Download Descent with Modification: A Darwinian View of Life

Descent with Modification:
A Darwinian View of Life
Lesson 7.1
Ch. 22
Charles Darwin and TOS
• Published on Nov. 24, 1859
• Two major points:
– Species of organisms on earth today are
descendents of ancestral species that were
different from the modern species.
– Mechanism for this evolutionary process – natural
selection
Natural Selection
• A population can change over generations if
individuals that possess certain heritable traits
leave more offspring than other individuals
• Result of natural selection – evolutionary
adaptation (an accumulation of inherited
characteristics that enhance organisms’ ability to
survive and reproduce in specific environments.
• Evolution – change over time in the genetic
composition of a population
The Evolution Revolution
• Darwin’s (1859) publication flew in the face of both
modern culture AND modern science
– It was not readily accepted by the scientific community
either
• Oldest cultural influence on origins: Genesis
– Each species created perfectly and individually by God
• Aristotle (384-322 B.C.) gave Western culture the
first view of the organization of life outside of
religion
– Scala naturae - ladder of increasing complexity
– each organism had a permanent spot on the ladder
The Evolution Revolution
• Carolus Linnaeus (1707 – 1778) – founder of
taxonomy (naming and organizing species)
– Binomial nomenclature
– Argued that resemblance among species pointed
to the order and pattern in which they were
created
– Darwin later used this to develop his evolutionary
arguments
The Evolution Revolution
• Fossils in sedimentary rock also laid groundwork
for Darwin
• Layers of rock, sand and mud settle over time and
form layers or “strata”
• French paleontologist George Cuvier noticed that
different species appear while others disappear
from strata to strata.
– He was against the idea of gradual evolutionary
change
– Catastrophism – each boundry between strata
represents a catastrophe that destroyed many species
at that time.
The Evolution Revolution
• Gradualism – profound change can take place
through the cumulative effect of slow but
continuous processes
– Valleys were formed by rivers wearing through
rocks and marine fossils were formed from
particles that had eroded from the land and b
The Evolution Revolution
• Uniformitarianism – the same geologic
processes are operating today as in the past,
and at the same rate
– Proposed by the leading geologist of Darwin’s
time, Charles Lyell
The Evolution Revolution
• Lamarck – French biologist who recognized
that evolutionary change explains the fossil
record and organisms’ adaptations to their
environments
– Remembered more for the fact that he described
the incorrect mechanism for this.
– Published theory in 1809 (year Darwin was born)
• Use and disuse (giraffe stretching neck)
• Inheritance of acquired characteristics (giraffe again)
Darwin and TOS
• Father wanted him to go to med school but he
hated it, so he enrolled in Cambridge University
to become a clergyman
– Many interested in science did this: think Mendel
• Rode on the HMS Beagle around the world
with Captain Robert FitzRoy in 1831 (age of 22)
Darwin’s Observations
• Many plants in South America had adapted to
their environments
• Plants in temperate regions of South America
were more similar to plants in tropic regions
of South American than they were to plants of
temperate regions in Europe
• Fossils he found were different, but distinctly
“South American” in comparison to present
species
Galapagos
• Most impacted by stop at the Galapagos
Islands in the south Pacific
– Very unusual species he found there
– Most fascinated by finches – a common bird
elsewhere but somehow different in Galapagos
• Realized that finches’ adaptations were from
having to adapt to the food sources on this
very different island
Publication Process
• Darwin returned to London, staying at home from
illness most of the time, and not publishing his
theories on natural selection and adaptation for
fear of the uproar it would cause
• He was encouraged by Lyell to publish before
someone else.
• June 1858, Alfred Russel Wallace sent a transcript
for Darwin to evaluate, and Darwin quickly sent
his TOS manuscript to publishers
Summary of TOS
• Biological diversity is the product of evolution
• Descent with Modification – unity in life, with
all organisms related through descent from an
ancestor that lived in the remote past. As
descendants from that ancestor moved to
different environments, they had to adapt
– Most branches in evolution are dead ends – 99%
of all species that have ever lived are extinct, so
no gap or link species exist
• Natural selection. Darwin formed his hypothesis of
natural selection by drawing two inferences based on his
observations.
• Observation #1 : Individuals of a population exhibit
variation in their traits.
• Observation #2 : Many traits are heritable.
• Observation #3 : Many species overproduce offspring.
• Observation #4 : Resources are limited; many of these
offspring do not survive due to competition for those
resources.
• Inference #1 (natural selection): Individuals whose traits
give them a high probability of surviving and reproducing
are likely to leave more offspring than others.
• Inference #2 (adaptation): A population will accumulate
favorable traits over generations and become adapted to
its environment.
Summary of TOS
• Artificial Selection – humans have modified
other species over many generations by
selecting and breeding individuals that
possess desired traits
Emphasized Points
• Natural selection may occur between
individuals, but individuals do not evolve,
populations evolve
• Natural selection can amplify or diminish
ONLY heritable traits
Applying Darwin’s Theory
• Natural Selection
– Differential Predation and Guppy Populations
• Due to predation, larger and faster fish were more
dominant in an area, when there was a predator
– Evolution of Drug-Resistant HIV
• Different varieties of HIV exist, and some are resistant
to begin with. After just a few weeks, the resistant
strains comprise 100% of the virus population, due to
selection.
Applying Darwin’ Theory
• Homology, Biogeography, the Fossil Record
– Homology – similarity resulting from common
ancestry
– Anatomical Homology
• Homologous Structures – variations on a structural theme
that is present in common ancestors
– Comparative Embryology – comparison of early stages of animal
development
– Vestigial Organs – structures of marginal, if any, importance to the
organism – once were important to ancestors
– Molecular Homology
• All forms of life use DNA and RNA
Applying Darwin’s Theory
– Biogeography – geographic distributions of species
• Closely related species tend to be found in the same
geographic regions, whereas some ecological niches in
distant regions are occupied by very different (though
sometimes similar-looking) species
• Endemic – species found only in one place in the world
and nowhere else
– Fossil Record
• Prokayotes should be the oldest in the fossil record, and
they seem to be