History of Life and Evolution

How Life Began (Blue Book, Ch.12, p. 252)

Conditions on Earth were very different from today – no oxygen in the atmosphere, but did contain carbon dioxide, water vapor, methane and ammonia gases.

Formation of the basic (organic) chemicals of life from non-living (inorganic) molecules.

Several different hypotheses:

  1. Primordial soup model (scientists Oparin, Miller, Urey) – inorganic molecules chemically reacted with each other to form organic molecules, including amino acids, with the input of energy from solar radiation, volcanic eruptions and lightening.
  2. The Bubble Model (Lerman)

Gases from undersea volcanic eruptions were trapped in bubbles where, protected from damaging ultraviolet radiation, chemical reactions took place that formed simple organic molecules. When bubbles rose to the surface and burst, these chemicals were released into the atmosphere. The energy from lightening and ultraviolet radiation caused more chemical reactions that formed more complex organic chemicals which fell into the ocean, starting another cycle.

  1. Meteorite hypothesis

Organic molecules have been found on meteorites and asteroids and may have arrived on Earth with impacts.

How the first cells formed

  1. Iron –sulfide bubble hypothesis (Martin and Russell) explains how cell membranes may have formed
  2. Lipid membrane hypothesis (Morowitz) proposes that lipid molecules spontaneously formed a bi-layer lipid membrane that could protect organic molecules such as amino acids fatty acids, sugars and nucleotides from the environment.

Formation of the first genetic material

Cech and Altman proposed that RNA, not DNA, first stored genetic information. RNA can copy itself and make more RNA, without the enzymes that DNA needs for these functions.

Other scientists who contributed to origin of life hypotheses

  • Louis Pasteur – refuted the concept of spontaneous generation (organisms arising out of nothing). Showed that sterile broth will not grow bacteria, only contaminated broth.
  • Lynn Margulis – found evidence that supports the endosymbiotic theory (Mitochondria are the descendants of symbiotic, aerobic eubacteria and Chloroplasts are the descendants of symbiotic, photosynthetic eubacteria)
  • Sydney Fox – suggested that first amino acids were formed due to high temperatures near undersea volcanic vents (has since been refuted)

How long ago (years) / What happened
4.5 bill / Earth formed; was a ball of molten rock
4 bill / Earth began to cool; oceans formed
3.5 bill / First bacteria
3.8 bill / Primitive prokaryotic cells
3 bill / Photosynthetic bacteria produce oxygen
1,8 bill / Eukaryotic cells appear
800 mill / First multicellular organisms appear
Around 700 mill / “Snowball Earth”
600 mill / Formation of ozone layer; “explosion” of life
420 mill / Plants on land
370 mill / Amphibians
360 mill / Insects
340 mill / Reptiles
230 mill / Dinosaurs and Mammals
195 mill / Birds
65 million – present / The Age of Mammals
7-5 million / First hominids (walking upright, hand-graspers)
3-2 million / First homo species (Homo habilis, homo erectus)
190,000-160,000 / First humans like us
40,000 / First humans like us outside of Africa

Vocabulary terms (Blue Book Ch.12, sec.1)

Term / Definition
Radiometric dating / Estimating the age of an object by measuring its content of certain radioactive isotypes. Radioisotopes decay (break up) and give off energy over a known period of time.
Fossil / Remnant of living organism
Creation of life / Most scientists believe that the basic chemicals of life (organic chemicals) developed from inorganic chemicals (the newly formed earth contained chemicals in its crust and its gas atmosphere). No one knows yet exactly how that happened
Prokaryotes / Single cell organisms without organelles or a nucleus
Eukaryotes / Cells of these organisms have a nucleus and organelles; include fungi, plants and animals
First living organisms / Prokaryotes (eubacteria and archaebacteria see p.1038)
Cyanobacteria / The first bacteria on earth; were photosynthetic; over hundreds of million years they put oxygen into atmosphere
Fossil / Preserved or mineralized remains (bone, tooth, shell) or imprint of an organism that lived long ago
Most likely found in rock/sediment layers. In amber, tar, frozen or mummified is not as common
Protists / The first eukaryotic organisms; today’s algae

Evolution - Ch.13, Section 1

  • Who was Charles Darwin and around what time did he live?
  • A British naturalist; around the middle of the 19h century
  • What did most people in Darwin’s time believe about the creation of species?
  • That god put all species into the world and they exist unchanging
  • Why was Darwin afraid to share his ideas?
  • His ideas were contrary to those of theChristian church and the common beliefs of his time.
  • What was Lamarck’s theory?
  • Individuals change physical characteristics while alive (example: giraffe gets longer neck because it keeps stretching upward to eat)
  • Individuals pass on these new characteristics to offspring
  • Which part of Lamarck’s theory is wrong?
  • That individuals adapt and change during their lifetime
  • Who gave Darwin the idea for natural selection?
  • English economist, Robert Malthus
  • What are the four major points of Darwin’s theory of evolution?
  • There is variation in the genetic material between individuals because of random genetic changes (mutations)
  • Individuals with better adaptations are more likely to survive and produce offspring (=natural selection)
  • Over time, traits that make individuals of a population better able to survive and reproduce, tend to spread in that population.
  • There is overwhelming evidence for the idea that species evolved from organisms that are now extinct

Evolution / Change over time
The same vs. different species / Individuals may seem similar but cannot interbreed with each other unless they have the same number and kind of chromosomes and live in the same area
Humans and apes cannot interbreed; donkeys and horses can (also zebras and horses, lions an tigers)
Population / All the individuals of a species that live in a specific geographic area, and that can interbreed
Descent with modification / Parents pass traits on to offspring but there are small changes over time
Natural selection / Individuals that are better adapted to their environment are better able to survive and produce offspring
Adaptation / Inherited trait that has become common in a population because it provides a selective advantage
Reproductive isolation / Two populations of the same species do not interbreed because of geographic separation or another barrier to reproduction
Gradualism / Gradual change over a long period of time leads to species formation
Punctuated equilibrium / A model of evolution in which periods of rapid change in species are separated by periods with little or no change
Paleontologist / Scientist who studies fossils
Vestigial structures / Structures, usually bones, are considered to be evidence of an organism’s evolutionary past
“Tail bone” in humans; pelvis in whales
Homologous structures / Structures that share a common ancestry
See p. 286
All vertebrates have the same kinds of bones in their forelimbs even though they now function and look differently
Divergence / Accumulation of differences between groups
Speciation / Process by which new species form
If I built a city right through the middle of a forest, the frogs on either side would not be able to mate with each other any longer. Over time they would become more and more different.
Subspecies / When populations that belong to the same species start to differ genetically because they have to adapt to a different environment, they become subspecies
Coevolution / Back and forth evolutionary adjustments between interacting members of a community.
Example: If zebras run faster, lions have to run faster also
Convergent evolution / Similarities evolve in some organisms not related to each other because they live in similar environments. The similar structures are called analogous.
Example: wings in bats vs wings in butterflies
Adaptive radiation / The diversification, or evolution, of many different species from one ancestral species
How do we know that whales evolved from a land animal? / Vestigial evidence: whales have some remnants of bones no longer needed
Embryological evidence: embryos of whales and land animals are very similar
Molecular evidence: similar milk protein genes as in certain land animals

Evidence for evolution (Ch.13, sec.2)

  1. Fossil evidence: shows orderly patterns of evolution

Example: p.284, fig.8

  1. Anatomy and development: bone structures are most similar in organisms that have the most recent common ancestor

Examples:vestigial structures (p.286)

homologous structures

embryos of all animals look very similar

  1. Biological molecules – as species evolve, there should be more and more changes (mutations) in the species’ DNA

Example: amino acid sequences for hemoglobin (a protein in the blood that carries oxygen) are most similar for species that have the most recent common ancestor (p. 287, fig.10)

Darwin’s finches (p.290):

Darwin collected individuals of 9 different finch species in the Galapagos Islands, all very similar except for their beaks. Darwin suggested that they all had a common ancestor and developed different beaks in order to adapt to different food sources (divergence). If species become different enough they may form a new species (speciation). First they are considered a subspecies but if they continue to change they become different enough to form a new species that cannot interbreed with the original species.

Evidence that evolution is occurring right now:

  • Bacteria become more resistant to antibiotics over time (blue book, pg. 289)
  • The flu virus mutates (evolves) over the course of just a few months and the flu vaccine must be reformulated every year
  • You can get a cold more than once because the virus mutates all the time

Evolution explains unity (similarities between all living things) and diversity (differences between living things)

Factors in Natural Selection:

  • Only individuals who survive can reproduce
  • More offspring are born than the environment can support
  • Individuals that are better able to cope with their environment are more likely to leave offspring

Hominid evolution(Green Book p.379)

Hominoids include:

  • Lesser apes: Gibbons
  • Great apes: orangutans, chimpanzees, gorillas
  • Hominids: includes all the species in the human lineage, both modern and extinct.

Human Family History (includes only the most recent and most well-known)

  • Homo habilis- left Africa
  • Homo erectus: invented the use of fire and emigrated all over the world; maybe had language
  • Homo neandertalensis: sophisticated humans; buried their dead; may have had language; became extinct 40,000 years ago, maybe because of us (homo sapiens); stockier and stronger than us
  • Homo sapiens: modern humans

Features of hominids:

a. walking upright (bipedal);

  1. longer lower limbs than upper limbs,
  2. opposable thumbs,
  3. large brains
  • Bipedalism predated large brains and tool use; the ability to use hands for foraging, carrying things and infants, and using tools may have stimulated brain development.
  • Jaw development: jaws became smaller as hominids became more intelligent; the reasons for that are not clear
  • Brain size: relative size is related to intelligence (as evidenced by more and more sophisticated tools). Tool use started about 2.5 mill years ago; largest increase in brain size happened between 800,000 and 200,000 years ago, maybe because frequent climate change made life more challenging
  • Once tool use became essential in acquiring food, hands may have evolved to become more sophisticated

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