Aucun titre de diapositive

1
(No Transcript)
2
Cyanobacteria
Origin of life ?
Precambrian
Cambrian
ENS Cachan 2007
3
Stages in the Evolution of the Earths Atmosphere
Stage I

• Primitive Atmosphere
• 4.4 4.0 billion years ago with a time span of
  one million years
• A reducing atmosphere primarily consisting of
  H2 and He, with trace levels of CO, CH4, H2O (v),
  N2, H2S, NH3, HCl, Ar, and HCN
• Lighter gases (H2 and He) escaped to space
• CH4 à CO à CO2 (oxidation)
• 2NH3 hn à N2 2H2

ENS Cachan 2007
4
Stages in the Evolution of the Earths Atmosphere
Stage II

• Secondary Atmosphere 4.0 to 3.3 billion years
  ago
• H2O, N2, and CO2 predominant constituents, with
  trace levels of CO, SO2, Ar, He
• Cooling of earth resulted in condensation of
  water vapor and the appearance of oceans (3.8
  billion years ago)
• Water soluble gases (CO2, SO2, HCl) dissolved in
  the primitive ocean
• Appearance of chemosynthetic bacteria about 3.5
  bya
• First appearance of Oxygen (O2) in the prebiotic
  atmosphere

5
The First Signs of Life(- 4/3.5 billion years)

• The oldest living prokaryotes is a group of
  bacteria that survive by obtaining energy from
  sulfur compounds (still live today!)

Some ancient form of photosynthesis
different from modern plants They probably used
hydrogen sulfide (H2S) whereas modern ones use
water (H2O)
ENS Cachan 2007
6
Stages in the Evolution of the Earths Atmosphere
Stage III

• Living Atmosphere 3.3 bya to present
• Accumulation of O2 to its present day atmospheric
  level of 21 as early as 430 million years ago
• Development of the ozone layer responsible for
  shielding the earths surface from UV rays
• O2 O M à O3 M
• Evolution of several new biochemical pathways
  significant to the global biogeochemical cycles,
  e.g., nitrification

ENS Cachan 2007
7
The Way Towards Modern Organisms

• The first great change occurred roughly 3
  billion years ago, when a more modern form of
  photosynthesis evolved
• It substituted H2O for H2S in their metabolic
  pathways
• Why was this important?

Production of molecular oxygen
Production of ozone
Other events?
ENS Cachan 2007
8
Cyanobacteria fossils(- 3 billions years)
ENS Cachan 2007
9
Origin of Life

• Stanley Miller and Harold Urey (1953)
• early experiment with primitive atmosphere
• included methane, hydrogen, water vapor, ammonia
  in reaction vessel and added energy
• products synthesized include
• alanine
• glycine
• glutamic acid
• aspartic acid
• other organic compounds urea, lactic acid,
  acetic acid

• Later research has produced 18 of 20 amino
  acids,
• purines, pyrimidines, sugars, etc. by similar
  techniques

ENS Cachan 2007
10
Possible Sources of Lifes Origin(S. Miller, H.
Urey1953)

• A hot reducing environment
• High temperatures
• H2O, CO2, N2
• H2S, CH4, NH3, H2
• NO, O2

ENS Cachan 2005
11
Living organisms are classified as

• Prokaryotes
• have genetic material, but not organized into a
  defined nucleus, i.e. no nuclear membrane
• Genetic material consists of a single molecule of
  nucleic acid (usually circular DNA molecule)
• Do not have organized chloroplasts or
  mitochondria
• examples bacteria, cyanobacteria (blue-green
  algae)
• Eukaryotes
• Presence of a distinct nucleus with a nuclear
  membrane
• have organized chloroplasts and mitochondria
• genetic material organized into structures called
  chromosomes.

ENS Cachan 2007
12
Prokaryote vs Eukaryote
Prokaryote No nucleus Single coiled chromosome
with few associated proteins Bacterial cell
wall No organelles 17s RNA
Eukaryote DNA in nucleus Chromosomes with many
proteins (histones) No cell wall Organelles
(mitochondria, chloroplasts) 18s RNA
13
The Tree of life
Common ancestor

• Archaebacteria (halophiles, methanogens and
  thermophiles
• living in hostile, anoxic conditions).
• Eubacteria (e.g. purple/green bacteria,
  cyanobacteria)
• the first true photosynthesisers.
• Eukarya

14
THE LIFE TO DAY RICHNESS AND DIVERSITY
15
THE LIVING SPECIES
How many species are on the earth ?
difficult to answer
Estimates of the total number of living species
from 10 to 100 million !!
likely the actual number is on the order of 13
to 14 million
Nearly 2/3 of these are insects !
ENS Cachan 2007
Species Richness
16
CLASSIFY LIVING ORGANISMS
One of the most important 18th century
naturalists was a Swedish botanist and medical
doctor He wrote 180 books mainly describing
plant species in extreme detail.
Karl Linne 1707-1778
ORDER FAMILY
FAMILY GENUS GENUS
GENUS GENUS SPECIES
SPECIES SPECIES SPECIES SPECIES SPECIES
SPECIES SPECIES
ENS Cachan 2007
17
Linnaean taxonomic hierarchy
( Ex Homo sapiens)
Domain Eukaryota All nucleated
organisms Kingdom Metazoa All animals Phylum Ch
ordata All animals with backbone Class Mammalia W
arm-blooded milk-producing vertebrates Order Prim
ates Monkeys (Super)Family Hominoidea Genus Hom
o Species sapiens Other spp. (e.g. habilis,
erectus, extinct)
ENS Cachan 2007
18
(No Transcript)
19
Platyhelminthes (flatworms, tapeworms, flukes)
Mollusca (snails, clams, squid)
Annelida (worms, leeches)
Echinodermata (starfish, sea-urchins,
sea-cucumbers)
Chordata (fish, amphibians, reptiles, birds,
mammals)
Arthropoda (insects, crustaceans, millipedes)
20
Measuring Biodiversity

• Species Richness the total number of given
  species in a quantified area.
• Species Evenness the degree to which the number
  of individual organisms are evenly divided
  between different species of the community.

21
Measuring Biodiversity

• Disparity measures the phenotypic differences
  among species resulting from the differences
  genes within a population.
• Species Rarity the rarity of individual
  organisms within a quantified area.

http//www.rit.edu/rhrsbi/GalapagosPages/DarwinFi
nch.html
22
Biodiversity Species-area curves

• The number of species found depends (typically as
  a power law linear on a log-log plot) on the
  size of the area sampled
• Applies on many scales, local to global
• Design of nature reserves/estimates of
  biodiversity

23
BIODIVERSITY GENETIC DIVERSITY
Genetic variation arises through two processes
mutation and recombination Mutation
occurs when DNA is imperfectly copied during
replication, leading to a difference between a
parent's gene and that of its offspring. Some
mutations affect only one bit in the DNA others
produce rearrangements of large blocks of DNA.
Recombination occurs when genes from two parents
are shuffled to produce an offspring, as happens
regularly in sexual reproduction. Usually the two
parents belong to the same species, but sometimes
(especially in bacteria) genes move between
more distantly related organisms.
24
FROM THE COMMON ANCESTOR UNTIL NOW THE
EVOLUTION THEORY
25
First dinausaurs
Major ecological changes
increased complexity 500 millions of years
ENS Cachan 2006
26
Lamarckian Evolution

• Published Philosophie Zoologique, 1809
• Inheritance of acquired characteristics i.e.
  Phenotypic changes, passed to successive
  generations
• Example long legs and webbed feet of wading
  birds
• Clearly a theory formulated in ignorance of
  genetic principles

• Jean Baptiste
• Lamarck
• 1744-1829

ENS Cachan 2007
27
Darwinian Evolution

• Published The Origin of Species, 1859
• Acquired characteristics are not inherited by
  offspring
• Evolution by natural selection mutations in
  genotype, selection on phenotype
• Theory has survived (though much has been added)
  because of basic foresight into correct genetic
  principles

ENS Cachan 2007
28
The Darwin trip to Galapagos
ENS Cachan 2007
29
(No Transcript)
30
Adaptation
The beaks of the Finches are adapted to different
jobs in the same way as tools.
31
Micro-evolution
Macro-evolution

• The origin of taxonomic groups higher than the
  species level.

• A change in a populations gene pool over a
  sucession of generations.
• Evolutionary changes in species over relatively
  brief periods of geological time.

ENS Cachan 2007
32
(No Transcript)
33
Micro-evolution
Five Mechanisms of Micro-evolution

• 1. Genetic drift
• Change in the gene pool of a small population
  due to chance.

2. Gene Flow The gain or loss of alleles
from a population by the movement of individuals
(Immigration or emigration).
3. Mutation Change in an organisms DNA that
creates a new allele. 4. Non-random
mating The selection of mates other than by
chance. 5. Natural selection Differential
reproduction.
ENS Cachan 2007
34
Example of Macro-evolution
unusually complete fossil record of horses
4
4
- 60 My
-3 My Today
Eocene
Flexible
35
Whale Evolution Based on the Fossil Record
55 mya
Mesonychids (extinct land mammals, with
whale-like teeth)
48 mya
Ambulocetus natans Walked on land. Swam with
backbone and hindlimbs
Rodhocetus kasrani Spent little time on land
46 mya
Modern Whale
36
The Baldwin Effect

• Discovered independently by Morgan, Osborn, and
  Baldwin in 1896
• Suggested that an individuals lifetime learning
  can guide evolution

James Mark Baldwin 1861-1934
The Baldwin effect concerns the trade-offs
(the costs and benefits) of learning, in the
context of evolution.
37
The Baldwin Effect

• Suppose a population of plastic individuals
• encounters a new environment in which phenotype X
  is
• necessary for survival.
• Only those whose heritable plasticity encom-
• passes X are able to acquire X and thereby
  survive.
• There is no direct transmission of X, only
• transmission of heritable factors determining the
  range of
• plasticity.
• Any new heritable variants that more directly
• determine X, (i.e., variants that are less
  plastic and
• include X within the range of phenotypic
  possibility) are
• favored by natural selection. Any variants that
  heritably
• determine only nonoptimal phenotypes are weeded
  out.
• Ultimately a heritable variant that
  directlyproduces X will fix
• in the population.

38
Evidence of Evolution

• 1. Biogeography
• Geographical distribution of species.
• 2. Fossil Record
• Fossils and the order in which they appear in
  layers of sedimentary rock (strongest evidence).

39
Evidence of Evolution (2)

• 3. Taxonomy
• Classification of life forms.
• 4. Homologous structures
• Structures that are similar because of common
  ancestry (comparative anatomy)

40
Evidence of Evolution (3)

• 5. Comparative embryology
• Study of structures that appear during
  embryonic development.
• 6. Molecular biology
• DNA and proteins (amino acids)

41
(No Transcript)
42
INTELLIGENT DESIGN
The theory of intelligent design (ID) holds that
certain features of the universe and of living
things are best explained by an intelligent cause
rather than an undirected process such as natural
selection.
Intelligent Design is an intellectual movement
that includes a scientific research program for
investigating intelligent causesand that
challenges naturalistic explanations of origins
which currently drive science education and
research.
43
(No Transcript)
44
Tree based on cytochrome c sequence
ENS Cachan 2007