Secular trend in human growth can be positive, negative or neutral. Illustrate with examples.

Understanding Secular Trends

Secular trends are not simply individual variations but represent a statistically significant shift in growth parameters over time. They are distinct from ontogenetic growth, which refers to the growth of an individual from birth to maturity. A secular trend reflects changes in the average growth trajectory of a population over multiple generations.

Positive Secular Trends: Increasing Stature

A positive secular trend is characterized by a consistent increase in stature (height) and/or body weight across generations. This is often associated with improved living conditions.

• Dutch Stature Trend: The classic example is the Dutch population, who experienced a significant increase in stature throughout the 20th century. By the 1980s, Dutch men were among the tallest in the world. This is attributed to factors such as improved nutrition (particularly dairy consumption), reduced infectious diseases, and better sanitation. The increase has largely plateaued in recent decades.
• Japanese Stature Trend: Following the Meiji Restoration in the late 19th century, Japan underwent rapid modernization and improvements in diet and healthcare. This resulted in a significant increase in stature, particularly in the post-World War II era. By the 1980s, Japanese men had surpassed many European populations in height.
• South Korean Stature Trend: Similar to Japan, South Korea has experienced a dramatic increase in stature since the Korean War (1950-1953), driven by improved nutrition and socioeconomic conditions.

Negative Secular Trends: Decreasing Stature

A negative secular trend indicates a consistent decrease in stature or body weight over generations. This is often linked to periods of famine, disease outbreaks, or deteriorating living conditions.

• Irish Famine (1845-1849): The Great Famine in Ireland resulted in widespread malnutrition and disease, leading to a decrease in stature among subsequent generations. Studies have shown a reduction in average height in the decades following the famine.
• Soviet Union in the 1930s: Collectivization policies and famines in the Soviet Union during the 1930s, particularly the Holodomor in Ukraine, led to a decline in stature among affected populations.
• Sub-Saharan Africa (some regions): In some regions of Sub-Saharan Africa, persistent poverty, malnutrition, and disease have resulted in slower growth and a lack of positive secular trends in stature. While some progress has been made, challenges remain.

Neutral Secular Trends: Little to No Change

A neutral secular trend signifies a lack of significant change in stature or body weight over generations. This can occur in populations with relatively stable living conditions or those already exhibiting optimal growth parameters.

• Indigenous Amazonian Populations: Some indigenous Amazonian populations have maintained relatively stable stature over time due to their traditional diets and lifestyles, which provide adequate nutrition and physical activity. While data is often limited, observations suggest little to no secular trend.
• Certain Pacific Island Populations: Some Pacific Island populations, with their traditional diets rich in fish and root crops, have demonstrated relatively stable stature over generations, although this can be influenced by changes in diet and lifestyle due to globalization.

Factors Influencing Secular Trends

Several factors contribute to secular trends:

• Nutrition: Adequate and balanced nutrition is crucial for optimal growth.
• Disease: Reduced exposure to infectious diseases allows for better nutrient absorption and growth.
• Socioeconomic Conditions: Improved living standards, access to healthcare, and education contribute to better growth outcomes.
• Genetics: Genetic potential also plays a role in determining growth potential.
• Environmental Factors: Climate and access to resources impact nutritional intake.

Trend	Characteristics	Example	Possible Causes
Positive	Increasing stature/weight	Dutch population (20th century)	Improved nutrition, reduced disease
Negative	Decreasing stature/weight	Irish Famine (19th century)	Famine, disease, poverty
Neutral	Little to no change	Indigenous Amazonian populations	Stable diet, traditional lifestyle

Case Study: The Netherlands – A Detailed Look

The Dutch secular trend in stature is arguably the most well-documented. Starting in the mid-19th century, Dutch men experienced a steady increase in height, peaking in the 1980s at around 183 cm. This was linked to the increased consumption of dairy products, which are rich in calcium and protein. Furthermore, improvements in sanitation and healthcare contributed to reduced childhood mortality and improved overall health. While the growth rate has slowed considerably since the 1980s, the Dutch remain among the tallest populations globally. Research by researchers like Ellemann and colleagues has extensively documented this phenomenon.