Final answer:
The study on MLB players from 1952 found that those with broader smiles lived longer, highlighting how positive emotions may influence longevity. Life expectancy varies due to genetics, lifestyle, and socio-economic factors, and although it has generally increased over time due to advancements in living standards and healthcare, disparities still exist.
Step-by-step explanation:
The question pertains to a study analyzing various characteristics of Major League Baseball players from the 1952 Baseball Register, who had died by 2009, to identify factors associated with longer life expectancy. The correct answer to the question posed is option B, smiles. The research, referred to colloquially as the 'smile study,' found that players with broader smiles in their photos tended to live longer. This finding aligns with broader health research suggesting that positive emotions can have an impact on longevity.
Disparities in life expectancy can be due to numerous factors, including genetics, lifestyle, environment, and access to healthcare. Historically, significant events like the 1918 influenza pandemic and the Great Depression have noticeably influenced lifespan. However, over time, advancements in medical technology and improved standards of living have generally increased average life expectancy. Still, socio-economic factors and race can lead to differences in life expectancy, as seen in the varying statistics between different racial groups.
While factors such as genetic differences and health habits contribute to aging and life span, the specific causes of aging and factors influencing longevity are complex and include both programmed factors, like telomere shortening, and damage-related factors, such as DNA mutations due to environmental stressors.