Natural Selection and Tuberculosis Overview

Overview of Natural Selection

• Natural Selection: Primary mechanism of evolution.
• Other factors affecting evolution include genetic drift, which occurs by chance.

Tuberculosis (TB)

• Causative Agent: Mycobacterium tuberculosis.
• History: Emerged around 70,000 years ago, expanded during the Neolithic period.
• Impact: Killed 1 in 5 adults in Europe and North America (17th - 19th centuries).
  • Currently, 2 billion people are carriers.
  • New infections occur at a rate of 1 per second.
  • Causes approximately 2 million deaths yearly.

Early Treatment of TB

• 19th - early 20th century treatments involved sanatoriums.
• Contracting TB was often seen as a “death sentence.”

Antibiotic Revolution

• Discovery of antibiotics transformed TB treatment:
  • Isoniazid (1952)
  • Ethambutol (1961)
  • Rifampin (1966)
  • Pyrazinamide (1952)

Antibiotic Resistance

• Resistance has been observed since the 1980s, increasing global TB cases:
  • Multi-drug resistant TB (MDR-TB): 20% of cases resistant to first-line drugs.
  • Extensively drug-resistant TB (XDR-TB): 2% of cases resistant to second-line treatments.
  • 1/3 of those with XDR-TB die from the disease.

Incidence Trends

• Current trends show increasing TB cases, rivaling AIDS as a leading infectious cause of death globally.

Mechanisms of Natural Selection

1. Variation: Individuals within populations exhibit variations.

   • Applies to both human and non-human populations (includes traits like blooming time).

2. Heritability: Variations can be passed on to offspring.

   • Example: Animal breeders enhance traits through selective breeding.

3. Overproduction: Populations produce more offspring than can survive.

4. Survival and Reproduction: Not random; based on fitness and adaptation.

   • Fitness: Relative survival and reproduction of individuals.
   • Adaptation: Traits that enhance fitness in specific environments.

Effects of Natural Selection

• Natural selection drives adaptation to environments, affecting population traits over generations.
  • Not all adaptations derive perfection; what is beneficial in one context may be detrimental in another.
  • Selection operates on existing variations, not generating new traits.

Artificial Selection

• Imposed by human choice (e.g., livestock and dog breeds).
  • Example: Dachshunds bred for short legs demonstrate artificial selection.

Misconceptions about Natural Selection

• Natural selection does not result in progression towards a goal or organismal perfection.
  • Organisms are the fittest for current environments, but not inherently better overall.
  • Humans cannot choose evolutionary changes for organisms.

Laboratory Studies of Natural Selection

• Example: Studies on alcohol metabolism in fruit flies demonstrate existing population variations.

Summary of Natural Selection Effects

• Favorable inherited variations increase in frequency.
• Unfavorable variations are lost, resulting in changes in population traits over generations.