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

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

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

The Fossil Record: Evidences

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

àThe 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

The Fossil Record: Evidences

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

The Fossil Record: Evidences

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!

The key ideas from studies of fossils Evidences

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

The Biochemical Evidence Evidences

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

The Biochemical Evidence Evidences

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 àIt perhaps once served as an important part of the digestive system but no longer needed. (Darwin suggested it as a organ for digesting leaves)

Vestigial Organs Evidences

3. Numerous vestigial organs have been recognized Penguin’s wings Whale’s tiny internal legs Human’s?

Vestigial Organs Evidences

3. Numerous vestigial organs have been recognized Penguin’s wings Whale’s tiny internal legs Human’s? Appendix Coccyx (tailbone) Wisdom teeth . . .

Vestigial Organs Evidences

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! èèNatural 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

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 èè 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

Natural Selection

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

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

Mass Extinctions and the Rate of Evolution

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