Describe the concept of natural selection. Give some examples.
http://evolution.berkeley.edu/evolibrary/article/evo_25
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/bio%20101%20lectures/Natural%20Selection/natural.htm
http://en.wikipedia.org/wiki/Natural_selection
The concept of natural selection is a fundamental principle in evolutionary biology. It was first proposed by Charles Darwin, who described it as the mechanism by which species evolve and adapt to their changing environment over time. Natural selection is the process through which certain traits or characteristics become more or less common in a population based on their impact on an organism's ability to survive and reproduce.
Here's a step-by-step breakdown of the concept:
1. Variation: Within a population, individuals display a wide range of genetic and phenotypic variation. This variation can arise through genetic mutations, genetic recombination, or gene flow from other populations.
2. Overproduction: Most species produce more offspring than can survive to reproductive age. This leads to competition among individuals for limited resources such as food, water, and mates.
3. Selection pressure: The environment presents challenges or pressures that impact an organism's survival and reproductive success. These pressures can include predation, disease, habitat conditions, or changes in food availability.
4. Differential survival and reproduction: Individuals with traits that are better suited to their environment are more likely to survive and reproduce. This creates a differential reproductive success, where individuals with advantageous traits are more likely to pass on their genes to the next generation.
5. Inheritance: The advantageous traits are typically heritable, meaning they can be passed down to offspring through genetic inheritance. This leads to an increased prevalence of these traits in the population over time.
Examples of natural selection can be observed in various organisms and environments:
1. Peppered Moths: Before the industrial revolution, peppered moths in England predominantly had light-colored wings, which helped them blend in with tree bark and avoid predation. However, as industrial pollution darkened the trees, darker-winged moths became better camouflaged and had higher survival rates, leading to an increase in their population.
2. Antibiotic resistance in bacteria: In the presence of antibiotics, bacteria that have acquired a genetic mutation or acquired resistance genes are more likely to survive and reproduce. Over time, the population becomes dominated by resistant bacteria, leading to the development of antibiotic-resistant strains.
3. Darwin's Finches: The finches in the Galapagos Islands have evolved different beak sizes and shapes to suit their respective food sources. Some finches have adapted to eat tough nuts, while others have developed beaks that allow them to feed on insects or nectar. The beak variations confer specific advantages in obtaining food, leading to the survival and reproduction of the individuals with the most suitable beak shape for their environment.
These examples illustrate how natural selection acts as a driving force in evolution, favoring the survival and propagation of traits that enhance an organism's fitness in a given environment. By understanding natural selection, we can better comprehend how species diversify and adapt to changing conditions.