Principles of Science

1. Chapter 17:
The Evolution of Life
Principles of Science II

2. This lecture will help you understand:
• The Origin of Life
• Did Life on Earth Originate on Mars?
• Early Life on Earth
• Charles Darwin and The Origin of Species
• How Natural Selection Works
• Adaptation
• Staying Warm and Keeping Cool
• Evolution and Genetics
• How Species Form
• Evidence of Evolution
• Fossils: Earth's Tangible Evidence of Evolution
• The Evolution of Humans
• History of Science: The Peppered Moth
• Science and Society: Antibiotic-Resistant Bacteria

3. The Origin of Life
• For thousands of years, people believed that life
was created through spontaneous generation, the
sudden emergence of living organisms from
nonliving materials.

4. The Origin of Life
• Louis Pasteur demonstrated that life did not arise
from nonlife.

5. The Origin of Life
• Life originated billions of years ago on a young
Earth very different from the Earth of today.
• The Miller and Urey experiment modeled the young
Earth's atmosphere and
oceans.
• When Miller and Urey shot
electric sparks through the model
to simulate lightning, complex
organic molecules formed.

6. The Origin of Life
• There are two alternative hypotheses for the origin
of organic molecules on Earth:
– Organic molecules came to Earth on incoming
meteorites.
– Organic molecules were synthesized in deep-
sea environments.
• But, how do you get from organic molecules to
cells?

7. The Origin of Life
• Liposomes form spontaneously when certain lipids
are added to water. Liposomes
– have double membranes similar to cell
membranes.
– can grow, shrink, and divide.
– run chemical reactions
inside their membranes.
– control what molecules
move into and out of them.

8. The Origin of Life
• Living cells also need genes.
• Scientists now believe that the first genes were
made of RNA, not DNA.
– Short strands of RNA can spontaneously
assemble from individual RNA nucleotides.
– RNA can replicate by itself.
• Liposomes may have captured RNA "genes,"
forming the first primitive cells on Earth.

9. Did Life on Earth Originate on Mars?
• In 1996, scientists found what resembled tiny,
fossilized bacteria in a Martian meteorite.
• Mars was once a much warmer and wetter planet.
• The supposed fossils may be too small to be
fossilized bacteria.
• NASA continues to explore the possibility of life on
Mars.

10. Early Life on Earth
• The origin of autotrophs
– Earth's earliest living organisms
• were marine prokaryotes.
• lived with no free oxygen.
• were heterotrophs that obtained energy and food from
outside sources.
– The evolution of autotrophs, organisms able to
convert inorganic molecules into food and organic
molecules, was a key event in the history of life.
• Photosynthesizers use energy from the Sun.
• Chemoautotrophs use energy from certain inorganic
chemicals.

11. Early Life on Earth
• The oxygenation of the atmosphere
– Cyanobacteria are photosynthetic bacteria that
produce oxygen as a by-product of
photosynthesis.

12. Early Life on Earth
• The first eukaryotes
– Eukaryotes appeared about 2 billion years ago.
– The nucleus and most organelles most likely
originated from inward foldings of the cell membrane.
– According to the endosymbiotic theory, mitochondria
and chloroplasts evolved from prokaryotes living
inside the earliest eukaryotic cells.

13. Charles Darwin and The Origin of Species
• For thousands of years, people believed that
species on Earth did not change.
• But then what are fossils?

14. Charles Darwin and The Origin of Species
• Jean Baptiste Lamarck argued that modern species
were descended from ancestors that had evolved to
become better adapted to their environments.
• Lamarck believed
that organisms
acquired new traits
over their lifetimes
and then passed
these traits to their
offspring. He called
this the inheritance
of acquired characteristics.

15. Charles Darwin and The Origin of Species
• Charles Darwin argued that evolution—inherited
changes in populations of organisms over time—
had produced all the living forms on Earth.

16. Charles Darwin and The Origin of Species
• Darwin was inspired by the observations he made as the
naturalist aboard the H.M.S. Beagle as it sailed around
South America from 1831 to 1836.
• For example, the 13 species of finches on the
Galápagos Islands varied in beak size and shape,
depending on their diet. How had the beaks of the
finches come to vary in this way?

17. Charles Darwin and The Origin of Species
• Darwin was also inspired by
– the work of geologist Charles Lyell, who argued
that Earth's geologic features were built by
gradual processes over millennia.
– the work of economist Thomas Malthus, who
wrote about famine and the struggle of humans
over resources.

18. How Natural Selection Works
• In any population of organisms, individuals have
many traits that show variation.
• Traits that are determined at least partly by genes
are heritable, passed from parents to offspring.
• Organisms that possess variable heritable traits that
are advantageous leave more offspring than
organisms without the advantageous traits. This is
natural selection.
• Advantageous traits become more common in a
population, resulting in adaptation.

19. How Natural Selection Works

20. Adaptation
• Adaptations are traits that make organisms well
suited to living and reproducing in their
environments.
• Adaptations can relate to various aspects of an
organism's life:
– Survival adaptations
– Sexual selection, which leads to the evolution of
adaptations that help organisms acquire mates
– Bearing and raising young

21. Staying Warm and Keeping Cool
• Mammals thermoregulate, maintaining
a fairly constant body temperature.
• The surface-area-to-volume ratio is an
important factor in thermoregulation.
It affects the size and shape of animals.
– Size: Animals found in cold habitats
are often larger than related species
living in warm habitats.
– Shape: Animals found in cold
habitats tend to have short legs and
small ears. Animals found in warm
habitats have long legs and large
ears.

22. Evolution and Genetics
• The incorporation of modern genetics into Darwin's
theory of evolution took place in the middle of the
20th century.
• This led to a focus on evolution as changes in the
allele frequencies of genes over time.
• Allele frequencies describe how common different
alleles for a gene are in the population.

23. Evolution and Genetics
• Mechanisms of Evolution
– Natural selection
• A specific allele may be advantageous and
allow organisms with the allele to reproduce
more than organisms with a different allele.
• More copies of the advantageous allele are
passed to the next generation, and the
frequency of the advantageous allele
increases in the population.

24. Evolution and Genetics
• Mechanisms of Evolution (continued)
– Mutation pressure
• A genetic mutation may be more likely to turn
one allele into a second allele than vice versa.
– Genetic drift
• Genetic drift is the evolution of populations due
to chance.
• Genetic drift is particularly important in small
populations.

25. Evolution and Genetics
• Mechanisms of Evolution (continued)
– Gene flow
• Changes in allele frequency result from the
movement of alleles into or out of a population,
such as through migration.

26. How Species Form
• A species is a group of organisms whose members
can breed with one another but not with members of
other species.
• Speciation is the formation of new species.
• The key to speciation is the evolution of
reproductive barriers that prevent two groups of
organisms from interbreeding.

27. How Species Form
• There are two kinds of reproductive barriers:
– Prezygotic reproductive barriers prevent
individuals of different species from mating or
prevent fertilization from occurring if they do
mate.
– Postzygotic reproductive barriers occur when
mating results in hybrids that do not survive or
are sterile, unable to reproduce.

28. How Species Form
• Two ways speciation can occur:
– In allopatric speciation, speciation occurs after a
geographic barrier divides a population into two
isolated populations.

29. How Species Form
• Two ways speciation can occur (continued):
– In sympatric speciation, speciation occurs without
a geographic barrier.
• Examples: hybridization and chromosomal
changes such as polyploidy

30. Evidence of Evolution
• Observations of natural selection in action
– Resistance to myxoma virus in Australian rabbits
– Peppered moth coloration and camouflage
– Antibiotic-resistant bacteria
– Evolution of the beaks of Darwin's finches after a
drought
– Many other documented examples

31. Evidence of Evolution
• Artificial selection
– In domesticated animals and crops, such as
dogs, racehorses, and corn
• Similarities in body structures

32. Evidence of Evolution
• Vestigial organs
• DNA and molecular evidence
– Similar DNA sequences in related species
• Patterns of development

33. Evidence of Evolution
• Hierarchical organization of living things
– Nested groups, or "groups within groups"
• Biogeography
– The study of how species are distributed on Earth
– Organisms evolved in a certain place and then
left descendants in the places where they were
able to spread.

34. Fossils: Earth's Tangible Evidence of
Evolution
• Fossils allow us to follow the evolution of certain
groups of organisms over time.
• The evolution of the whale blowhole

35. Fossils: Earth's Tangible Evidence of
Evolution
• The evolution and loss of whale hind legs

36. Fossils: Earth's Tangible Evidence of
Evolution
• Archaeopteryx, an early bird

37. The Evolution of Humans
• Humans are
– primates—we share an ancestry with monkeys
and apes.
– hominids—the primate group that includes Homo
sapiens and extinct relatives.

38. The Evolution of Humans
• The fossil record has allowed us to document some
aspects of human evolution.

39. History of Science: The Peppered Moth

40. History of Science: The Peppered Moth
• Peppered moths in England had always been light with a
scattering of peppery flakes. This made them well
camouflaged from birds (their main predators) in a
habitat of lichen-covered trees.
• During the Industrial Revolution, pollution caused trees
to become darkened with soot.
• More and more dark moths were seen in the peppered
moth population.
• After antipollution laws were passed, the soot
disappeared.
• Light moths increased in number. The dark moths have
all but disappeared.

41. History of Science: The Peppered Moth
• Kettlewell's experiments confirmed that natural selection
was responsible for changes in coloration in peppered
moth populations.
• Kettlewell released and recaptured marked moths. He
recaptured more dark moths in polluted habitats and
more light moths in unpolluted habitats.
• Kettlewell also placed moths on trees and filmed birds
eating the moths. Birds ate more light moths in polluted
habitats and more dark moths in unpolluted habitats.
• Challenges to Kettlewell's work resulted in his
experiments being repeated by Michael Majerus.
Kettlewell's results were confirmed.

42. Science and Society: Antibiotic-Resistant
Bacteria
• Antibiotic resistance has become a serious health issue.
• Antibiotic resistance is the result of natural selection.
• When a patient takes a course of antibiotics, a few
naturally resistant bacteria may survive the treatment.
These reproduce. Eventually, strains of bacteria exist
that cannot be controlled by the antibiotic.
• All antibiotic use contributes to antibiotic resistance.
• We must learn to take antibiotics only for bacterial
infections, and then to complete the course of treatment.
• Antibiotics should not be used to promote the growth of
livestock.

43. Science and Society: Antibiotic-Resistant
Bacteria
• Ways to slow the development of antibiotic
resistance in bacteria:
– Take antibiotics only when needed.
– Take the entire course of antibiotics.
– Use antibiotics responsibly in agriculture.