Evolutionary Theory Notes
Evolutionary Theory
Evolution involves populations changing over time, with new species arising from ancestral ones. This wasn't immediately obvious, but observations led Charles Darwin and others to propose this idea. Understanding these observations is crucial for discussing species progression or explaining population differences.
Mechanisms Causing Population Change
Five Key Observations:
Exponential Fertility:
All organisms can produce many offspring, far exceeding what's needed to maintain the population.
Example: Dandelions
Each flower head has ~100 seeds.
A healthy plant has 40-50 flower heads per season.
One plant can potentially produce new plants.
Each of those 50,000 plants can produce another 50,000 plants each.
Humans: Although not as rapid as dandelions, humans also possess the capacity for exponential population growth.
Consider a female starting at age 16, with a 10-month gestation period i.e. 40 weeks.
Population Stability and Resource Limitation
Exponential Fertility vs. Stable Population Size
Despite the potential for exponential population growth due to high fertility rates, populations tend to remain relatively stable.
Populations do not explode to fulfill their full reproductive capacity.
Limited Resources
Limited resources are key factors that constrain population growth.
Three main categories of resources:
Food (including water)
Space
Access to reproduction
These resources are not unlimited, impacting organism survival and reproduction.
Individual Variation
Individuals within a species are not identical; variation exists among them.
"All men are not created equal" - While a notable political statement, it does not reflect biological reality.
Variation is a fundamental aspect of biological populations.
Heritability of Variation
A significant portion of the variation observed in organisms is heritable.
Traits and characteristics can be passed down from parents to offspring.