Humans do not have a fixed lifespan of 100 years; in fact, the human lifespan can vary significantly from one individual to another. While the average life expectancy at birth in many countries is around 70 to 80 years, many people live well beyond 100 years, and there is considerable variation in lifespans due to various factors. Here are some reasons why humans do not have a fixed lifespan of 100 years:

1. Genetics: Genetic factors play a significant role in determining an individual’s potential lifespan. Some people inherit genes associated with longevity, while others may inherit genes that predispose them to certain health conditions that can affect their lifespan.
2. Environmental Factors: Environmental factors, such as diet, exercise, access to healthcare, and exposure to toxins, can greatly influence how long a person lives. A healthy lifestyle can contribute to a longer life.
3. Medical Advances: Advances in medical science, healthcare, and disease management have increased human life expectancy over the years. Medical interventions, such as vaccines, antibiotics, and improved surgical techniques, have reduced mortality from various diseases.
4. Nutrition: Access to a balanced and nutritious diet can have a profound impact on health and longevity. Proper nutrition can help prevent or manage chronic diseases and support overall well-being.
5. Social and Economic Factors: Socioeconomic factors, including income, education, and living conditions, can affect health and access to healthcare services. People in more privileged socio-economic situations often have better health outcomes.
6. Lifestyle Choices: Choices related to smoking, alcohol consumption, physical activity, and stress management can significantly influence a person’s health and lifespan.
7. Genetic Diversity: Human genetic diversity is vast, and some populations have exhibited longer lifespans than others due to a combination of genetic and environmental factors.
8. Advancements in Healthcare: Ongoing advancements in healthcare, such as personalized medicine and treatments for specific health conditions, can further extend human lifespans.

While humans have made substantial progress in extending the average lifespan, there is no set limit to how long an individual can live. As our understanding of genetics and health continues to advance, it is possible that future generations may experience even longer lifespans. Ultimately, the human lifespan is influenced by a complex interplay of genetic, environmental, and lifestyle factors, and it is not fixed at 100 years.