8.1: Scientific Contributions to a Theory of Evolution
pg. 326 - 331
Key Terms: paleontology, catastrophism, uniformitarianism,
inheritance of acquired characteristics, theory of evolution by
natural selection, evolution, survival of the fittest, and descent with
modifications.
“Where did we come from?” has been debated for thousands of
years. The first explanations of life were influenced by religion and
philosophy, and all life forms have existed, unchanged since their
creation.
1600’s introduced empirical studies to explain the natural world,
through observation and experimentation to form new ideas and
hypotheses about nature.
John Ray (1627 – 1705) first used empirical studies to classify
plants and animals based on anatomy and physiology. Carolus
Linnaeus (1707 – 1778) extended the classification system.
Georges-Louis Leclerc, Comte de Buffon (1707 – 1788)
Was one of the first to challenge the idea that life forms are
unchanging, explained in his 44 - volume Historie Naturelle.
Buffon noted similarities and difference between humans and apes,
and speculated that they may have a common ancestor, suggesting
the species has changed over time. Buffoon also suggested that
Earth was more then 6000 years old, as originally believed. His
ideas led others to question whether life is unchanging.
The Science of Paleontology
Fossils are important part to the study of evolution. Fossils are
preserved remains of once-living organisms.
Georges Cuvier (1769 – 1832) studied fossils, and is accredited
with developing the science of paleontology, the study of ancient
life through the examination of fossils.
Paleontology – is the study of ancient life through the examination
of fossils.
Cuvier determined that in each stratum (layer of rock) is
characterized by a unique group of fossil species, also the deeper
(older) stratum, the more dissimilar the species are from the
modern versions. Cuvier determined that new species appeared and
others disappeared over time and species can become extinct.
Figure 8.2: Deep rock strata are older than strata closer to the surface. Different species
of fossilized organisms can be found in different sedimentary rock strata. This is evidence
that not all life forms came into existence at the same time.
Catastrophism
Cuvier explained his observations by proposing the idea that the
Earth experienced many destructive natural events in the past, such
as; floods, and volcanic eruptions. These events were violent
enough to have killed numerous species each time they occurred,
which he called revolutions.
After these revolutions or catastrophes, the area would be
repopulated by organisms from other nearby unaffected areas,
explaining why fossils of species that did not exist any more was
found in the stratum.
Catastrophism – is the idea that catastrophes such as floods,
diseases, and droughts periodically destroyed species living in a
particular region, allowing species from neighbouring regions to
repopulate the area?
Charles Lyell (1797 – 1875)
Lyell did not accept Cuvier’s theory of catastrophism, but
proposed his own theory of uniformitarianism. His theory was
based on geologist’s James Hutton’s idea that geological processes
are operating at the same rate as in the past. If geological processes
are slow and continuous rather than catastrophic (building and
eroding mountains), the Earth might be more than 6000 years old.
Even though these changes occur over long periods of time, it still
resulted in substantial changes. If Earth is slowly changing, could
populations change also occur slowly?
Uniformitarianism – is Charles Lyell’s theory (based on Hutton’s
theory) that geological processes operated at the same rates in the
past as they do today.
Learning Check: questions 1 – 6, pg. 327
Jean-Baptiste Lamarck (1744 – 1829)
Lamarck outlined his ideas about changes in species over time, by
comparing current species of animals with fossil forms. He
observed a “line of decent” or progression in which a series of
fossils (from older to more recent) led to modern species.
Lamarck believed the organisms would become better adapted to
their environments. Any body parts used more often to survive
would become larger and stronger, such as; the giraffe that
developed longer necks and tongues to eat leaves higher up in the
trees. He theorized that these developments would be passed on to
their offspring, calling it Inheritance of acquired characteristics.
Also the body parts not used would disappear or not be passed on.
The importance to Lamarck’s theory is the fact that the
environment, and the organism’s adaptation to the environment,
resulted in characteristics that could be passed on to the next
generation.
Inheritance of acquired characteristics – is the idea that
characteristics acquired during an organism’s lifetime can be
passed on to its offspring.
Charles Darwin (1809 – 1882)
In 1831, Darwin at age 22; sailed on the HMS Beagle with the
primary purpose of surveying and mapping the coast of South
America. During the voyage Darwin also had the opportunity to
explore these new lands.
His observations and ideas later became his theory of evolution.
His main five observations and questions were:
Observation:
1. The flora and fauna of the different regions visited were distinct from
those found in England and Europe.
2. Fossils of extinct animals looked very similar to living animals
3. Animals (finches) observed on the Galapagos Islands closely
resembled animals he had observed on the west coast of South
America.
4. Animals (finches) on the Galapagos Islands varied slightly from
island to island.
5. Traits can be passed on from parent to offspring, and through sexual
reproduction, variations within the species is occurs.
Questions:
1. If all organisms originated in their present form in one singular event,
why were there distinctive clusters of similar organisms in different
regions of the world? Why were all types of organisms not randomly
distributed?
2. Why would live and fossilized organisms that looked similar be found
in the same region?
3. Why did the Galapagos species so closely resemble organisms on the
adjacent South American coastline?
4. Why was there such diversity of species in such a small area? Could
these species have been modified from an ancestral form that arrived
on the Galapagos Islands shortly after the islands were formed?
5. Could a process similar to artificial selection also operate in nature?
Theory of evolution by natural selection – is a theory explaining
how life has changed, and continues to change, during Earth’s
history.
Evolution – is the process of genetic change in a population over
time.
Darwin, Wallace, and the Theory of Evolution by Natural
Selection
Alfred Russel Wallace (1823 – 1913) was developing similar
conclusions to Darwin’s. Populations change over time, but the
question is what was the mechanism for these changes.
Thomas Malthus (1766 – 1834) wrote an essay called an Essay on
the Principles of Population, which introduced the key idea used
by Darwin. Malthus suggested that populations produce far more
offspring than their environment (food, shelter, and mates) can
support. Starving and disease were factors to reductions in
population.
Darwin accepted Malthus’ premise and suggested that organisms
with traits that helped them survive their environments were more
likely pass on to their offspring.
Darwin reasoned that through competition for limited resources
between individuals of the same species would select for
individuals with favourable traits, traits that increased their
chances to survive and reproduce.
As the population grows from generation to generation the
proportion of the trait occurring in the population increases. This is
the idea of Survival of the Fittest and Darwin called it natural
selection. Darwin published his findings in 1859, The Origins of
Species.
Darwin’s theory of natural selection showed how populations of
individual species became better adapted to their environments
over time.
Summary:
1. Organisms produce more offspring than can survive.
Therefore, organisms compete for limited resources.
2. Individuals of a population vary extensively, and much of
this variation is heritable.
3. Individuals that are better suited to local conditions survive
to produce more offspring.
4. Processes for change are slow and gradual.
Survival of the Fittest – is the idea that the organisms that are the
fittest leave the most offspring, so those organisms win the
struggle for survival; phrase coined by John Spencer.
Descent with Modification
Darwin discussed the decent of modification instead of evolution
in his book The Origins of Species. He believed the evolution
meant progression or getting better, but natural selection does not
demonstrate progress, and has no set direction. It is on based on
individuals in the population that have the ability to survive the
local environmental conditions and these traits are passed on.
Decent with Modification - is Darwin’s theory that natural
selection does not demonstrate progress, but merely results from a
species’ ability to survive local conditions at a specific time.
Review Questions:
1 – 15
pg. 331
Activity 8.1: Building a Theory
pg. 330
Thought Lab 8 – A: Comparing the Ideas of
Lamarck and Darwin
pg. 341
Study Guide:
Self Assessment 1 – 14
SG. 118 – 119
Developing the Theory of Evolution by Natural Selection (8.1)
1 – 4, SG. 120 – 122