Transcript Earth History GEOL 2110

Earth History
GEOL 2110
Lectures 5 & 6
EVOLUTION
Major Concepts
• In the late 1700/early 1800’s, a number of natural scientists
had proposed that evolution of life was likely, however,
without a mechanism to explain evolution, the idea was
generally dismissed.
• Darwin’s Origin of Species (1859) not only provided
multiple lines of evidence for evolution, but moreover,
proposed a plausible cause (natural selection).
• With the discovery of genetic theory in the early 1900’s
providing a mechanism for evolution, it became
overwhelmingly accepted as a “fact” of science.
• The genetics within isolated, small populations provided
the triggers for the “origin” of new species
• The mechanisms of evolution are still being figured out, but
not the concept of evolution is not in doubt and has
achieved the status of a paradigm of science.
Early Ideas about Evolution
• To the early Greeks and Romans, the notion
that nature changes/evolves was well
accepted
• Christian teachings required that all organisms
were created together, at once, and
unchanged for all of time
• The notion that God would let organisms go
extinct (as proposed by Cuvier and Smith) was
antithetical to genesis and heritical
Early Ideas about Evolution
Georges de Buffon
Histoire Naturelle (1847)
• defined the concept of species
(the ability to interbreed)
• was the first to emphasize the
importance of environment in the
changes (evolution) within species
• recognized that organism seek to
adapt to their environment but did
not offer an explanation how this
might occur
• noted evidence for inheritance of
traits, but again did not offer an
explanation.
• Enough time for Evolution was a
major sticking point
Early Ideas about Evolution
Erasmus Darwin (1731–1802)
Charles’s Grandfather
• as an animal breeder, recognized
the subtle changes from generation
to generation
• argued that the fitness of an
organism to feed itself, protect itself
against predators, and its ability to
succeed in mating were important
factors controlling its survival and
thereby its ability to pass on these
characteristics to its offspring.
•Still the question remains - how does
inheritance work?
Early Ideas about Evolution
Jean Baptiste de Monet –
Chevalier de LAMARCK
(1744–1829)
Defined “biology” as a study of the
plant and animal world
• Ideas about evolution published in
1809, where he argued that the
fundamental course of nature is change
and this change was controlled by
environment
• Did not ascribe to Buffon’s fixed
species concept, but rather believed
that organism represent a continuum
of change.
•Did not believe in extinction, but
rather the “loss” of an organism was
due to it’s changing into or
replacement by another form.
Inheritance of Acquired Characteristics
Lamarck’s Giraffes
But again, how are these acquired characteristics passed on?
Darwinian Evolution
Charles Darwin
(1809-1882)
•
•
•
Born in the year that Lamarck published
his ideas about evolution
Embarked on a 5-year voyage (18321835) around the world on the HMS
Beagle where he was charged with
documenting the diversity of flora and
fauna in the tropics and Southern
hemisphere.
Struck by:
• Variety of species
• Number and diversity of individuals per
species
• The importance of competition for food,
safety from predators, and shelter
Darwin’s Epiphany
HMS Beagle
Captain Fitzroy
Ship-side Reading
Malthus (1798) Principles of
Population
Lyell (1830) Principles of
Geology
Darwin
Natural Selection
• Natural environments change
• Individuals within a population of
organisms change
• Individual changes that are best fitted
(adapted) to the changes in the
environment are the most likely to
survive
• “survival of the fittest”
Radiation into Environmental Niches
The Finches of the Galapagos
• Only birds on the
islands – no
competition
• 4 different genera
• 15 different
species
• Each adapted a
different beak
type reflecting
their dietary
preference
On the Origin of Species
•
First draft completed in 1839, but
not published until 1859
•
Fearful of backlash from British
scholars and clergy
•
For 20 years, compiled supporting
data
•
Primary goals of the book:
• Document evidence for
Evolution
• Propose a mechanism
(Natural Selection)
Evidence of Evolution
Branching Organization of Life
Early classifications of the
animal and plant kingdom
show groups within
groups within groups
based on anatomical
features
Best portrayed by a
branching family tree
implies related lineages
Today, genetic coding
affirms that grouping
Evidence of Evolution
Homologous Elements
Diverse organisms share similar
organs and features
For example, the bones of
appendages in a variety of
vertabrates
Green –humerus
Red – radius
Blue – ulna
Tan – wrist and phalanges
Evidence of Evolution
Vestigal Structures and Imperfections
Unnecessary body parts
Why would such things
be “created”?
Humans
Tail bones
Appendicies
Evidence of Evolution
Embryonic History
All vertebrate embryos
go through similar early
stages of development
“Ontogeny recapitulates
Phylogeny” Hackel
(1866)
(i.e. embryonic
development repeats
evolutionary history)
Evidence of Evolution
Paleogeography
On unconnected continents,
unrelated animals have evolve to
occupy similar environmental
niches
For example – Marsupials of
Australia
“Ecological Convergence”
Next Lecture
EVOLUTION II
Genetics and the Origin of Species
Quiz #2
Chapter 3
Hypothesis/Theory/Paradigm
The Scientific Method - Seeking understanding
• Observations of phenomenon lead to the
development of multiple possible interpretations or
explanations - hypotheses
• Physical, chemical, mathematical or thought
experiments are devised that attempt to prove the
various hypothesis wrong
• A set of related hypotheses that withstand repeated
testing (are well corroborated) and explain a wide
range of observations develop the status of theory
• Theories that continue to stand up to scrutiny evolve
into paradigm status - largely unquestioned until
too many anomalies develop
Charactersitics of a Scientific Theory
• Based on facts, but not a statement of
certainty or truth
• Testable – holds up to repeated testing
• Predictive – forward and backward in time
• Explains many related natural phenomenon
• Deemed by a majority of scientists to have a
high probability of being correct
Genetic Theory
The Mechanism behind Evolution
• By the mid-1800, the high probability that
evolution happens was generally accepted
• Based on Darwin’s (1859) evidence and well
reasoned arguments, the idea that natural
selection of favorable characteristics within
populations of organisms drove evolution was
also generally accepted.
• However, Darwin did not explain how new
characteristics (and thus new species)
originated
Genetic Theory
The Mechanism behind Evolution
Gregor Mendel (1822-1884)
• Austrian monk, plant breeder
• Devised experiments cross-breeding
pea plants with purple and white
flowers, examining about 28,000 plants
in the course of his experiments.
Pisum
sativum
• He chose peas for his experiments
because he could grow them easily,
develop pure-bred strains, protect
them from cross-pollination, and
control their pollination.
Genetic Theory
The Mechanism behind Evolution
• Mendel discovered that when
cross-breeding purple and white
flower colors, a blended color did
not result, but rather colors
remained distinct with the purple
color being more common
• Morever, the first generation
would produce only purple colors
and in the second generation 25%
of the flowers would be white,
75% purple
• Devised the notion of dominant
and recessive hereditary traits
Genetic Theory
The Mechanism behind Evolution
• Mendel’s results were published in
1865 in an obscure journal, but
was not publicized until ~1900
• Mendel’s laws of heredity formed
the observational foundation of
genetic theory
• In mid-century, the molecular
coding of genes was discovered in
the form of DNA, which occurs in
the nucleus of all cells
Double Helix model for DeoxyriboNucleic Acid
Watson and Crick (1953)
• Variations in genotype (genetic
code) gives rise to variations in
phenotype (physical appearance)
Neo-Darwinism
An Explanation for the Origin of Species
• Natural Selection could explain gradual changes in the
phenotype of an organism (phyletic gradualism), but
what gave rise to abrupt changes and new species?
• The development of population genetics in the 1930’s
& 40’s began looking at evolution by natural selection
in a statistical manner - Synthetic Theory of Evolution
• 1938 – Genetics and the Origin of Species (Dobzhansky)
integrated genetic theory with evolutionary biology
• 1942 – Systematics and the Origin of Species (Mayr) applied
Natural Selection Theory and current species
• 1944 – Tempo and Mode of Evolution (Simpson) showed
evidence evolution in the fossil record
Neo-Darwinism
An Explanation for the Origin of Species
Ernst Mayr (1904-2005)
Systematics and the Origin of Species (1942)
Population Genetics shows:
• The genetics of large populations of
are stable because new character
traits are muted by the large gene
pool; little chance of genetic
differentiation into new species
• In small, isolated populations, genetic anomalies can become
more prominent quickly (founder effect)
• Genetic isolation of a subpopulation that is separated from the
main population, by migration, geographic barriers, or lack of
mobility, causes genetic divergence - allotropic speciation
Neo-Darwinism
An Explanation for the Origin of Species
Punctuated Equilibrium
The theory proposes that most
evolution is marked by long periods
of evolutionary stability, which is
punctuated by rare instances of
branching evolution. This would be
expected from periodic events of
genetic isolation producing allotropic
speciation.
The theory was contrasted against
Stephen J. Gould (1941-2002) phyletic gradualism, the popular
Punctuated equilibria: an
(Darwinian) idea that evolutionary
alternative to phyletic
change is marked by a pattern of
gradualism, with Niles
smooth and continuous change in the
Eldredge (1972).
fossil record.
Phyletic Gradualism?
Or Punctuated Equilibrium?
Evolutionary Changes in the
Fossil Record
• Some species in the fossil record persist for millions of years
relatively unchanged despite significant environmental changes
• Differentiation of species (divergence) is typically subtle
• At certain times when many new ecological niches were
abruptly created (e.g., K-T extinction of the dinosaurs),
divergence resulted in rapid and extreme speciation – adaptive
radiation
• Availability of new niches, can also lead to distinct species
converging on a common body form and dietary preference
(e.g. marsupial evolution in Australia)
• In some cases, certain species can re-acquire traits that were
lost in previous manifestations (iterative evolution), and in
other cases, different species can acquire a similar trait (parallel
evolution)
Parallel Evolution
Oligocene
Hoplophoneus
(relative of dogs
and bears)
Pleistocene
Smilodon
(cat family)
Pliocene
Machairodus
(cat family)
Pliocene (SA)
Thylacosmilus
(opossum
family)
Challenges to NeoDarwinism
Neutralism
• Apparently, organisms have more genetic
variability than they need
• Some of the extra traits may be unaffected by
natural selection, i.e., they are neutral
African Rhino
Indian Rhino
Challenges to NeoDarwinism
Inheritance of Acquired Characteristics (revisited)
• Natural selection implies that rapid responses
to environmental change is not likely
• However, some evolutionary change are
remarkably rapid – immune system
Exposure to disease triggers the immune system
to create (acquire) antibodies
However, some experiments suggest that
immunity can be passed on to offspring.
Challenges to NeoDarwinism
MacroEvolution
• Natural selection is good at explaining
incremental changes (microevolution), but can
it explain dramatic changes, like making an
eye or a wing?
• Possibly not as abrupt as they appear in the
fossil record; many intermediate stages
• Pre-adaptation – organs adapted for one
function change for a new function
Challenges to NeoDarwinism
MacroEvolution
Squid
Evolutionary stages of the mollusk’s eye
Challenges to NeoDarwinism
MacroEvolution – Pre-Adaptation
Transform
-ation of
gill arches
into jaw
bones
The Mexican salamander
(Ambystoma) prefers to stay in its
embryonic state submerged and
breathing with juvenile gills. If
stressed, however, it will emerge
and breath with adult lungs
Evolution and Creation “Science”
A False Equivalence
Evolution is a scientific theory because it is:
• Testable
• Predictable
• Self-correcting
• Open to further refinement
Creationism/Intelligent Design is not a scientific
theory because it is none of the above
Next Lecture
Fundamentals of Stratigraphy
Chapter 4