Topic 2: Evolution and a history of evolutionary thou
Thursday, September 20, 2018
12:31 PM
Evolution:
- Evolution simple definition: Species change over time.
○ Also phrased as, "descent with modification."
The early views of evolution.
1) Aristotle (keen observer of nature):
a. Ladder-like classification of life. (Scala Naturae/ Scale of Nature.)
i. From non-living organisms at the bottom climbing up ever increasing level
ii. Humans at the very top, but just under God (perfection).
2) Natural theology (Aristotle's classification mixed with biblical account of creation) /fou
a. Organisms created by God
b. Species could never change or become extinct
c. New species could never arise
3) Carolus Linnaeus (1707-1778):
a. Introduced binomial( two-part) species classification (nomenclature) system.
i. E.g, Felis Catus (domestic cat)
b. In this system similar-looking organisms are grouped together.
c. He did not ascribe the animals kinship to anything other than God's design.
d. This discipline is known as taxonomy
Pre-Darwin evolution ideas.
4) Jean Baptiste de Lamarck (1744-1829)
a. First comprehensive theory of evolution:
i. Species change over time.
b. Proposed "perfecting principle":
i. Organisms evolved into more complex one, moving up the Scale of Nature
ii. Microscopic organisms were replaced at the bottom of the ladder by spon
1) Spontaneous generation: simple forms of life arose from non living
c. Famous for the inheritance of acquired characteristics. (Lamarck's giraffe)
i. Proven false today.
Intellectual influences on Darwin
- Jean-Baptiste de Lamarck
- George Cuvier
- James Hutton and Charles Lyell
ught
ls of complexity.
urteenth century:
e.
ntaneous generation.
material
Intellectual influences on Darwin
- Jean-Baptiste de Lamarck
- George Cuvier
- James Hutton and Charles Lyell
The influence of paleontology - Georges Cuvier
○ Fossils in older strata ≠ fossils in newer strata
○ Catastrophism:
§ Speculates each boundary between strata represents a catastrophe
□ Local catastrophes (E.g. floods) wipe out assemblages which are late
□ Past mechanisms ≠ current mechanisms
□ Rejected the idea of evolution
Ideas about geological change- James Hutton (1726- 1797) & Charles Lyell (1797- 187
○ Geologists James Hutton and Charles Lyell
§ Changes in the Earth's surface can result from slow continuous actions stil
○ Lyell's principle of uniformitarianism states:
§ The mechanisms of change are constant over time
□ This view strongly influenced Darwin's thinking
Thomas Malthus
○ Late eighteenth century political economist
○ Published An Essay on the Principle of Population (1798)
§ The human population increases exponentially over time while, at best, ga
modest (arithmetic) increases in food supply.
○ Darwin:
§ Organisms are in competition with one another for limited food and other
§ They have to escape predation and they have to survive often unfavourab
Charles Robert Darwin (1809-1882)
- Dropped out of Medical school to become a naturalist
- At the age of 22, Voyaged on the Beagle around the earth
○ Spent most of his time ashore collecting specimens and making observations
○ He observed that fossils resembled living species from the same region
□ Glyptodont(extinct) / Nine-banded armadillo (still alive)
§ Rather than those of farther regions with similar environments
§ E.g., species on islands often resembles one another but not species from
○ He read Lyell, experienced an earthquake in Chile and observed the uplift of rock
○ He noticed many different species occupied only a small region (South America)
§ These species also resembled others from the nearest continent
§ Darwin hypothesized that plants and animals of the Galapagos were relat
but had changed over time.
er repopulated from other areas.
75)
ll operating today
ains in agricultural technology lead only to
r resources.
ble environments
other islands
ks
)
ted to plants and animals on South America
○ He read Lyell, experienced an earthquake in Chile and observed the uplift of rock
○ He noticed many different species occupied only a small region (South America)
§ These species also resembled others from the nearest continent
§ Darwin hypothesized that plants and animals of the Galapagos were relat
but had changed over time.
- Adaptations
○ In reassessing his observations, Darwin perceived adaptations to the environme
related processes.
○ From studies made years after Darwin's voyage, biologists have concluded that t
speciation are what happened to the Galapagos finches
Darwin's Contributions:
1. Common decent
2. Natural Selection
3. Darwin was an exceptional practitioner of the scientific method
1.
2.
3.
-
Three broad observations that any theory of evolution must explain.
The unity of life (common ancestry)
The diversity of life
The match between organisms and their environment (adaptation)
Darwin explained these observations with the mechanism of natural selection
Based on two observations leading to two inferences
Darwin's publication
- Darwin was slow to publish his findings on these adaptations
- Collected more and more evidence
- Alfred Russel Wallace (1823-1913) reaches similar conclusions, sends manuscript to Da
○ Forces Darwin's hand, Origin of Species published in 1859
§ Succeeded where others failed due to "immaculate and an avalanche of ev
On the Origin of Species by Means of Natural Selection (1859)
- Natural selection:
○ Process in which individuals with favorable inherited traits are more likely to sur
○ In other words:
§ Generation to generation, the mechanism that is causing a population to c
set of traits that gives an individual an advantage over others in the partic
inhabits.
- Evolution:
○ "Evolution" does not appear in 1st ed. Of Origin
§ "Evolved" does
○ "Descent with modification" was the phrase he used
○ Attributes unity of life to descent of all organisms from a common ancestor
○ The Galapagos Islands are home to four distinct species of mockingbird( genius N
ks
)
ted to plants and animals on South America
ent and the origin of new species as closely
these related processes of adaptation and
arwin
vidence"
rvive and reproduce
change, or evolve, is nature selecting for a
cular environment that the population
Nesomimus) which are found on specific
- Evolution:
○ "Evolution" does not appear in 1st ed. Of Origin
§ "Evolved" does
○ "Descent with modification" was the phrase he used
○ Attributes unity of life to descent of all organisms from a common ancestor
○ The Galapagos Islands are home to four distinct species of mockingbird( genius N
islands o the group.
§ It was clear to Darwin that the underlying similarity of the mockingbirds in
shared a common ancestor but that over time, each species had develope
shape, coloration).
§ Simplest explanation:
□ Birds came from mainland South America
□ Colonized most of the islands around the same time.
□ Over thousands of years, the populations that developed on differen
traits diverged.
□ On each island, specific traits would become uniquely modified com
islands.
□ All the species become distinct compared to the ancestral mockingb
mainland.
OBSERVATIONS
Most organisms produce
more than one or two
offspring.
HYPOTHESES
Individuals with a population
compete for limited resources.
A pop
over
heri
Populations do not increase
in size indefinitely.
-
Food and other resources
are limited for most
populations.
Individuals within
populations exhibit
variability in many
characteristics
Hereditary characteristics may allow
some individuals to survive longer
and reproduce more than others.
Many variations appear to
be inherited by subsequent
generations.
□ The evolution of different species of birds on the Islands is tied close
group have different habitats, which resulted in natural selection fav
compared to another.
□ The inherited aspects of an individual that make it better suited to a
Nesomimus) which are found on specific
ndicated that birds from all the islands
ed distinctly different traits (beak size and
nt islands became less and less alike-- their
mpared to the traits od birds inhabiting other
bird species from the South American
PREDICTION
pulations characteristics will change
r the generation’s as advantageous,
itable characteristics become more
common.
ely to the fact that the islands within the
vouring a different set of traits on one island
a particular environment than other
generations.
□ The evolution of different species of birds on the Islands is tied close
group have different habitats, which resulted in natural selection fav
compared to another.
□ The inherited aspects of an individual that make it better suited to a
individuals are referred to as
® Adaptation:
◊ From generation to generation, a species becomes bette
consequence of natural selection.
ely to the fact that the islands within the
vouring a different set of traits on one island
a particular environment than other
er adapted to a specific environment as a