Download Chapter 5-1 • Darwin`s 4 observations:

Chapter 5-1
• Darwin’s 4 observations:
- diversity (variety)
- differences between bones of fossils and recent species of the
same organism
- differences between the mainland and island organisms
- differences among the same organisms on the islands
• Adaptation: behaviors of organism that make it able to survive or
reproduce in their environment
• Darwin’s observations led to his theory about evolution by natural
selection. Evolution is the gradual change in a species over time.
Nature selects the best suited to the environment; that species will
survive and reproduce.
• Factors that affect natural selection:
- Overproduction: producing more offspring than can survive
- Competition: limited resources
- Variation: differences between individuals of the same species
• Only traits controlled by genes can be acted upon by natural selection.
• Geographic isolation (ex. Continental Drift): new species form
because a group of individuals become separated long enough to
evolve new traits.
Chapter 5-2
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Fossil: preserved remains/traces of an organism that lived in the past (hard parts)
Fossils form when the organism dies and becomes buried in sediments in
sedimentary rocks.
Types of fossils:
- Petrified fossils: minerals in water soak into the buried remains
- Mold/cast: hard parts get dissolved; the empty space, the mold, gets filled
with minerals. Now it is called a cast.
- Whole organism: preserved in ice, tar, or sap
Determining the fossil’s age:
- Relative Dating: fossils in bottom layers are older. This is true if the
layers remain undisturbed.
- Absolute Dating: tells the actual age using the half-life (time for half of
the atoms of the element to change into another element) of radioactive
elements that break down easily into other elements
The fossil record includes the millions of fossils collected. What do fossils
reveal:
- if species have become extinct
- how fast the organisms moved (footprints)
- how tall the organisms were (skeleton)
- what the organisms ate (teeth)
- Earth conditions and age
- evolution
- if organisms lived in groups or alone
Geologic Time Scale: “calendar” of Earth’s events of 4.6 billion years; divided
into the largest time spans called eras, then periods, and then epochs each
characterized by different Earth conditions and organisms:
- The largest time span is the Precambrian Time; very little is known about
it because the organisms that lived at that time were probably soft and
didn’t leave many fossils.
- The Paleozoic Era: ancient
- The Mesozoic Era: middle
- The Cenozoic Era: recent
How fast evolution occurs? 2 theories:
- Gradualism: evolution is slow but steady; tiny changes that add up and
therefore intermediate forms occur; Darwin thought this way.
- Punctuated Equilibria: evolution happens during short periods of rapid
change followed by long periods of little/no change; no intermediate forms
occur
Chapter 5-3
1. Other evidences of evolution:
• similarities in body structure (# and arrangement of the bones):
homologous structures
• similarities in early development: similar embryonic development
• similarities in DNA: similar base pairs
These suggest they have a common ancestor.
2. Branching Tree: a diagram that shows how groups of organisms are
related. See page 169.