Evolution of Ideas: Darwin's Theory

The Evolution of an Idea

• Darwin's theory of evolution is based on the idea of natural selection
• This theory proposes that advantageous traits become more common within a population over generations
• Traits are hereditary, meaning that they are passed from parents to offspring
• Organisms in a population vary in traits, some are better suited to survive and reproduce in a specific environment than others
• The environment has an impact on the usefulness of a trait
• Gradual changes in heritable traits (genes) occur in populations from one generation to the next
• Individual organisms do not evolve, populations evolve

Changes between Generations

• Evolutionary adaptation occurs when a mutation is favored by the environment
• The mutation creates a 'new' trait
• A new trait could be harmful, neutral, or favorable to the individual in a given environment
• A harmful trait could cause the loss of that trait(gene pool). This loss occurs because the individuals with the trait are less likely to survive and reproduce, leading to a reduction in the frequency (number) of the trait in the population.
• A neutral trait will have a low frequency in a population because, while it does not negatively impact survival or reproduction, it does not provide an advantage. This means that individuals with the trait have a similar chance to other individuals in the population to survive and reproduce.
• A favorable trait could cause of that trait in the population because these individuals will be more likely to survive and reproduce, leading to an increase in their frequency (number)

Mutations and the Environment

• The effect of a mutation depends on the environment
• The same mutation can be harmful in one environment, neutral in another, and beneficial in a third
• Mutations can be harmful if exposed to a toxin or chemical in an environment.
• Mutations can be beneficial when a species is exposed to an advantage that helps its survival or reproduction. Examples include opposable thumbs, binocular vision.

What is Evolution?

• Evolution is the gradual change in inherited traits within a population of organisms over the course of generations.

How do organisms evolve?

• Populations evolve, not individual organisms.

Genes

• DNA contains genes which code for building organisms in a specific way.
• Genes are passed from parent to offspring

Darwin & Natural Selection

• Darwin developed the theory of natural selection
• A process in which organisms best adapted to their environment are most likely to survive. This ultimately leads to more viable species in a given time/environment.

The Voyage of the HMS Beagle

• Darwin served as a naturalist on the HMS Beagle
• The voyage lasted from 1831-1836
• Darwin observed plants, animals and fossils
• Darwin studied South America and the Galapagos Islands

Theory of Evolution by Natural Selection

• Over time, populations change in advantageous traits as those traits become more common after generations.
• Individuals in a population compete for resources, resulting in a population difference
• More offspring are produced than can survive
• Food and resources are often limited
• Some individuals inherit traits giving them a survival/reproductive advantage
• Many inherited traits (variations) are passed on via reproduction

Natural Selection

• Natural selection occurs due to interactions between the environment and the genetic makeup of individuals within a species
• Natural selection leads to differential success in reproduction among individuals, meaning some organisms have a better ability to survive and reproduce than others
• Populations of organisms adapt to their environment through natural selection

Theory of Natural Selection

• Heritable favorable traits amongst individuals create a better adaptation in their population to their environment.
• Darwin's Galapagos finches display diversity in bill size and shape, each adapted to a specific food source.

Evolution of Antibiotic Resistance in Bacteria

• Antibiotic resistance evolves due to natural selection similar to resistance of insects to pesticides
• Antibiotic use creates selection among bacteria, ensuring only resistant individuals survive
• Resistant bacteria reproduce rapidly, becoming more common in a population; this is faster than the non-resistant bacteria

Helpful Terms

• Adaptation: a structural, behavioral, or biological process that helps an organism survive within a specific environment
• Mimicry: an example of a structural adaptation that helps a harmless organism resemble a harmful organism
• Vestigial structure: a structure/trait that once had a function in a prior ancestor but has lost its purpose over time.

Practice Questions

• Variation and selection are necessary elements of Darwinian evolution
• Differences in trait result in members of a population being selected
• Predatory cats haven't evolved to be as fast as cheetahs due to different ecological niches.
• Natural selection favors different sizes in different species (elephants/mice) as it's a factor in their survival and reproduction in a niche.
• Hair is not considered a vestigial trait in humans.

Explore the foundations of Darwin's theory of evolution focusing on natural selection and the hereditary nature of traits. This quiz will guide you through the concepts of evolution, adaptation, and the role of the environment in shaping populations over generations.