skeletons are often found in forests by hunters and travellers, some people even decorate their flats with human skulls found in cemeteries or even stolen there. These skulls often turn out to belong to first American settlers or to Indians. Skeletons that got to the scientists hands were compared with data of the national forensic information base created about 15 years ago. Afterwards, the results were united and added with results of anthropological investigation carried out by Mildred Trotter during World War II. It is well known, that within 20th century Americans became several centimetres taller, though it is not the only change that happened. Skeletons of today’s Americans seriously differ from their 19th century ancestors’ skeletons. Today’s Americans are less capable to withstand to serious physical loads. These changes could be seen in the form and length of legs and forearms’ bones. According to the scientists, today’s Americans possess a smaller bone mass than their ancestors, while these changes are so noticeable, that it is easy to determine to what century the skeleton belongs to 20th or to 19th. Today’s people have lost bones’ solidity peculiar to their ancestors. There are many theories explaining the reasons of these changes. The most probable explanation is combination of a better nutrition and a smaller quantity of physical exercises, which causes fundamental biological changes. In 19th century, people ate enough, while today’s people eat well and too much, so up-to-date issue is over-eating, but not starvation. Therefore, people grow faster and sooner reach puberty, in other words, people mature in some other way. Some changes in skeleton’s structure could be explained also with a less level of physical activity. Human bones simply do not develop as strongly, as 100 years ago, when physical exercises stimulated their growth. Ancestors of today’s Americans had a more active life style. They had almost always to go on foot, while today’s people have to make additional efforts for a more physically active life. What is also very important is that in 20th century, children’s death-rate seriously reduced, as a result, many people who could have died in their childhood became adults and even have their own children. Richard Jantz is intending to compare the results with results of investigations carried out other countries, though he is afraid it could be impossible because of some cultural differences. Special attention of the scientists is paid to countries that became fields of bloody conflicts.