BGYB51: Chapter 2 (Pages 37 – 49 and 53 – 65)
The Pattern of Evolution
• The first scientist to give a definition of species, John Ray, states that “…[O]ne
species never springs from the seed of another.”
• The Theory of Special Creation had been the leading explanation in Europe for
the origin of species until a certain point where scholars began to challenge
that notion (i.e. when Darwin started to study biology seriously) and research
in biology and geology grew rapidly to disprove the theory.
• Darwin drew up evidence suggesting that the pattern of life’s history is
different than is claimed by Special Creation. (Read Page 39 for elaboration)
1. Species are not immutable, but change through time
2. Species are derived not independently, but from common ancestors
3. The Earth and life are considerably more than 6 000 years old.
• Darwin also introduced a process to explain this pattern called natural
2.1Evidence of Change through Time
Evidence from Living Species
• The living evidence for descent with modification comes in two forms:
o By monitoring natural populations, we can directly observe small scale
change (i.e. microevolution)
o If we examine the bodies of living organisms, we can find evidence of
dramatic change (i.e. macroevolution)
• Direct Observation of Change Through Time
o Read examples of the change of the Soapberry bug over time on Page
• Vestigial Organs
o A vestigial structure is a useless or rudimentary vision of a body part
that has an important function in other, closely allied species (e.g. the
remnant hind limbs on the rubber boa).
o Humans have muscles attached to the hair follicles that make hair stand
up when cold, intimidated, or needed to seem bigger. These muscles are
effective for animals that are very hairy like chimpanzees. Most of us are
not that hairy (except some of you hormone excessive freaks), and thus
the result of these muscles contracting is goose bumps. This implies that
we descended from ancestors who were hairier than us.
o Read page 42 for more examples
o Vestigial traits also occur at a molecular level.
Humans have one on chromosome 6; a DNA sequence that looks
like a gene for the enzyme CMAH
It is actually disabled by a 92-base-pair deletion and humans
cannot manufacture CMAH
Chimpanzees however are able to
This explains that the human race must have descended from a
common ancestor with the chimpanzees
o Read page 43 for more examples Evidence from the Fossil Record
• Fossil: a trace of any organism that lived in the past
• Fossil record: the total, worldwide collection of fossils
• The Fact of Extinction
o The fact that many species have gone extinct suggests that Earth’s flora
and fauna have changed over time (an example of this on page 44 and
• The Law of Succession
o Fossils and living organisms in the same geographic region are related
to each other and are distinctly different from organisms found in other
areas (e.g. Australia and Argentina).
o The mammalian faunas of two continents are obviously different, yet
each continent’s extant fauna is strikingly similar to the continent’s
recent fossil forms the law of succession
o The resemblance between living and fossil forms in the same region
suggests that living organisms are descended with modification from
• Transitional Forms
o Darwin asserted that species are descended with modification from
earlier form and that fossils represent pas populations, some of which
were ancestors of species alive today.
o If this is the case, the fossil record should capture evidence of
Transitional species should show a mix of features of the
ancestral population as well as novel traits of later descendants.
Guess what? THEY DO!
o A great example is the Archaeopteryx. It was a birdlike creature with a
dinosaurian appearance. This species demonstrates the past existence
of species intermediate in form between dinosaur and bird.
It also indicates that birds became birds by first developing
features before the skeletal and muscular modifications
associated with flight of modern day birds
o Read page 48 & 49 for more examples and see Figure 2.13 for a sick
Evidence of Descent with Modification
• The evidence shows that species change over time on a microevolutionary
scale (e.g. soapberry bugs evolving shorter beaks)
• Evidence also shows that species change over time on a macroevolutionary
scale (e.g. birds from dinosaurs)
2.2Evidence of Common Ancestry
• Some species appear to be in the process of splitting into two. Freely
interbreeding populations connect the entire species, but members of certain
populations do not interbreed (e.g. greenish warbler).
• Read example on page 53. Homology
• The study of likeness
• Structural and Developmental Homology
o Organisms show curious similarities in structure and development
unrelated to function. Thes