Characteristics of Life

1. Characteristics of Life • Order • Metabolism • Inheritance • Evolutionary history • Environmental response

2. Microevolution Macroevolution Objectives: To understand: Evolution = Over time, changes occur in: • DNA • Allele frequencies of a population • Traits • A species • Lineages • How biologists think about evolution

3. Change over time = evolution Observations: -Diversity of life has changed on this planet -Changes in form occur in virtually all lineages -Lineages of species are hierarchically related -Competition among close relatives common If change occurs in DNA and allele frequencies, then traits can and do change over time

4. Other mechanisms covered later this week Change happens How might organisms evolve? • Natural selection is one mechanism of evolutionary change • Mutation • Restrictions in gene flow and inbreeding • Random ‘drift’ of traits in small pop’ns

5. Charles Darwin 1809-1882 • He proposed the theory of natural selection • a mechanism that explains change over time • first person to thoroughly document evolution

6. Beliefs in 1800s • Species are fixed in form; species have never changed • Only extinction alters species diversity • Chain of Being • rationale for racism and sexism • Earth is young ~7,000 yrs. old • Catastrophism – • Earth is altered by catastrophes only

7. However, philosophical changes begin in the 1800s. Why? • Democracies arise • status quo challenged • fixity of class and status at birth challenged • Transformism- Lamarck proposes that change occurs; offers a mechanism • Environment can induce traits to change • Traits acquired in organism’s lifetime • Gradual change over generations • are inherited by offspring wrong!

8. Darwin’s life altering experiences: Voyage of the Beagle - 1831-1836

9. Darwin’s thoughts change during voyage • Reads Lyell; gradual changes shape an ancient Earth • Sees catastrophic geologic changes • But, also ponders effects of gradual geologic processes • Sees a vast diversity of life and life forms • Unearths fossil marsupials in S. America • Sees closely related species living in different habitats • Sees island organisms that should be similar to mainland • He deduces that one lineage can produce many different species with specialized traits for specific niches • Sees island species that have ‘lost’ traits • Voyage destroys notion that species are fixed in form • Asks - could time and environment alter species?

10. He also reads: • Malthus • Pop’ns have high capacity for increase • Pop’ns increase faster than food supply • So, starvation and disease limit pop’n size • Smith - competition in free markets results in most fit companies. • Wallace -

11. At home - he practices artificial selection on domesticated animals

12. He proposes a testable hypothesis =Natural Selection • Environment limits pop’n size • Individuals vary (must be genetically based) • Individuals with best traits survive & reproduce • Traits must be heritable • Natural selection results in evolution • Genotypes change over time; adaptations may arise Nature of inheritance clarified by Mendel • Found that traits are predictably inherited • Now we know that traits are affected by the alleles

13. Darwin wrote >20 books, 100s of chapters & essays On the Origin of Species Main points: • The diverse forms of life have arisen by descent with modification from ancestral species • The mechanism of modification has been natural selection working over enormous tracts of time

14. What is antibiotic resistance? How did it evolve? • Antibiotics can kill bacteria (environment limits pop’n size) • Some bacteria resist being killed by antibiotics (individuals vary). • Bacteria have plasmids with antibiotic resistance genes • Resistant bacteria live and reproduce despite antibiotics • Bacteria exchange plasmids during reproduction or absorb gene (traits inherited) • Pop’ns of bacteria begin to have more bacteria that are resistant b/c • resistant bacterialive & reproduce more • A selective advantage and higher fitness exists • Bacteria evolved via natural selection • Why is this common today? • Overuse and inappropriate use of antibiotics provides strong selective pressure

15. Evolution of ‘superbugs’ • Staph and other infections prolong hospital stays In 2000s, 77,000 more people/yr died in US hospitals b/c of infections (relative to early 1990s) ~70% of bacterial infections are resistant to at least one antibiotic • Some infections, TB, malaria, gonnorhea, ear infections becoming very difficult to treatuntreatable • Antibiotic resistant pneumonia bacteria 0.02% 1980  6% • Why? Antibiotics in animal feed, unnecessary & unfinished antibiotic Rxs are causes for evol’n of resistance. • What to do? Don’t ask for antibiotics just b/c you’re sick, complete whole prescription, stay away from hospitals or limit stay, wash hands, protection, prevention

16. Science = development of testable hypotheses; conclusions subject to modification with new data • In science, the word ‘theory’ does not mean speculation. • Theories are repeatedly tested and explanations can change • Science provides details of HOW the universe works. • Evolution has not failed to explain our biological universe • We don’t understand everything and disagreements do exist, but that is how scientific progress is made • If data fails to support evolution, it will be rejected as an explanation • Religion is based on faith; not subject to experimentation • Religions provide us with moral instructions, historical perspectives, and offers explanations of WHY things might be (meaning). Religions encourage us to grow in wisdom & goodness. • Science and religion have the potential to complement one another, to more fully understand and appreciate humanity, the beauty of life, mystery and the universe. • Both expect truth to prevail and wrong to fail. • A deeply religious biologist once stated, “Nothing in biology makes sense except in the light of evolution.” Dobzhansky