Transcript Chapter 25 The History of Life on Earth

The History of Life on Earth
Chapter 25
Objectives
 Conditions that led to origin of life on earth
 The history of life as seen in fossils
 Key events include origin of single-cellular and multi-
cellular organisms and the development of terrestrial
life
 The effects of continental drift, mass extinctions, and
adaptive radiation on groups of animals
 Developmental genes can radically change body
forms
 Understand why evolution is NOT goal oriented.
Early earth




Abiotic synthesis of amino acids and
nucleotides
Formation of macrocmolecules (proteins and
nucleic acids)
Packaging these molecules into protobionts
Origin of self replicating molecules that led to
inheritance
Synthesis of organic compounds
 Oparin-Haldane hypothesis—Early earth was
a reducing atmosphere that led to synthesis
 Miller and Urey tested the hypothesis which
yielded amino acids


Demonstrated that abiotic synthesis was
possible
Analysis of meteorites show presence of AAs
 Synthesis of macromolecules may have been
initiated by formation of AA polymers
Protobionts
 Protobionts are abiotically created
molecules surrounded by a
membrane.


They can engage in simple
reproduction and metabolism
The can maintain an internal
environment different than the external
environment.
 Liposomes can spontaneously
organize in water from lipids and
organic molecules
Self replicating RNA
 RNA catalysts are called ribozymes
 Protobionts with RNA were more successful
 The development of DNA provided a more
stable molecule for genetic information
Key events in earth’s history
The First Eukaryote
The First Eukaryote
Origin of multicellularity
 First evidence of
multicellular organisms
(algae) ~1.2 billion years
 The fossil record
indicates that the first
major diversification of
multicellularity was after a
thaw ~565 million years

Ediacaran biota
 The Cambrian explosion
Colonization of land ~ 500 mya
 Adaptations developed to live on land



Plants produced waterproof coating and a
vascular system for internal transport
Early plants had no roots or leaves
Fungi followed plants
 Arthropods are the most abundant land
animals
 Tetrapods arrived ~365mya

Our species arrived 195,000 years ago
Rise and fall of organisms
 Continental drift


Formation of mountains
Oceanic plates usually slide below terrestrial
plates
Continental drift
 Alters habitats
 Reroutes ocean currents
 Changes weather patterns
 Promotes allopatric
speciation
 Helps explain why fossils
in two different regions
can be the same
Mass Extinctions
Permian
extinction
Cretaceous
extinction
Cretaceous extinction
Consequences of mass extinctions
 Evolutionary lineages disappear
 Reduction in the diversity of an ecosystems
 Increase in predators
 Arising of adaptive radiations
Mass extinction and predators
Adaptive radiation
 An organism’s movement into a variety of
different environments or exploitation of a
variety of different food sources leads to
adaptive radiation.
 The mass extinction of dinosaurs gave way to
adaptive radiation of mammals 65 million
years ago.
Mammalian adaptive radiation
The Silversword
Alliance
Dubautia laxa
KAUAI
5.1
million
years
1.3
million
years
MOLOKAI
MAUI
OAHU
3.7 LANAI
million
years
Argyroxiphium sandwicense
HAWAII
0.4
million
years
Dubautia waialealae
Dubautia scabra
Dubautia linearis
Exaption
 Using a trait that evolved for one purpose for
another purpose.
 The lightweight honeycombed bones of early
non-flying birds were taken advantage of by
birds that fly.
 Feathers were initially developed for
camouflage, courtship, or thermoregulation.
Later they developed for flight.
 Karel Liem, “Evolution is like modifying a
machine while it is running.”
Evo-devo
 Genes that control development have had a
profound effect on evolution



Effect growth rates of particular body parts
Controls timing of the emergence of particular
structures
Controls spatial pattern of particular structures
Evolution and development
 Genes control the rate, timing, and spatial
pattern of development.
Evolution and development
 Varying the
rate of growth
of different
body regions
leads to
morphological
changes.
Heterochrony and
salamanders
 Foot growth gets
turned off later in
ground dwelling
salamanders.
 Paedomorphosis
Changes in spatial pattern
 Homeotic
genes, such as
Hox genes
control spatial
organization of
body features.
Chicken leg bud
Region of
Hox gene
expression
Zebrafish fin bud
Hypothetical vertebrate
ancestor (invertebrate)
with a single Hox cluster
First Hox
duplication
Hypothetical early
vertebrates (jawless)
with two Hox clusters
Second Hox
duplication
Vertebrates (with jaws)
with four Hox clusters
New developmental genes
Gene regulation
Evolved
complexity
Mollusc eye
evolution
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Patch of pigmented cells
Eyecup
Slit shell Pleurotomania
Limpet Patella
Fluid-filled cavity
Epithelium
Optic
nerve
Nerve fibers
Cellular
fluid
(lens)
Pigmented
layer (retina)
Pinhole camera-type eye
Nautilus
Optic nerve
Eye with primitive lens
Marine snail Murex
Cornea
Lens
Retina
Optic nerve
Complex camera-type eye
Cornea
Squid Loligo
Recent
Equus
Hippidion and other genera
Pleistocene
Nannippus
Pliohippus
Hipparion Neohipparion
Pliocene
Sinohippus
Megahippus
Callippus
Archaeohippus
Merychippus
Miocene
Anchitherium
Hypohippus
Parahippus
Miohippus
Oligocene
Mesohippus
Paleotherium
Epihippus
Propalaeotherium
Eocene
Pachynolophus
Orohippus
Key
Hyracotherium
Grazers
Browsers