1. Chapter 25 continued

2. Homework 1. Lab write up extended for Friday
2. Read and outline pp 521 (beginning with Mass Extinctions) to 530
Chapter 25 outline will be checked for completion grade tomorrow
3. Quiz tomorrow on Chapter 25 on:
Hypotheses for origin of life on Earth, the sequence of stages for life on earth, adaptive radiation, and section 25.5

3. Concept 25.1: Conditions on early Earth made the origin of life possible
Hypothesis: Chemical and physical processes on early Earth may have produced very simple cells through a sequence of stages:
1. Abiotic synthesis of small organic molecules
2. Joining of these small molecules into macromolecules
3. Packaging of molecules into protocells
4. Origin of self-replicating molecules

4. Meso- Cenozoic zoic Paleozoic Humans Colonization of land
Figure
Meso-
zoic
Cenozoic
Humans
Paleozoic
Colonization
of land
Origin of solar
system and
Earth
Animals
Multicellular
eukaryotes 1 4
Figure 25.7 Clock analogy for some key events in Earth’s history.
Proterozoic
Archaean B o i l g l i a o n s s a r 2 of y e 3
Prokaryotes
Single-celled
eukaryotes
Atmospheric oxygen

5. How Rocks and Fossils Are Dated
Sedimentary strata reveal the relative ages of fossils
The absolute ages of fossils can be determined by radiometric dating
A “parent” isotope decays to a “daughter” isotope at a constant rate
Each isotope has a known half-life, the time required for half the parent isotope to decay

7. 25.4 Mass Extinctions
The fossil record shows that most species that have ever lived are now extinct
caused by changes to a species’ environment
At times, the rate of extinction has increased dramatically and caused a mass extinction
The result of disruptive global environmental changes

8. The “Big Five” Mass Extinction Events
Five mass extinctions documented in fossil records over the past 500 million years
In each of the five mass extinction events, more than 50% of Earth’s species became extinct

9. (families per million years):
Figure 25.15
1,100 25
1,000
900 20
800
700 15
600
(families per million years):
Total extinction rate
Number of families:
500 10
400
300 5
200
Figure Mass extinction and the diversity of life.
100
Era
Paleozoic
Mesozoic
Cenozoic Q
Period E O S D C P Tr J C P N
542
488
444
416
359
299
251
200
145
65.5
Permian
Cretaceous

10. The Permian mass extinction occurred in less than 5 million years and caused the extinction of about 96% of marine animal species

11. A number of factors might have contributed to these extinctions
Intense volcanism in what is now Siberia
Global warming resulting from the emission of large amounts of CO2 from the volcanoes
Reduced temperature gradient from equator to poles
Oceanic anoxia from reduced mixing of ocean waters

12. The Cretaceous mass extinction 65
The Cretaceous mass extinction million years ago separates the Mesozoic from the Cenozoic
Organisms that went extinct include about half of all marine species and many terrestrial plants and animals, including most dinosaurs

13. Consequences of Mass Extinctions
1. Mass extinction can alter ecological communities and the niches available to organisms
2. It can take from 5 to 100 million years for diversity to recover following a mass extinction
3. The percentage of marine organisms that were predators increased after the Permian and Cretaceous mass extinctions
4. Mass extinction can pave the way for adaptive radiations

14. Adaptive Radiations
Adaptive radiation is the evolution of diversely adapted species from a common ancestor
Organismal groups form many new species with adaptations specific for different niches
Adaptive radiations may follow
Mass extinctions
The evolution of novel characteristics
The colonization of new regions

15. Worldwide Adaptive Radiations
Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs
The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size
Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects, and tetrapods

16. Close North American relative, the tarweed Carlquistia muirii
Figure 25.20
Close North American relative,
the tarweed Carlquistia muirii
Dubautia laxa
KAUAI
5.1
million
years
MOLOKAI
1.3
million
years
Argyroxiphium
sandwicense
OAHU
3.7
million
years
LANAI
MAUI N
HAWAII
0.4
million
years
Figure Adaptive radiation on the Hawaiian Islands.
Dubautia waialealae
Dubautia scabra
Dubautia linearis

17. KAUAI 5.1 million years MOLOKAI 1.3 million OAHU years 3.7 million
Figure 25.20a
KAUAI
5.1
million
years
MOLOKAI
1.3
million
years
OAHU
3.7
million
years
MAUI
LANAI N
HAWAII
Figure Adaptive radiation on the Hawaiian Islands.
0.4
million
years

18. 25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes
Small genetic changes can cause major morphological differences between species
EX: Japanese Euhadra snails, the direction of shell spiral affects mating and is controlled by a single gene

19. 25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes
Heterochrony- evolutionary change in rate/timing of developmental events
Organismal shape depends on relative growth rates of different body parts
Example: skeletal structure for bat rings results from increased growth rates of finger bones

20. 25.5 Major changes in body form can result from changes in sequences and regulation of developmental genes
Altering homeotic genes could lead to major evolutionary changes
These genes control the placement and arrangement of body parts
Example: Hox genes, class of genes that instruct cells in a particular location to develop into the correct body structure

21. Hox gene 6 Hox gene 7 Hox gene 8 Ubx About 400 mya Drosophila Artemia
Figure 25.24
Hox gene 6
Hox gene 7
Hox gene 8
Ubx
About 400 mya
Figure Origin of the insect body plan.
Drosophila
Artemia

22. Changes in Gene Regulation
Changes in morphology likely result from changes in the regulation of developmental genes rather than changes in the sequence of developmental genes
Ex: threespine sticklebacks in lakes have fewer spines than their marine relatives

23. Concept 25.6: Evolution is not goal oriented
Evolution is like tinkering—it is a process in which new forms arise by the slight modification of existing forms
It is simply the change in allele frequencies, or genetic composition, in populations from generation to generation
Evolution can be random or adaptive, in which case, individuals adapt to their specific environment

24. Evolutionary Novelties
These structures that evolve to have a new function or have evolved from simple to complex structures
Ex: simple to complex eyes

25. (a) Patch of pigmented cells (b) Eyecup
Figure 25.26
(a) Patch of pigmented cells
(b) Eyecup
Pigmented cells
(photoreceptors)
Pigmented
cells
Epithelium
Nerve fibers
Nerve fibers
(c) Pinhole camera-type eye
(d) Eye with primitive lens
(e) Complex camera lens-type eye
Epithelium
Cornea
Cellular
mass
(lens)
Fluid-filled
cavity
Cornea
Lens
Figure A range of eye complexity among molluscs.
Retina
Optic nerve
Optic
nerve
Optic nerve
Pigmented
layer
(retina)