Transcript Lecture 3

BIOLOGY 3404F
EVOLUTION OF PLANTS
Fall 2008
Lecture 3
Tuesday September 23
Evolution
• We will cover the basics of evolution much more briefly
than I would normally in first year G Bio. I assume that
you had such an introduction to evolution in Bio 22 or 23,
and that much of what we cover today (and in Chapter 11)
is review.
• Charles Darwin and Alfred Russell Wallace are usually
credited with developing the theory of evolution (both
published in 1859). However, the idea of evolution was
not entirely new with either
Evolution: history of an idea
• Anaximander (610-546? BC) believed that life arose in
water, and that more complex forms arose from simpler
ones.
• Aristotle (384-322 BC) believed that species were fixed,
and do not evolve.
• Other Greeks held that species (including man) were
originally created in their “ultimate form” and that they are
all gradually degenerating over time (“devolution”).
Evolution: history of an idea, II
• Christian doctrine held that the Earth was
created, and not ancient; Irish Archbishop
James Ussher (1581-1656) put a date on the
Creation at 4004 BC. How old is it?
• The discovery of fossils (preserved remains
of prehistoric organisms) suggested a much
earlier origin for Earth.
• French naturalist Buffon (1707-1788) raised
the possibility that existing organisms had
arisen from fossilized ones, but then argued
against the idea.
Evolution: history of an idea, III
• Another French naturalist, Lamarck (17441829), seriously proposed evolution, but as
a mechanism proposed the inheritance of
acquired characteristics.
• His ideas were not widely accepted, and his
proposed mechanism is rejected today, but
his writings served to shake existing views
on special creation.
Evolution: history of an idea, IV
• Read about Charles Darwin’s (1809-1882) Voyage
of the Beagle (1831-1836) in the text, or in his
own words in Voyage of the Beagle (QH11.D2
Wheldon; online at
http://www.literature.org/authors/darwincharles/the-voyage-of-the-beagle/index.html).
• During his voyage, Darwin read Charles Lyell’s
(1797-1875) Principles of Geology, which
indicated that the Earth is old and has been formed
by geological processes still at work today.
Evolution: history of an idea, V
• Darwin came up with his idea of “descent with
modification” through the process of natural
selection soon after his return in 1836, but was
reluctant to publish, until spurred to do so by
hearing that A.R. Wallace (1822-1903), a
naturalist/collector working in Indonesia, had come
up with similar ideas.
• On the Origin of Species by Natural Selection was
first published in 1859, and shook the scientific and
religious world of the 1860s (online as
http://www.bookrags.com/books/otoos/index.htm).
Darwinian Evolution
Darwin’s theory has two main parts:
1. Individuals vary, and species evolve as they
accumulate differences from their ancestors. All
living things are related through evolution to
common ancestors.
2. The force driving evolution is natural selection
(which can be mimicked by artificial selection),
which causes individuals with features for success to
replace those lacking them. This is differential
reproduction: adapted individuals leave more
descendants than those that are not adapted (to the
particular environment where they live).
Fossils provide a lot of evidence
in support of evolution.
Fossils may be compressed or embedded remains,
petrified (mineralized), or recorded as imprints
or casts
• Many fossil species are clearly extinct – they
do not exist today. Some are very close to
existing species – fossils in western Canada of
ginkgos and tulip trees that resemble modern
Chinese ginkgo and tulip trees of China and
eastern U.S.
Fossils, II
2. Fossils appear in historical sequence from
simplest to more complex, and in a sequence
of major groups: among vertebrates, from
fish, then amphibians, reptiles, mammals,
dinosaurs and then birds; among vascular
plants, first spore-bearing, then
gymnosperms, then angiosperms.
3. Fossils also provide missing links between
different groups that are present today:
whales with legs, showing their evolution
from land mammals.
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Other lines of support for
evolution:
Biogeography
Comparative anatomy
Comparative embryology
Physiology
Molecular biology
Related organisms share groups of derived
characters that arose in their common
ancestors.
A brief geological history of Earth
• 4 Eras, 11 Periods, [9 Epochs] to remember
• P_____________ P____________ C____________
O_____________ S___________ D_____________
C____________ M_____________ P____________
P_____________ M____________ T____________
J______________ C______________
C______________ T_____________ P____________
E______________ O____________ M____________
P____________ Q_____________
P________________ H______________
Geological Time Scale I
• Precambrian (4500 - 570 MYA)
• Paleozoic (570-245 MYA)
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Cambrian (570-510 MYA)
Ordovician (510-439 MYA)
Silurian (439-408 MYA)
Devonian (408-362 MYA)
Carboniferous (362-290 MYA)
• Mississippian (362-322)
• Pennsylvanian (322-290)
– Permian (290-245 MYA)
Geological Time Scale II
• Mesozoic (245-65 MYA)
Triassic (245-208 MYA)
– Jurassic (208-145 MYA)
– Cretaceous (145-65 MYA)
–
• Cenozoic (65 MYA - present)
–
Tertiary (65-1.6 MYA)
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Paleocene (65-56)
Eocene
Oligocene
Miocene
Pliocene
Quaternary (1.6 MYA - present)
• Pleistocene (1.6-0.01 MYA)
• Holocene = Recent (10,000 YA - present)
Brief history of life on Earth
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Let’s start from the beginning:
Precambrian (4500-570 MYA) big extinction 580 MYA
Earth formed 4.5-4.6 BYA
Life originated at least 3.5 BYA - more than likely
heterotrophs feeding on simple carbohydrates [possibly
3.85 BYA, but extinguished by a meteor bombardment
and re-established, survived in refuge, or “reintroduced”
from outer space?]
Phototrophs originated 3.4 BYA
Eukaryotes originated (more than once) at least 1.5 BYA
Multicellular animals by 700 MYA (and probably
multicellular “protists” too)
Fungi originated at least 600 MYA
Brief history of life on Earth, II
• Paleozoic (570-245 MYA)
– Cambrian (570-510 MYA) “Explosive evolution” of phyla,
including chordates
– Ordovician (510-439 MYA) Major extinction event, possible
invasion of land by plants
– Silurian (439-408 MYA) Major extinction event, first fossil
plants
– Devonian (408-362 MYA) Diversification of land plants,
appearance of insects, extinction of primitive land plants, first
vascular plants 400 MYA
– Carboniferous (362-290 MYA) “Coal Age” – age of sporebearing vascular plants
– Permian (290-245 MYA) Origin of conifers, cycads, ginkgos
and replace forests of horsetails and lycopods; ends with major
extinction event; 1st vessels 260 MYA
Brief history of life on Earth, III
• Mesozoic (245-65 MYA)
– Triassic (245-208 MYA) Forests of gymnosperms and ferns;
first dinosaurs and first mammals
– Jurassic (208-145 MYA) Vegetation dominated by cycads and
other gymnosperms
– Cretaceous (145-65 MYA) Angiosperms appear [as fossils]
and diversify, become dominant; “age of reptiles”, ends with
extinction of dinosaurs (and many other groups)
• Cenozoic (65 MYA – present)
– All major groups of present-day plants have appeared;
angiosperms continue to dominate and diversify, with centers
of diversity based on origins and distributions at least partly
based on past continental connections (continental drift =
plate tectonics)
Plate Tectonics
• Close examination of a globe often results in
the observation that most of the continents
seem to fit together like a puzzle: the west
African coastline seems to snuggle nicely into
the east coast of South America and the
Caribbean sea; and a similar fit appears across
the Pacific. The fit is even more striking
when the submerged continental shelves are
compared rather than the coastlines.
Plate Tectonics, II
• In 1912 Alfred Wegener (1880-1930) noticed the same
thing and proposed that the continents were once
compressed into a single protocontinent which he
called Pangaea (meaning "all lands"), and over time
they have drifted apart into their current distribution.
He believed that Pangaea was intact until the late
Carboniferous period, about 300 million years ago,
when it began to break up and drift apart
[actually a little later – end of Permian
~250 MYA]
Plate Tectonics, III
• Not until the 1960's and the discoveries of
features like mid-oceanic ridges, geomagnetic
anomalies parallel to the mid-oceanic ridges,
and the association of island arcs and oceanic
trenches occurring together and near the
continental margins, suggested convection
might indeed be at work. These discoveries and
more led Harry Hess (1962) and R. Deitz (1961)
to publish similar hypotheses based on mantle
convection currents, now known as "sea floor
spreading".
How does this impact the
evolution of plants?
• [Good exam question, particularly for the
final exam]