Transcript History, Science and Life

Welcome to
Introductory Biology II
Organismic and Evolutionary Biology
(BIOL 202)
Comparative Genomics helps
elucidate ancestor/descendent
relationships among major
lineages of mammals, from the
primordial mammal, with an early
divergence of montremes, then
marsupials, then placentals,
including primates and their close
relatives the bats.
Lecture Topics in Unit I:
Evolutionary Processes
•History, Science and Life
•How populations evolve
•What species are and how they arise
•Macroevolution; patterns and process
•How to determine evolutionary relationships
•How molecules and genomes evolve
Today’s Topics:
•Descent with modification;
development of evolutionary thinking
•History of Life on Earth
•Classification
•Scientific Inquiry
Fossils of the large (15-30 cm)
soft-bodied organisms
Pteridinum simplex are locally
abundant in sandstone beds of
the terminal Proterozoic (~550
my old) Nama group in Namibia.
New insights from paleontology,
geochemistry and molecular
genetics are collectively
illuminating the pattern,
developmental basis, and
environmental context of early
animal evolution
Lecture 1:
History, Life and Science
What Darwin and Wallace Figured Out
•Evolution happens; species’ characters (traits) change over time and indeed
such evolutionary change may result in origin of new species from existing ones
•Natural selection drives evolution; evolution is a consequence
•Diversity of life on earth is the consequence of evolution, and all organisms,
ultimately, share a common ancestry
A young Charles Darwin, and a reproduction of the HMS Beagle
Prevailing Ideas about Life, Change and Evolution arose in Ancient Greece
•Scientific inquiry arose with the Ancient Materialists of Greece and Her Colonies
(5th, 6th century BC)
•Methodically applied observation and logic to problem solving
•(eg, Anaximander, Empedocles)
•Classical Traditionalists of Greece and her Colonies (4th and 3rd
century BC) departed from the “scientific approach” of their
predecessors.
•Culminated in writings of Plato and Arisotle
• Plato’s Theory of Forms (Eidos)
• Aristotle
• Father of Modern Biology
• Applied Plato’s theory of forms to living things
• Developed important, unifying, enduring biological concept; Scala
naturae
•Aristotle’s non-evolutionary concepts, including immutability of species and
“Scala Naturae” that were incorporated in Christian Theology and remained
the principal model of biological thought for 2000 years – until the 18th
century
Emergence of Scientific Thinking
Arose with the Breakdown of
Classical Tradition -- in the1500’s
Contributing factors to that breakdown
•Renaissance
•Global Exploration
•Protestant Reformation
Important contributors to “new”
approaches to Knowledge
•Gutenberg
•Copernicus
•Thomas Aquinas
•Francis Bacon
•Redi
World exploration, the renaissance, the protestant
reformation…all contributed to a new intellectual
atmosphere that led to the advance of scientific empiricism
and rationalistic thinking
Intellectual Climate of Darwin’s Era (late
1700’s-Origin)
•William Paley and others develop and promote
Natural Theology, which pervades European and
American Science
•Carolus Linnaeus establishes huge intellectual
model; Systema naturae
•Inception of modern systematics, built on
Aristotelian Scala naturae; non-evolutionary
•New Sciences of Geology and Paleontology are
strong intellectual influences
•Catastrophism and progressionism prevailed
in many early cultures and were incorporated
in Geology – toppled by theories of
gradualism and uniformitarianism of Hutton
and Lyell
•Growing knowledge of geological processes
leads to questions regarding age of earth
19th Century England: The Intellectual Context in which Darwin
Developed His Ideas
Important concepts, publications that strongly influenced early 19th century
scientific thinking
-Botanist Carolus Linneaus
-Reverend William Paley
-Ettiene George St. Hillaire
-Cuvier
Systema Naturae
Natural Theology
Environmentalism
Catastrophism
Radical 19th century geological concepts about the nature and pace of
geological processes –age of earth- that influenced Darwin’s thinking during
the voyage
-Geologist Hutton
-Geologist Lyell
Gradualism
Uniformitarianism
Concept that influenced Darwin’s thinking after the voyage
-Thomas Malthus
An Essay on Population
The Voyage of the Beagle
Course of the HMS Beagle’s World Journey
Continental comparisons of floras and faunas
Taxa showed continental affinities --even to the point that plants and animals
from temperate South America showed a stronger affinity to those of tropical
South America than those of temperate Europe
Within-continent comparisons of fossil and living taxa
Found fossils of extinct taxa that appeared to be ancestral to living
taxa found there – i.e., distinct resemblances to living South American
taxa
Unique “species groups” with curious
distributions on the Galapagos Islands
Found that most species were “endemic”, yet
bore resemblance to South American taxa
with unique distribution on the archipelago
From the Beagle to “Origin”
Darwin turned his “post-Beagle” attention to:
•Artificial Selection
•Population Theory of Thomas Malthus
Published “Origins” some 20 years after his
voyage
•Central Thesis of Origins: Descent
with modification results in a branching
tree of species, in which related species
share common ancestry
The mathematical model on which
Thomas Malthus based his
hypothesis; food production is
arithmetic, population growth is
geometric (An Essay on the Principal
of Population, 1778)
Darwin studied domestic pigeons, which were subjected to
artificial selection by pigeon fanciers to such an extent that the
various races produced showed levels of differentiation that one
might expect among species
Darwin’s Line of Reasoning in Support of Descent with Modification
(Evolution through Natural Selection)
Observation 1. All species have potential fertility for exponential population growth
Observation 2. Populations tend to remain stable in size
Observation 3. Environmental resources are limited
Inference 1: More individuals are produced than can survive; struggle for existence
leads to survival of a fraction of offspring each generation; differential survival
Observation 4: Individuals within a population vary extensively in their characteristics
Observation 5. Much variation is heritable
Inference 2. Survival is not random; depends in part on hereditary makeup;
individuals with inherited traits best fit to the environment are likely to have more
offspring than others; differential reproduction
Inference 3. Unequal survival and reproduction will lead to gradual change in a
population, with favorable characteristics accumulating over generations
Darwin developed his idea of Evolution, of descent with
modification, on five ideas that are each now regarded as theories
(well-supported ideas with broad explanatory power)
1.Perpetual Change. Life is very old and life forms undergo perpetual intergenerational change in form and diversity
2.Common Descent. All life forms share a common ancestry.
3.Multiplication of Species. New species arise from pre-existing species
4.Gradualism. Large differences in form among species is due to incremental
accumulation of many small differences over long periods of time
5.Natural Selection. Organisms in a population experience differential survival
and reproduction as a consequence of variability in heritable traits.
History of Life on Earth
•Earth is more than 5 billion
years old
•Life originated some 3.5
billion years ago
•Diversification of life has
ensued only in the last 10% of
Earth’s existence
•That 600 million years
includes the Paleozoic,
Mesozoic and Cenozoic Eras
Continental Drift. Earth’s crust consists of moving
plates some 40 km thick, suspend on a molten,
fluid mantle
Much of our knowledge on the
history of life on Earth is based
on interpretation of fossils -- the
Fossil Record
History of
Earth and
Life
1000
Oldest Eukaryotic fossils
2000
3000
Accum. of atmospheric. O2
and evolution of aerobic
respiration
Photosynthesis evolves
Oldest prokaryotic fossils
Origin of life - anaerobic
4000
Earth Cools
5000
Earth forms 5+ billion
years ago
~ 2 billion years
of a strictly
prokaryotic
world!!
RNA sequence
data shows
Bacteria and
Archaea diverged
early, about 3
billion years ago
Beginning of Paleozoic Era
1000
History of
Earth and
Life
Oldest Eukaryotic fossils
Symbiotic theory of
origin of Eukaryotes
2000
Substantial atmospheric O2
Photosynthesis evolves
3000
Oldest prokaryotic fossils
Origin of life
4000
5000
Earth Cools
Earth forms
Eras are bounded by major faunal turnovers that are thought
to be related to cataclysmic phenomena of global dimensions
Cenozoic Era
~65
mya
Mesozoic Era
Laurasia
Gondwana
Pangea
Paleozoic Era
~250
mya
A thin band rich in iridium marks the boundary between rocks
deposited in the Cretaceous and the Tertiary Periods
Cenozoic Era
Mesozoic Era
Paleozoic Era
H
C
Periods of cold
climates and
glaciations have
punctuated
Earth’s history
Today
Paleozoic
~600 mya
Mesozoic
~250 mya
~65 mya
Phanerozoic Eon
(Time of “visible” life)
Paleozoic Era
(Time of “Old Animals”)
Mesozoic Era
(Time of “Middle Animals”)
Cenozoic Era
(Time of “New Animals”)
Cenozoic
Paleozoic Era
Precambrian
Cambrian
~600 mya
~500 mya
~250 mya
•The Cambrian Period is the oldest geological period from
which fossils of relatively complex organisms are represented
•Most of the extant (currently living) phyla are represented in
the Cambrian, but not before.
Evolutionary tree of
vertebrate animals and
close relatives
Width of the track
indicates relative
species abundance of
each group through
geological time
PreCambrian
Paleozoic
Mesozoic Cenozoic
Mass Extinctions and the Geological Time Scale
A Mass Extinction is the widespread extinction of many taxa,
globally, that occurs in a relatively brief period of geologic time.
Many of the periods between periods, and between eras, are
demarcated by mass extinctions
Two important mass extinctions to be aware of, now, are the:
•Permian Extinctions (“ended” the Paleozoic Era)
•K/T Extinctions (“ended the Mesozoic Era)
Changes in numbers of families of marine invertebrate and vertebrate
animals; five major extinctions since the Cambrian Explosion
Along the coast of Tethys, an
ancient warm ocean that
stretched from Spain to
Indonesia, an undulating
Basilosaurus catches fish with
its four-foot long jaws and
battery of sharp teeth
(Valkenburgh. Natural History.
April 1994)
Evolutionary patterns in the
rocks; Ambulocetus natans is
an important find and a useful
case study
Fossil formation in sedimentary deposits
Edinburgh Scotland
Dating Fossils
•Relative Dating
Absolute Dating of Fossils and Rocks:
Radiometric Dating
Radiometric Dating; Using decay rates of radioisotopes to
accurately estimate age of a fossils and rocks
Radioactive isotopes can be detected and their amounts measured by the radiation they emit as
they decompose to more stable atoms.
•Paleontologists use the clocklike decay of radioactive isotopes to date fossils and rocks
Emergence of Scientific Thinking Arose with the Breakdown of
Classical Tradition -- in the1500’s
•Renaissance
•Global Exploration
•Protestant Reformation
Intellectual Climate of Darwins Era (late 1700’s-Origin)
Natural Theology, ala William Paley, pervades European and
American Science
Carolus Linnaeus establishes huge intellectual model; ________
_____________
Intellectual Climate of Darwins Era (late 1700’s-Origin)
William Paley and others develop and promote Natural Theology,
which pervades European and American Science
Carolus Linnaeus establishes huge intellectual model; Systema
naturae
•Inception of modern systematics, built on Aristotelian Scala
naturae; non-evolutionary
New Sciences of Geology and Paleontology are strong
intellectual influences…
•Catastrophism of Georges Cuvier
•Gradualism of Hutton
•Uniformitarianism of Lyell
•Environmental Determinism
Charles Darwin (1809-1882) and Darwinism
Charles Darwin
…Rich kid; natural-born naturalist and observationist;
graduated Cambridge having studied religion and medicine
...Credited with figuring out that “natural selection” imposes
character changes (adaptations) on populatons over time, one
outcome being “speciation”, such that “diversity” is the
consequence of a “species branching process”
...collected and synthesized a compelling body of information
to back it up -- voyage of the Beagle (1831-1836)
•published it -- Origin of Species 1859
Voyage of the Beagle
•Cape Verde Island
•Brazil to Tierra del Fuego
•The Galapagos Islands
From the Beagle to Origin
•Artificial Selection
•Population Theory of Thomas Malthus
•Central Thesis of Origins: Descent with modification results
in a branching tree of species, in which related species share
common ancestry
Ernst Mayr’s formalization of Darwin’s Theory
(stated as inferences based on observations)
Scientific Inquiry
Scientific enterprise
•Describe natural systems (recognize patterns, phenomena)
•Develop causal explanations (figure out underlying processes)
Scientific Inquiry
Scientific enterprise
•Describe natural systems (recognize patterns, phenomena)
•Develop causal explanations (figure out underlying processes)
Hypothesis-testing (hypothetico-deductive reasoning)
•Identifiy problem/question
•Conceive an explanation (hypothesis)
•Conceive (deduce) a falsifiable prediction
•Test prediction
(if false)
Causal Explanations Lie at Two Levels
•Proximate Explanations
•the mechanistic “how” explanations
•answers tend to be rooted in cell-, tissue- and organlevel physiological processes
•often amenable to experimental approaches of
hypothesis testing
•Ultimate Explanations
•the evolutionary “why” explanations
•often amenable to experimental approaches, but also
often best approached with comparative methods
Strength of Inference
•Generally speaking, experimental approach is considered a
stronger form of inference. Why?
Strength of Inference
•Generally speaking, experimental approach is considered a
stronger form of inference. Why?
•One can control all but a single variable in an
experiment, ruling out alternative competing explanations
•Causation is more firmly established (than in
comparative work), because manipulation, tweaking, of
one variable has a specific effect that is predicatable in
space and time
Strength of Inference
•Generally speaking, comparative approach is considered a
weaker form of inference. Why?
•One can’t control all but a single variable
•The results are often lead to correlations that fall short of
making a compelling case for causation (one variable
actually “causing” the change in another variable)
Scientific Inquiry
Scientific enterprise
•Describe natural systems (recognize patterns, phenomena)
•Develop causal explanations (figure out underlying processes)
Hypothesis-testing (hypothetico-deductive reasoning)
•Identifiy problem/question
•Conceive an explanation (hypothesis)
•Conceive (deduce) a falsifiable prediction
New Sciences of Geology and Paleontology are strong intellectual
influences…
•Catastrophism of Georges Cuvier
•Gradualism of Hutton
•Uniformitarianism of Lyell
•Environmental Determinism
Pre-Origins Ideas about Evolution
•Inheritance of Acquired Characteristics of Lamarck
Continental Drift:
Earths land masses
existed as a “super
continent” 250 million
years ago
How does “evolution” happen at the population level?
…mutation, migration, non-random mating, genetic drift…
and natural selection
What is “natural selection”?
…differential reproduction and mortality
What is “fitness”?
…relative reproductive contribution to subsequent generations
•a. the exponential decline in radioactivity of
carbon 14. This siotope has a half-life of 5600
yrs; half the c14 in a specimen will be gone in
5600, half of the remainder will be gone in
another 5600 years, half the remainder will be
gone in another 5600, etc
•Use of C14 dating to determin age of a fossilized
clam shell. Because the half life of C14 is
relativel short, this isotope is only reliable for
dating fossils less than about 50,000 yrs old. To
date older fossils, paleontologists use radioactive
isotopes with longer half lives. Radiometric
dating has an error factor of less than 10%.