natural selection. questions from biogeography biogeography is the study of patterns in the...
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Natural Selection
Questions from biogeography
Biogeography is the study of patterns in the geographic distribution of individual species and entire communities.
Questions from biogeography
Some patterns were intriguing to early scientists. Many plants and animals
are found only on islands in the middle of the ocean and other remote places.
Other species are strikingly similar and live far apart.
Rhea
Emu
Ostrich
Questions from comparative morphology
The similarities and differences among species raised questions that gave rise to comparative morphology: the study of body plans and structures among groups of organisms.
Questions from comparative morphology
Why do some organisms have useless body parts, called vestigial structures?
Questions about fossils
About the same time, geologists were mapping layers of rock exposed by erosion or quarrying.They added to the
confusion when they found fossils in the same kinds of layers in different parts of the world.
New Theories19th century naturalists found themselves trying to
reconcile the evidence of change with a traditional conceptual framework that simply did not allow for it.
George Cuvier Cuvier came up with the theory
of Catastrophism.It states that a single time of
creation had populated the world, that monstrous earthquakes, floods, and other major catastrophes did happen, and many living things died.Each time, survivors repopulated
the world. There were no new species,
naturalists simply had not yet found all the fossils that would date to the time of creation.
Georges Cuvier established extinction events as a fact and established the fields of comparative anatomy and physiology.
Problems with CuvierCharles Lyell and other
geologists were arguing, erosion and other gradual, natural processes of change had more impact on Earth history than rare catastrophes.
The idea that gradual, repetitive change had shaped Earth became known as the theory of uniformity.
Charles Lyell was a well-known and respected geologist of his time and became a close and influential friend to Charles Darwin.
Lyell’s IdeaThe theory of Uniformity bothered scholars who firmly believed that the Earth could be no more than 6,000 years old. Lyell’s calculations showed that it must have taken millions of years to sculpt the present landscape.
Jean Baptiste LamarckJean Baptiste Lamarck
thought that offspring inherit traits that a parent acquired in its lifetime.By his hypothesis,
environmental pressure and internal needs promote permanent changes in an individual’s body form and functions, which offspring then inherit.
Problems with LamarckAs Lamarck
correctly inferred, the environment is a factor in changes in the lines of descent.However, his hypothesis has not been supported by environmental tests.
Although this body builder has built his muscles during his lifetime…
His children will NOT look like this.
Voyage of the Beagle
In 1831, 22-yr-old Charles Darwin joined the crew of the Beagle, which was about to leave on a five-year voyage around the world.
Charles Darwin had 10 children. Seven lived to adulthood, the last died in 1943 at the age of 93! Pictured here is William Erasmus Darwin who died at the age of 75.
Voyage of the BeagleThe Beagle sailed first to South America to finish
mapping the coastline.During the Atlantic crossing, Darwin collected and
studies marine life.He read Principles of Geology by Charles Lyell.
He noticed diverse species in environments ranging from sandy shores of remote islands to high mountains.
Darwin, Wallace, and Natural SelectionDarwin’s observations of thousands of species in different
parts of the world helped him see how species might evolve.
We still have the fossils and other specimens that Darwin collected during his voyage, including these finches!
Old Bones and Armadillos
Darwin brought thousands of specimens with him to England.Among the
specimens were fossils of glyptodonts from Argentina. Darwin found many fossils, among
which were glyptodonts. He needed the assistance of many people to assemble and correctly identify the fossils and specimens that he collected.
Old Bones and ArmadillosOf all places on Earth, armadillos live only in the places where glyptodonts once lived.What if some of traits of
their common ancestor had changed in the line of descent that led to armadillos?Descent with modification
The Glyptodont was a large herbivore the size of a car who lived about 23-5 million years ago.The modern armadillo shares much in common with the glyptodont, but is only about 30 inches long.
Key Insight—Variation in Traits
Thomas MalthusHe said that humans run out of food, living space, and other resources because they reproduce too much.
Individuals compete with one another for dwindling resources.
Thomas Malthus wrote against popular opinion with regard to society. Most thought we would improve to a utopia-like state. He had other ideas!
Key Insight—Variation in Traits
Darwin had read Thomas Malthus and deduced that ANY population has a capacity to produce more individuals than the environment can support. Individuals of those species
were not alike in their details. They varied in size, color, and other traits.He thought that perhaps
variations in traits influence an individual’s ability to secure resources and to survive and reproduce in the environment.
Sea Stars are voracious predators but many of their eggs get eaten before they even hatch. Sea stars themselves can fall prey to king crabs, sea otters, and gulls.
Key Insight—Variation in Traits
The Galapagos Islands are separated from South America by 900 kilometers of open ocean.Nearly all the finch
species of the Galapagos live nowhere else in the world, yet they share traits with mainland species.
There are 14 main islands and 3 minor islands of the Galapagos. Some islands are desert-like, some are lush and tropical, and some are both!
Key Insight—Variation in Traits
A strong-billed finch is better at cracking open hard seeds.A drought that lasts for several years will make soft seeds harder to find.
Ecologists Peter and Rosemary Grant observed an example of natural selection acting on existing traits within a population of medium ground finches in one of the Galapagos Islands.1977—A drought reduced the amount of small, soft seeds that finches preferred.
There were plenty of large, tough shelled seeds.Because the large-beaked finches in the population were able to crack the large, tough seeds, they did not starve.
The next year, the Grants noted a big increase in large-beaked hatchlings.Most of the finches with small beaks had died.
Natural Selection Defined
1. Traits vary from individual to individual of a species.
2. Some traits prove better at helping individuals compete for resources, survive, and reproduce
3. Traits are inherited.4. In time, these traits become more
frequent in the population.oThese traits can lead to an increase in fitness—an individuals ability to reproduce and pass on traits.
Natural Selection Defined.
Darwin’s HesitationDarwin wanted his theories to be
as solid as possible. He wrote his theory out, but didn’t publish for 10 years, afraid of the backlash.
Alfred WallaceHe noticed the same patterns as
Darwin. In 1858, both Wallace and Darwin’s
theories were presented jointly at a scientific meeting.Darwin published On the Origin of
Species the following year.
Alfred Russel Wallace identified the Wallace Line that divides the Indonesian archipelago into two distinct parts, one in which animals closely related to those of Australia are common, and one in which the species are largely of Asian origin
Evidence For Natural Selection
Fossils—Evidence of Ancient Life
We have fossils for more than 250,000 known species.
Diggers were discovering similar rock layers and similar sequences of fossils in distant places, such as the cliffs on both sides of the English channel.a fossil record.
Ichthyosaurs appeared about 250 mya and disappeared about 90 mya and grew to about 6.6-13 feet long! They resemble modern day dolphins.
Radiometric Dating
At one time, people could assign only relative ages to fossils.For instance a fossil
embedded in a layer of rock was said to be younger than a fossil below it.
Things changed with radiometric dating.
Radiometric dating has an error factor of less than 10%.
Placing fossils in geologic time
Researchers correlate the geologic time scale with macroevolution, or major patterns, trends, and rates of change among lines of descent (lineages).
A big connectionAs geologists were
mapping vertical stacks of sedimentary rock, they noticed some patterns.
The Atlantic coasts of South America and Africa fit like jigsaw pieces.
These observations support the plate tectonic theory.
Divergences from a shared ancestor
Comparative morphology is the study of body forms and structures of major groups of organisms.
Morphological divergence When populations of species stop reproducing with each
other, their traits may begin to diverge from one another.This is called morphological divergence.
oBody parts with similar origins but used for different functions are known as homologous structures.
Morphological convergenceSome body parts of different
species have similar form and function, but evolved independently in separate lineages.
This is called morphological convergence.
oBody parts without similar origins but used for similar purposes are also known as analogous structures.
Similarities in patterns of development
Embryology, the study of embryologic development, shows that the embryos of some vertebrate lineages are alike in the early stages of development.
What Am I?
A SNAKE!
What Am I?
A GUPPY!
What Am I?
A CHICKEN!
What Am I?
A TURTLE!
What Am I?
A MOUSE!
What Am I?
A CAT!
What Am I?
A DOG!
What Am I?
A PIG!
What Am I?
A DOLPHIN!
What Am I?
A HUMAN!