Download Evolution of Life

Evolution of Life
life is constantly changing and evolving
Today’s Keywords
evolution, fossil, extinct, vestigial organ, chemical
evolution, natural selection, adaptation, mass extinction
Contents
n  Evidences for the fact of evolution
n  Two stages of life’s evolution
1. Chemical evolution – next week
2. Natural selection
n  Geological time
n  Mass extinctions and rate of evolution
Evidences for the fact of Evolution
n 
Fossil record
n 
Biochemical evidence
n 
Vestigial organs
Evidences
The Fossil Record:
Fossils show how organisms changed over vast periods of times
and adapted to various environments.
Evidences
The Fossil Record:
Fossils show how creatures changed over vast periods of times
and adapted to various environments.
1. The fossil record reveals how different organisms came to be
what they are
2. Fossils show some sequence of gradual changes in species:
the record should be complete with many thousands years of
continuous sediments
Evidences
The Fossil Record:
1. The fossil record reveals how different organisms came to be what
they are
Ex) Fossil record of horses
50Million years ago: a cat size à many intermediate forms à modern type
Evidences
The Fossil Record:
2. Fossils show some sequence of gradual changes in species: the
record should be complete with many thousands years of continuous
sediments
Ex) Trilobite三葉蟲’s eye stalk changes
àThe length of eye stalks gradually increased over 3 million years so
that they could bury themselves deeper in soft mud, and escape
primitive predatory fish
Evidences
The Fossil Record:
1. Reveals how different organisms came to be what they are
Ex) Fossil record of horses
2. Some sequence of gradual changes in species: the record should
be complete with many thousands years of continuous sediments
Ex) Trilobite三葉蟲’s eye stalk changes
n  The major drawback of the fossil record is that it is incomplete
Nevertheless, the fossil record is the first substantial evidence
that life is constantly changing and evolving
Evidences
The key ideas from studies of fossils
1. The older the rocks, the more their animal and plant fossils differ
form modern forms
2. Often the earlier forms appear to combine characteristics of later
organisms: general characteristics of the species, not specialized
structures
3. Fossils display general trends in overall complexity of form:
Ex) Invertebrates dominant era, reptiles dominant era,
mammals dominant era
à The long-term trend towards increasing complexity of forms:
Evolution!
4. The fossil record shows that most species that have lived on
Earth have died out and are now extinct: species, like individuals,
are born, live their life, and die
à Some natural mechanism must exist to produce new species as
the old disappear!
Evidences
The Biochemical Evidence
1. The DNA of each living organism represents the sum of all the
changes from the first forms of life
2. DNA changes slowly under the influence of mutation and natural
selection
à Modern human DNA is more similar to DNA of the ape that have
a common ancestor 7-8 million years ago than DNA of the reptile
that differentiated 250 million years ago
Evidences
The Biochemical Evidence 3. We can read the genetic information by comparing sequences of
amino acids along proteins as we can compare base pairs along the
DNA molecule
Ex) A protein cytochrome C which every living cell uses in its
energy metabolism is used for analyzing genetic relations
No difference between humans and chimpanzees
86% overlap in a rattlesnake
58% overlap in common yeast
Our DNA is very similar to those organisms with which we shared the
most recent ancestors è Most important pieces of evidence for
evolution
Evidences
Vestigial Organs
1. The evidence for evolution comes from considering organs
that have no use or are even harmful to the organism in which
they are found
à Vestigial organs can be explained that they once had a
function that they have no longer
2. The human appendix盲腸: No proven function in modern
human bodies, and actually a threat
àIt perhaps once served as an important part of the digestive
system but no longer needed. (Darwin suggested it as a
organ for digesting leaves)
Evidences
Vestigial Organs
3. Numerous vestigial organs have been recognized
Penguin’s wings
Whale’s tiny internal legs
Human’s?
Evidences
Vestigial Organs
3. Numerous vestigial organs have been recognized
Penguin’s wings
Whale’s tiny internal legs
Human’s?
Appendix
Coccyx (tailbone)
Wisdom teeth
.
.
.
Natural Selection
n  The natural mechanism how life developed after the first cell was
formed, in details and more precisely, introduced by Charles Darwin
(1809-1882): On the Origin of Species
n  A simple mechanism for evolving complex multicellular life-forms
from single-celled life
Natural Selection
n  Comparison with “artificial selection”
Ex) Dog breeding: humans intentionally mates dogs to produce
puppies by feeding dogs considered useful, while neglecting or
killing others
à Over long periods of time, a new variety of dog, which is different
from the one humans started with, will appear
è If humans can introduce such changes in living things, why not
nature?! Nature should be able to do the same!
èèNatural Selection
Natural Selection
n  Two basic facts for natural selection’s operation
1. Every population contains genetic diversity
:The individual members of any population possess a range of
characteristics
2. Many more individuals are born than can possibly survive
:In nature, most individuals die in infancy, before they have a
chance to reproduce
à This characteristic makes more probable for a given species to
reproduce
Natural Selection
n  Particular genes that give advantages to match with the given
environment will more likely to be passed to the next generation
è The genes are contained in DNA of selected numbers of the
population
èè In other words, the selection is based on the specific genes
which have environmental advantages
n  Adaptation: A structure, or process, or behavior that helps an
organism survive and pass on its genes
n  Natural selection provides a mechanism for a species to change its
traits corresponding to the change in the environment
n  Natural selection is neither as controlled nor as rapid as artificial
selection: long time taking process to produce gradual changes in
populations
Geological Time
n  There are several landmarks that stand out in the process of
evolution, used as boundaries in the delineation of the past times
~ 545 M years ago
Proterozoic (“before life”): Before life suddenly appeared
~ 250 M years ago
Paleozoic (“old life”): Development of many kinds of
invertebrates s.a. trilobites, and rudimentary reptiles
~ 65 M years ago
Mesozoic (“middle life”): Age of dinosaurs-major vertebrate life
~ Present:
Cenozoic (“new life”)
: Age of mammals the human appeared at the end of this era
* M year à Million years
Geological Time
n  There are several landmarks that stand out in the process of evolution were used as
boundaries in the delineation of the past times
Proterozoic (“before life”): before life suddenly appeared
Paleozoic (“old life”): development of many kinds of invertebrates
s.a. trilobites, and rudimentary reptiles
Mesozoic (“middle life”): age of dinosaurs-major vertebrate life
Cenozoic (“new life”): age of mammals the human appeared at the
end of this era
Geological Time
n  There are several landmarks that stand out in the process of evolution were used as
boundaries in the delineation of the past times
~ 545 M years ago: Proterozoic (“before life”): before life suddenly appeared
~ 250 M years ago: Paleozoic (“old life”): development of many kinds of invertebrates
s.a. trilobites, and rudimentary reptiles
~ 65 M years ago: Mesozoic (“middle life”): age of dinosaurs-major vertebrate life
~ present: Cenozoic (“new life”): age of mammals the human appeared at the
end of this era
* M year à Million years
n  Through this long and intricate process of change, the principle
of natural selection was always at work
Mass
Extinctions and the Rate of Evolution
n  Under normal circumstances, the rate of extinction seems to be 5-6
M years by 10-20 % of the species represented in the fossil record
n  Mass extinctions: Sudden extinctions of large numbers of species
by “not” normal, but rare catastrophic events in the past
- 30 to 90% of species alive at the time
- Over a period of a few tens of thousands of years, or over a
couple of days
: Too short time to be resolved by standard geological techniques
Mass
Extinctions and the Rate of Evolution
n  Best known mass extinctions
1. Some 65 M years ago (the end of Mesozoic): Dinosaurs
extinction, about 2/3 of all living species disappeared at that time
2. About 250 M years ago (the end of Paleozoic): about 80% of
existing species disappeared
3. There are five major mass extinction events are recognized
n  One of most interesting explanations for how mass extinctions
occurred is, the impact of a large asteroid: a dust cloud raised by an
big impact on the surface of Earth.
Ex) A giant crater under the seafloor near the Yucatan Peninsula
in Mexico
Mass Extinctions and the Rate of Evolution
n  Evolution is not a smooth, gradual progress through time
n  There are two extremes in the debate about the rate of evolution
- Gradualism: most changes occur as a result of the accumulation
of small adaptations
- Punctuated equilibrium: changes occur in short bursts, separated
by long periods of stability
è Probably any rate of evolution in between these two extremes
occurred at some time Quiz 1 n  The analysis of DNA issue in human tissue is called
1. genetic engineering
2. gene splicing
3. viral therapy
4. DNA fingerprinting
5. gene therapy Quiz 1 n  The analysis of DNA issue in human tissue is called
1. genetic engineering
2. gene splicing
3. viral therapy
4. DNA fingerprinting
5. gene therapy Quiz 2
n  One of the universally possessed proteins that has been analyzed extensively
for biochemical evidence for evolution is
1. DNA
2. RNA
3. cytochrome C
4. enzymal RNA
5. amino acids
Quiz 2
n  One of the universally possessed proteins that has been analyzed extensively
for biochemical evidence for evolution is
1. DNA
2. RNA
3. cytochrome C
4. enzymal RNA
5. amino acids
Quiz 3
n  Which of the following represents a vestigial organ?
1. thumb
2. appendix
3. eye
4. stomach
5. elbow
Quiz 3
n  Which of the following represents a vestigial organ?
1. thumb
2. appendix
3. eye
4. stomach
5. elbow
Quiz 4
n  Dinosaurs disappeared approximately
1. 50 million years ago
2. 65 million years ago
3. 100 million years ago
4. 200 million years ago
5. 250 million years ago
Quiz 4
n  Dinosaurs disappeared approximately
1. 50 million years ago
2. 65 million years ago
3. 100 million years ago
4. 200 million years ago
5. 250 million years ago
Next lecture is on,
Mystery of Life: the rest part of Chapter 18
www.sci.hokudai.ac.jp/~epark/ekpark_e.html
Group-discussion day
on July 20