19th Century Scientists

In the early 1800s, there was no conflict between science and religion
Creationism was based on the bible and that organisms were created in the form they are currently seen as
Scientists explored and found conflicts with the bible

Naturalist
Sailed on H.M.S. Beagle
Initially supported creationism
Observed plants and animals on Galapagos islands
Different finch species on different islands
- Ate different foods and beaks allowed easy access to foods
- Beaks develop depending on island conditions
Proposed evolution
- Organisms change over time as they adapt to a changing environment
Made 3 assumptions
- Environment is not static, but ever-changing
- Change is slow but continuous
- Change results in different characteristics for organisms
Evolution via natural selection
- Organisms that adapt to a changing environment can survive and reproduce
3 components to this natural selection…
- Variability
  - Members of a species vary along certain characteristics
- Competition
  - More offspring that the environment can handle
  - Members compete for limited resources
- Heritability
  - Members that reproduce will pass on adaptive characteristics
Do animals inform about human behaviors?
Comparative Psychology
- Study of psychology dealing with comparisons of different species
Inspired Francis Galton

How did adaptive characteristics get passed down?
Mendel used pea plants to discover what genes were
- Mechanism for passing on characteristics

Amateur scientist who was Darwin’s cousin
Explorer
Studied how human characteristics adapt to different environments
Measure individual differences such as…
- Height
- Weight
- Physical attractiveness
- Intelligence
Made many discoveries
- Impacts of human heredity
- Nature vs Nurture
- Developed mental tests
- Daily weather reports
- Used fingerprints
Eugenics
- Improving human condition through genetic control
Advocated for positive eugenics
- Use of government money to have intelligent people have children
Negative eugenics
- Eliminate undesirable people from the population
Justified discrimination in education and employment, alongside the sterilization of developmentally disabled individuals
Introduced nature vs nurture
- Nature is a person’s genetic inheritance
- Nurture is the environmental conditions
- Used identical twins to study how genes or environment influence behavior
How did he collect and analyze data?
- Questionnaires
- Normal Distributions
  - Most data points cluster around mean
  - Many human traits conform to normal distribution
- Scatterplots
  - Graph showing how variable changes with one another

British statistician
Invented methods of correlation and regression
- How closely two variables change with one another
- Ability to preict one variable based on value of another variable

Interested in physics, mathematics, and mind
Wrote Elements of Psychophysics
Psychophysics
- Investigates relationships between physical and psychological worlds
- How can relationships be quantified?
Influenced by Ernst Weber
Both men contribute to Weber’s Law

Difference Threshold
- Smallest difference between two stimuli that’s detected
Trial #1
- Weight #1 → 100g
- Weigh #2 → 101g
- Participant → No difference
Trial #2
- Weight #1 → 100g
- Weight #2 → 104g
- Participant → Difference
Just-noticeable difference (JND)
- The difference between two stimuli participants notice 50% of the time
Trial #3
- Weight #1 → 100g
- Weight #2 → 102g
- Participant → Might be a difference
JND for 100g weight → 2g
JND for 300g weight → 6g
As stimulus increases, JND increases at constant rate
Weber’s Law
- Ratio of magnitude of stimulus to JND is constant
JND for 500g weight