Unit 3: Evolution and Natural Selection
Where Did We Come From?: Evidence of Evolution
Charles Darwin and the Theory of Evolution
Alfred Russel Wallace- British naturalist, also came up with idea of evolution by natural selection
-independently came to similar conclusions around time Darwin published his book
-published preliminary ideas a year before Darwin
Jean-Baptiste Lamarck- first put forth the idea of evolution, hypothesized inheritance of traits
-first to state clearly that organisms adapt to their environments
Thomas Malthus- wrote essay on principle of population where he observed populations growing
exponentially but eventually limited by resources --reach carrying capacity--inspired Darwins theory of
natural selection which he called the “struggle for existence”
Charles Darwin:
-British naturalist who proposed an alternative view of how species arose
-concluded “living things are related” and have changed over millions of years
-dropped out of medical school
-went against what everyone during his time believed
-entered university to study for ministry (urged by father)
-Charles Darwin proposed how different species of animals arose
Species- group of individuals that regularly breed together - distinct from other species in appearance or
behavior
The Origin of Species:
1/ Theory of common descent- species change over time and have a common ancestor
(they evolve)
2/ Theory of Natural selection- explains how organisms evolved from common ancestor
to become great variety seen today
- process by which individuals with certain traits survive and reproduce more
than individuals who lack these traits
-physical or behavioral traits f organisms that lead to increased survival or
reproduction in particular environment (less desirable traits are lost)
Voyage of the Beagle
-professor John Henslow nurtured Darwin’s curiosity for natural world
-Henslow secured Darwin’s first job after graduation
-1831 when he was 22 began 5 year voyage -- HMS Beagle-life-defining journey
-Beagles mission was to chart coasts and harbors of South America (naturalists job was to collect,
observe and note anything worthy in natural history)Henslow recommended Darwin to be unpaid
assistant naturalist
-Darwin was strongly influenced by stop in Galapagos, small volcanic island off the coast of Ecuador
-many birds and reptiles Darwin observed seemed to be unique to each island
-while all islands had tortoises, the type found on each island differed
-Darwin wondered why God would place different types to tortoises on islands
History of the Theory of Evolution
-Greek myths proposed a god or many gods created life on earth (creationism)
-Judeo-Christian believed God created all life on earth in its current form within a short period of time
(based on Biblical texts) –worldview dominated Western thought during 17 and 18 centuries
Special creation-hypothesis that all living organisms on Earth arouse as result of actions of supernatural
creator
Evolution- changes in the features (traits) of individuals in a biological population that occur over the
course of generations (changes in frequency of alleles within a gene pool from one generation to the next)
Theory of evolution- all organisms on Earth today are descendants of a single ancestor that arose during
the distant past
Convergent evolution- evolution of the same trait in different populations due to shared environmental
conditions and not shared ancestry Unit 3: Evolution and Natural Selection
Evolution and Common Descent
Hypothesis about origin of modern organisms:
1. Static model hypothesis- assertion
that organisms have not changed
substantially since their creation
-rejected hypothesis as earth is
far older than 10 000 years and
species have clearly changed over
time
2.Transformation hypothesis-All living
organisms were created, perhaps even
millions of years ago, and that changes
have occurred by microevolution in
these species, but that brand new
species have not arisen
-rejected hypothesis-evidence of
relationships among organisms about
3. Separate types hypothesis-different
types of organisms (plants, animals, insects) arose
separately and since their origin have diversified
into numerous species
-rejected hypothesis- universality of DNA genetic
code and cell components are evidence of a single
origin of all life
4. Common descent-theory that all
living organisms on Earth descended
from a single common ancestor that
appeared in the distant past
- supported hypothesis –wide variety of evidence including comparative anatomy, DNA
sequences, and the fossil record
Linnean Classification
-Carl von Linne, (Carolus Linnaeus) Swedish physician and botanist, gave all species and organism a two
part, or binomial name in Latin (common language at time)
-the names he assigned to organisms typically contained information about the species traits (Acer
rubrum is Latin for “maple tree that produces sugar” and acer saccarhum is Latin for red maple)
-all species with name Acer are all maples
-created logical system to organize diversity-grouping organisms in hierarchy
Theory of Evolution
*Theory of evolution sometimes called “Darwinism”
-idea that life started as a single organism and that, as its descendants moved to new habitats (or habitats
changed) they underwent modifications/adaptations to help them survive, thus creating diversity of
species for on earth
-evolution is gradual change of living organisms over time
-today, almost all scientists view evolution as a truth (as sure as gravity) because of the vast amount of
evidence Unit 3: Evolution and Natural Selection Unit 3: Evolution and Natural Selection
DNA- molecule of heredity that carries the information about the body plan of an organism.
Gene- specific part of
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