From Tree Shrew to Ape (9).docx

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Published on 13 Apr 2013
School
McMaster University
Department
Biology
Course
BIOLOGY 1M03
Professor
Page:
of 11
Chapter 9 From Tree Shrew to Ape 3/16/2013 3:44:00 PM
o Extinction of the dinosaurs at the beginning of the Cenozoic Era was coupled with the
radiation of mammals
Modern descendants from this radiation (eg. horses, bats, whales, primates) evolved
from a creature that looked like the contemporary shrew
o Darwin’s theory complex adaptions are assembled gradually
Each step favoured by natural selection
Human adaptations: grasping hands, bipedalism, tool-making abilities, language, and
large-scale cooperation
Continental Drift and Climate Change
o Scenery has changed along with evolution of organisms
o Climate influences our interpretations of fossil records
o What is adaptive in one environment may not be adaptive in another
o If the environment had not changed, adaptations in human evolution would have been
steady improvements towards human perfection
ie. evolution would progress towards a fixed goal
o Since the environment has changed over time, changes reflect adaptations to changing
environmental conditions
o The world has become much colder and drier in the last 20 million years; particularly
variable in the last 800,000 years
If climate had remained warmer, human ancestors would have remained in safety of
trees and would not have become terrestrial or bipedal
o Continental drift movement of continents
o ~200 mya, all of the land making up present day continents were joined together in a single
large landmass: Pangaea
o ~150 mya, Pangaea began to break apart
Northern half: Laurasia (included present North America & Eurasia (minus India))
Southern half: Gondwanaland (rest of the land)
By the time dinosaurs became extinct (65 mya), Gondwanaland had broken up
o Africa and India separated; India headed north eventually crashing into
Eurasia
o Remainder of Gondwanaland stayed south eventually breaking up into South
America, Antarctica and Australia
o ~5 mya South America drifted north to join North America
o Importance of continental drift:
1. Oceans serve as barriers that isolate certain species from others position of
continents play an important role in evolution of species
The long isolation of South America creaes one of the biggest puzzles in our
knowledge of primate evolution
2. Continental drift is one of the engines of climate change
Climate fundamentally influences human evolution
o The size and orientation of the continents have important effects on climate
Very large continents tend to have severe weather
Pangaea was very large and likely had very cold weather in the winter
The period peak of warmth in Miocene era allowed palm trees to grow as far north as
present-day Alaska, and only the tallest peaks in Antarctica were glaciated
Chapter 9 From Tree Shrew to Ape 3/16/2013 3:44:00 PM
The Methods of Paleontology
o Certain geological settings allow the bones of dead organisms to be preserved long enough
for the organic material in the bones to be replaced by minerals (mineralized) from the
surrounding rock
These natural copies of bones are called fossils
Paleontologists scientists who recover, describe, and interpret fossil remains
o Studying the shapes of different bones tells us what early hominins were like
Their size, diet, where they lived, how they moved, and a bit about how they lived
Can tell us something about the phylogenetic history of long-extinct creatures
o The kinds of plant and anima fossils found in association with the fossils of our ancestors tell
us what the environment was like (eg. forested or open, rainfall)
o Radiometric methods one of the most important ways to date fossils
Isotopes forms of the same element with different numbers of neutrons in their
nucleus
Based on the fact that the isotopes of certain elements are unstable
o Ie. they change from one isotope to another of the same element of to an
entirely different element
o Eg. C14 changes to N14 and K40 changes spontaneously to Ar40
Radioactive decay occurs at a constant, clocklike rate that can be measured
o Different Radiometric Methods:
1. Potassium-argon dating
Used to date the age of volcanic rocks found in association with fossil material
All argon is boiled out of molten rocks due to high temperatures of volcanoes
Any argon present in a volcanic rock must be due to potassium decay
If a fossil is found in a geological stratum lying under the stratum that contains
the volcanic rock, then the fossil is surely older than the rock
New variant of technique: argon-argon dating. The potassium in the sample is
converted to an isotope of argon before it is measured; more accurate
2. Carbon-14 dating (Radiocarbon dating)
Based on an unstable isotope of carbon that living animals and plants
incorporate into their cells
When alive, ratio of unstable to stable isotope is the same as in atmosphere
When dead, C14 starts to decay into N14 at a constant rate
3. Thermoluminescence dating
Based on the effect of high energy nuclear particles travelling through rock

Document Summary

3/16/2013 3:44:00 pm: extinction of the dinosaurs at the beginning of the cenozoic era was coupled with the radiation of mammals. Modern descendants from this radiation (eg. horses, bats, whales, primates) evolved from a creature that looked like the contemporary shrew: darwin"s theory complex adaptions are assembled gradually. Human adaptations: grasping hands, bipedalism, tool-making abilities, language, and large-scale cooperation. Continental drift and climate change: scenery has changed along with evolution of organisms, climate influences our interpretations of fossil records, what is adaptive in one environment may not be adaptive in another. Northern half: laurasia (included present north america & eurasia (minus india)) Southern half: gondwanaland (rest of the land) By the time dinosaurs became extinct (65 mya), gondwanaland had broken up: africa and india separated; india headed north eventually crashing into. Eurasia: remainder of gondwanaland stayed south eventually breaking up into south. America, antarctica and australia: ~5 mya south america drifted north to join north america.