\begin{definition term="Organic evolution"}\textbf{Organic evolution} refers to the gradual changes in the \textbf{structural}, \textbf{behavioral}, and \textbf{functional} traits of living organisms over \textbf{geologic time}.\end{definition}
1. Overproduction and Competition
- Overproduction: Most species produce more offspring than can survive.
- Competition: Limited resources create a \textbf{struggle for survival}.
\begin{callout type="example"}* Peppered Moths: During the Industrial Revolution, \textbf{dark-colored} moths became more common because they were better camouflaged on soot-darkened trees, avoiding predation.
- Antibiotic Resistance: Bacteria resistant to antibiotics survive and reproduce, leading to resistant populations. \end{callout}
2. Variation and Inheritance
- Genetic Variation: Differences in traits arise from:
- Mutations: Random changes in DNA.
- Recombination: New gene combinations during meiosis and fertilization.
- Inheritance: Traits are passed to offspring, ensuring continuity of advantageous traits.
\begin{callout type="note"}Mutations in \textbf{somatic cells} (non-reproductive cells) do not contribute to evolution, as they are not passed to offspring. Only mutations in \textbf{gametes} (sperm and egg cells) are heritable and can influence evolutionary change. \end{callout}
3. Adaptive Advantage
- Individuals with traits that enhance survival and reproduction are more likely to pass on their genes.
- Over time, these traits become more common in the population.
\begin{callout type="example"}* Insecticide Resistance: Insects with genetic resistance to pesticides survive and reproduce, leading to resistant populations.
- Antibiotic Resistance: Bacteria resistant to antibiotics survive and reproduce, leading to resistant populations. \end{callout}
4. Natural Selection
- Natural selection is the process by which \textbf{environmental pressures} favor certain traits over others.
- It acts on existing variation, \textbf{increasing} the frequency of \textbf{beneficial traits}.
\begin{callout type="tip"}When studying natural selection, focus on the \textbf{interaction} between \textbf{genetic variation} and \textbf{environmental pressures}. This relationship is key to understanding how populations evolve over time. \end{callout}
1. Speciation
- Speciation is the formation of new species from existing ones.
- It occurs when populations become \textbf{reproductively isolated} and \textbf{accumulate} enough differences to prevent interbreeding.
Mechanisms of Speciation
- Geographic Isolation: Physical barriers (e.g., mountains, rivers) separate populations.
- Reproductive Isolation: Differences in mating behaviors or timing prevent interbreeding.
\begin{callout type="example"}* Darwin's Finches: Populations on different Galápagos Islands evolved distinct beak shapes due to isolation and adaptation to specific food sources. \end{callout}
2. Gradualism vs. Punctuated Equilibrium
- Gradualism: Evolution occurs slowly and steadily over long periods.
- Punctuated Equilibrium: Long periods of stability are interrupted by short bursts of rapid change, often triggered by environmental shifts.
\begin{callout type="warning"}* Don't confuse \textbf{gradualism} with \textbf{punctuated equilibrium}.
- Gradualism describes slow, continuous change, while punctuated equilibrium involves \textbf{rapid} change during brief periods. \end{callout}
3. Extinction
- Extinction occurs when a species cannot adapt to changing environments.
- It is a natural part of evolution but is accelerated by human activities such as habitat destruction and climate change.
\begin{callout type="example"}* Dinosaur Extinction: Likely caused by a catastrophic asteroid impact, leading to rapid environmental changes.
- Modern Extinctions: Human activities, such as deforestation and pollution, are driving many species to extinction. \end{callout}
1. Fossil Record
- Fossils provide a chronological record of life on Earth, showing transitions between species.
\begin{callout type="example"}* Transitional Fossils: Archaeopteryx bridges the gap between reptiles and birds. \end{callout}
2. Comparative Anatomy
- Homologous Structures: Similar structures in different species, inherited from a common ancestor.
- Vestigial Structures: Reduced or non-functional structures that were functional in ancestors.
\begin{callout type="example"}* Homologous Structures: The forelimbs of humans, whales, and bats share a similar bone structure but serve different functions.
- Vestigial Structures: The human appendix or the pelvic bones in whales. \end{callout}
3. Comparative Embryology
- Early embryonic stages of related species show striking similarities, reflecting shared ancestry.
\begin{callout type="example"}* Vertebrate embryos (e.g., fish, birds, humans) all exhibit pharyngeal slits and a tail during development. \end{callout}
4. Molecular Biology
- DNA and protein comparisons reveal genetic similarities between species.
\begin{callout type="example"}* Humans and chimpanzees share over 98% of their DNA, highlighting their close evolutionary relationship. \end{callout}
1. Mutations
- Definition: Random changes in DNA that create new genetic variants.
- Causes: Errors during DNA replication, exposure to radiation, or chemical mutagens.
- Effects: Most mutations are neutral or harmful, but some provide adaptive advantages.
\begin{callout type="example"}* Sickle Cell Anemia: A mutation in the hemoglobin gene causes sickle-shaped red blood cells. While harmful in homozygous individuals, the mutation provides resistance to malaria in heterozygous individuals. \end{callout}
2. Meiosis and Fertilization
- Meiosis: Produces gametes with unique combinations of alleles through:
- Independent Assortment: Random distribution of homologous chromosomes.
- Crossing Over: Exchange of genetic material between homologous chromosomes.
- Fertilization: Combines genetic material from two parents, creating genetically unique offspring.
\begin{callout type="note"}These processes ensure that each generation has a diverse gene pool, increasing the potential for adaptive traits to arise. \end{callout}
3. Protein Synthesis
- Mutations in DNA can alter protein synthesis, leading to new traits.
- These changes can affect an organism's phenotype and its ability to survive and reproduce.
\begin{callout type="example"}* A mutation in a gene coding for an enzyme might improve its efficiency, providing a metabolic advantage. \end{callout}
- Evolution is a \textbf{unifying} principle in biology, explaining the \textbf{diversity} and \textbf{interconnectedness} of life.
- It highlights the \textbf{dynamic} relationship between organisms and their environments, emphasizing the importance of \textbf{adaptation} and \textbf{survival}.
\begin{callout type="tok"}How does our understanding of evolution influence ethical decisions about conservation? Should we intervene to prevent the extinction of species, or is extinction a natural part of evolution? \end{callout}
\begin{callout type="self_review"}* What are the key mechanisms of evolution, and how do they interact to drive change in populations?
- How do the patterns of evolution, such as gradualism and punctuated equilibrium, differ in their explanations of evolutionary change?
- What evidence supports the theory of evolution, and how do these lines of evidence complement each other? \end{callout}
