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
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 selection
2.1 Evidence 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.
o If we examine the bodies of living organisms, we can find evidence of dramatic change
Direct Observation of Change Through Time
o Read examples of the change of the Soapberry bug over time on Page 40
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
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
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 45).
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
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
o The resemblance between living and fossil forms in the same region suggests that living
organisms are descended with modification from earlier species.
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
o If this is the case, the fossil record should capture evidence of transformation.
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 picture explanation
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
2.2 Evidence 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
Read example on page 53.
The study of likeness Structural and Developmental Homology
o Organisms show curious similarities in s