Origins and Evolution of Life

Origins of Life

• Chemical evolution preceded biological evolution.
• Chemical reactions formed the first cells, taking about a billion years.
• Biological evolution, from single-celled prokaryotes to eukaryotes to multicellular organisms, has lasted 3.7 billion years.
• Fossil records, ice cores, and DNA analysis provide incomplete knowledge of past life.

Evolution and Adaptation

• Evolution is the change in a population's genetic makeup over time.
• Populations evolve as their genetic makeup becomes different.
• All species descend from ancestral species.
• Microevolution involves small genetic changes within a population over time.
  • Gene pools change via mutations in DNA sequences (passed to offspring).
  • Multiple forms (alleles) of a gene exist.
  • Sexual reproduction randomly recombines alleles.
  • Gene pools consist of all genes in a population's offspring.
    • Mutations introduce genetic variability.
      • Mutations result from external agents (e.g., radiation, chemicals) or random errors.
      • Only mutations in reproductive cells are passed to offspring.
      • Most mutations are neutral; some are detrimental; a few are beneficial.
• Natural selection occurs when beneficial traits, improving survival and reproduction, are passed to offspring.
  • Genetic variability is essential.
  • Traits must be heritable.
  • Differential reproduction occurs, with individuals possessing the trait producing more offspring.
• Adaptations are heritable traits enabling better survival/reproduction in specific environments.
  • Environmental change necessitates adaptation, migration, or extinction.
• Microevolution involves gene mutation, selection of individuals, and population evolution.

Ecological Niches and Adaptations

• An ecological niche encapsulates a species' role in an ecosystem (survival/reproduction considerations).
• Niche includes tolerance ranges, interactions, and roles in matter/energy cycles.
• Habitat is a species' physical location.
• Fundamental niche is the full potential range of conditions; realized niche is the actual part of the potential niche.
• Generalist species have broad niches (tolerate various environments).
• Specialist species have narrow niches (specific environments).
  • Specialist species are vulnerable to environmental changes.
  • Competition can drive divergence of a single species into similar but specialized species.
• Population's gene pool and reproductive rate constrain adaptive potential.
  • Genetically diverse species with rapid reproduction are better able to adapt.
  • Populations reproducing slowly adapt more slowly.
  • Extinction is a possibility when populations fail to adapt.
• Speciation is the origin of new species.
  • Allopatric speciation involves geographic isolation followed by reproductive isolation (so different gene pools no longer combine).
  • Sympatric speciation involves populations living together but diverging due to mutations or behavioral differences .
• Extinction occurs when populations fail to adapt to environmental shifts.

Speciation, Extinction, and Biodiversity

• Natural selection can lead to the development of new species.
• Geographic isolation and reproductive isolation contribute to allopatric speciation.
• Sympatric speciation occurs in populations residing in the same area.
• Extinction arises when populations cannot adapt and results from major environmental changes or introduction of competing species.
• Background extinction rates are normal and gradual.
• Mass extinctions cause large declines in species diversity.

What is the Future of Evolution?

• Artificial selection (breeding for specific traits) is used to alter populations' genetic characteristics.

• Genetic engineering (gene splicing) produces genetically modified organisms (GMOs) and often hastens development (e.g. crops) or creates new medicines.

  • Gene splicing is quicker than traditional crossbreeding.
  • Cloning (replicating DNA) and biopharming use genetically engineered animals.

• Genetic engineering raises ethical, privacy, legal, and environmental concerns.

• Adaptive radiations are periods of rapid species diversification after mass extinction events.

• Human activities are diminishing biodiversity.

• Extinction rates are rising prematurely due to human activity.

• Human behaviors are driven by complex brains and opposable thumbs.