SC B-5: THE STUDENT WILL DEMONSTRATE UNDERSTANDING

OF BIOLOGICAL EVOLUTION & THE DIVERSITY OF LIFE

DARWIN’S THEORY

Inquiry Activity

Page 368 in bookPage 35 in notebook work in pairsWhen you have calculated your average

length put it on board so class average can be calculated

Also record length of your shortest bean and longest bean: What is the range of the bean length?

CN: PAGE 112 NOTEBOOKTOPIC: Darwin’s theory of EvolutionEQ: What inferences did Darwin make about

Natural Selection from his observations?

DEFINITIONS

1. EVOLUTION: process by which modern organisms have descended from ancient organisms

2. THEORY: well-tested explanation that unifies a broad range of observations

Charles Darwin

Englishman born in 1809

After graduating in 1831 from University took job as a naturalist on H.M.S. Beagle & traveled around the world

Darwin’s Voyage

Darwin

During his travels, Darwin made numerous observations & collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

Darwin’s Observations

1. Plants & animals remarkably well-suited to their surroundings

2. Different organisms lived in same type of ecosystem Example: grasslands of Europe + rabbits but grasslands in Australia - rabbits

Fossils: preserved remains or evidence of an ancient organism

Darwin studied fossils from different continents & noted that some resembled organisms still living & some unlike any creature he had ever seen

Galapagos Islands

Small group of islands off Ecuador

Climates varied from hot & dry to rain forest

Each had different flora & fauna

Galapagos Animals

Darwin’s Hypothesis

Darwin noticed that characteristics of many animals & plants varied noticeably among different islands and hypothesized that they had a common ancestor

Contemporary Ideas that shaped Darwin’s Ideas

1785: James Hutton 1st to present idea that Earth is much older than Bible would indicate Looked at layers of

sedimentary rock with fossils of sea creatures now on mountain top

Looked at geological processes that shape Earth

Reasoned that processes seen today same in past

Origins of Evolutionary Thought

Malthus: 1798Predicted human

population will grow faster than the space & food supplies needed to sustain it

Origins of Evolutionary Thought

Lamark: 1809proposed hypothesis of

inheritance of acquired traits: if parent became

very accurate with bow & arrow after years of practice any child born after would also be very accurate with bow & arrow

Lyell: wrote Principles of Geology (Darwin read 1st vol. while on the Beagle)

Said must explain past events in terms of processes observed now

Lyell’s work influenced Darwin 2 ways:

1. He asked himself: If Earth can change over time why not living organisms?

2. He realized it would take very long time for change to be obvious

Origins of Evolutionary Thoughts

Wallace: 1858Naturalist working in

Malaysiawrote Darwin

speculating on mechanism of evolution by natural selection induced Darwin to publish Origin of the Species in 1859

The Origin of the Species

Darwin returned to England in 1836 and reviewed his observations & notes but did not publish his book for 25 yrs

Darwin proposed a mechanism for evolution that he called: natural selection

Artificial Selection

One of Darwin’s most important insights was that members of each species vary from one another in important ways.

Darwin argued that these small variations were very important using breeders as example

Artificial Selection

Humans choose the natural variations in a species that they found useful and used selective breeding to enhance the traits desired.

Evolution by Natural Selection

Struggle for Existence: members of each species compete for available food, living space, mates Predators that are faster, better nourished,

survive longer, more likely to reproduce more thus passing on those traits that made them faster

Prey that are slightly better at camouflage less likely to be eaten, more likely to reproduce

Survival of the Fittest

Darwin reasoned that a key factor in struggle for existence was how well-suited an individual is to its environment

Fitness: the ability of an individual to survive & reproduce in its specific environment

Adaptations

Adaptation: any inherited characteristic that increase’s an organisms chances of survival

Can be: Anatomical (structure of organism) Physiological (function of organism) Behavioral

Adaptations

Survival of the Fittest

Darwin referred to survival of the fittest as natural selection

Over time the variants in traits that offer an advantage will have increasing incidence in population

Descent with Modification

Term used by Darwin to explain why species today look different from their ancestors: A successful species will just reproduce,

always with some variation in traits until a new stressor appears which will give an advantage to some variations and a disadvantage to others

Variations that give advantage will then become more prevalent in population; others will decrease in #’s

Common Descent

Descent with modification implies all living things have a common ancestor

1. Fossil Record2. Distribution of Species

Dating & comparing fossil shows progression of species over long periods of time

Many species have disappeared

Continental Drift helps explain why similar organisms on different continents

Evidence of Evolution: 4 sources

Continental Drift

3. Homologous Structures

Darwin noticed striking similarities in vertebrates (also seen in plants & algae)

Vestigial Structures: homologous structure that have been reduced in size, no longer serve a purpose (appendix)

Evidence of Evolution

4. Embryology

Many vertebrate embryos go through stage where they look very similar to another species

Evidence of Evolution

Summary of Darwin’s Theory

1. individual organisms differ & some of this variation is inheritable.

2. organisms produce more offspring than can survive & many that do survive don’t reproduce

3. because there are more organisms than can survive they must compete for limited resources

4. individuals best suited to their environment will survive & reproduce passing their successful traits on (causes species to change over time)

5. species today all descended from common ancestors

Strengths Weaknesses

Most of Darwin’s hypotheses have been confirmed

Is considered by many to be the “grand unifying theory of life sciences”

Still does not explain how life began

New information always coming to light: theories change over time

Darwin’s Theory