Evolution Notes

Evidence, Causes, and Patterns of Evolution

Evidence of Evolution

• The Fossil Record
• Geographic Distribution of Living Things
• Comparative Anatomy
• Similarities in Embryology
• Biochemistry

The Fossil Record

• Layers in Earth’s crust show change over time.
• The deeper the fossil, the older it is.
• We can compare old and new fossils to observe changes.

Dating Fossils

• Relative Dating: Fossils found in lower layers of rock are older than those found near the surface.
• Radiometric Dating (Numerical Dating): Comparison of radioactive and non-radioactive elements in a rock can predict the age of the rock and the fossil within it.
  • This often involves dating volcanic ash layers surrounding the fossil.

Geographic Distribution of Living Things

• Organisms that live in similar environments often have similar characteristics, even if they are geographically far apart.

Comparative Anatomy

• Homologous Structures: Anatomically similar structures inherited from a common ancestor.
• Analogous Structures: Structures that are anatomically different but serve the same purpose; these come from different ancestors.
• Vestigial Organs: Organs that do not serve a purpose and are lost through evolution and mutation (e.g., appendix, tailbone).

Homologous Structures

• An organ or bone found in different animals supports the idea that different animals descended from a common ancestor and serves as evidence of evolution.

Vestigial Structures

• Features of a species that have no apparent function and appear to be leftover parts from a past ancestor. Examples: wisdom teeth, goosebumps, appendix.

Analogous Structures

• Features of different species that are similar in function but not in structure and do not stem from a common ancestral feature. Example: wings of an insect, bird, & bat.

Comparative Embryology

• Embryos of different organisms are similar, indicating a common ancestor.

Biochemistry (DNA)

• The closer the evolutionary relationship between organisms, the more alike the structure of their DNA and protein molecules.

Causes of Evolution

• If alleles in a population remain the same, evolution will remain at EQUILIBRIUM; meaning no change occurs.
• Disruptions of Equilibrium:
  • Mutations: Changes in DNA can lead to variation.
  • Natural Selection: Changes in the environment cause certain traits to be more favorable.
  • Random Mating: Mating outside of the population can introduce new alleles.
  • Genetic Drift: Random change in allele frequencies.
  • Gene Flow: The movement of genes between populations.

Genetic Drift

• Change in allele frequency due to chance.
• Founder Effect: A small group of organisms settles in an area separated from the main population.
  • Example: Amish people, who have a limited gene pool due to their isolated communities.
• Bottleneck Effect: A population declines significantly in size, then rebounds.
  • Example: Northern Elephant Seals, whose population decreased significantly due to hunting, resulting in less genetic variation in the current population.

Founder Effect Example

• A few individuals from a population start a new population with a different allele frequency than the original population, often on an isolated island.

Bottleneck Effect Example

• A parent population experiences a drastic reduction in the number of individuals due to a bottleneck event, leading to a surviving population with reduced genetic diversity, which is then passed on to the next generation.

Gene Flow

• Genes/traits in a population remain the same until new organisms enter or leave the population, altering the allele frequencies.

Patterns of Evolution

• Adaptive Radiation/Divergent Evolution:
  • Species diverge from a single ancestor, usually due to different environments.
• Coevolution:
  • Species evolve in close relationship with other species.
• Convergent Evolution:
  • Unrelated species evolve to form similar adaptations due to living in similar environments.

Divergent Evolution

• Shows how species can have common (homologous) anatomical structures that have evolved for different purposes.
• Species appearance becomes more different over time.
• Species are closely related genetically.

Convergent Evolution

• Shows how species have evolved separately but have similar (analogous) structures.
• Species appearance becomes more similar over time.
• Species are unrelated (genetically different).

Evolution Fun Facts

• The species Homo sapiens is still evolving rapidly.
• Homo sapiens has only had a culture for less than 50,000 years.
• Humans have incredibly low genetic diversity.
• We share 99.9% of our DNA with other humans, 98.8% of our DNA is similar to chimpanzees, and we share 70% of our DNA with a slug.