A HISTORY OF LIFE

1
A HISTORY OF LIFE
2
Origin and Evolution of the Universe

• Entire universe arose about 15 billion years ago.
• The solar system started taking shape about 5
  billion years ago.
• The sun ignites as condensed hydrogen gas atoms
  begin fusing to form helium.
• The earth starts to coalesce and cool about 4.5
  billion years ago.
• The early earth was rich in water, silica,
  metals, heavier molecules, and other rocky
  components. 
• Early oceans became salty as carbonates, Mg2,
  K, and other ions accumulated as acids (e.g.,
  H2CO3, HNO3, H2SO4) interacted with water and
  inorganic matter.  
• Atmosphere arose as the earth formed and as
  out-gassing occurred from within the earth, CO
  (carbon monoxide), CO2, H2S (hydrogen sulfide),
  CH4 (methane), and NH3 (ammonia).  The
  characteristics of the early atmosphere is based,
  in part, on what planetary astronomers have
  discovered from other planets in the solar
  system.
• Conditions on earth, before life began - Refer to
  Figures 18-6 and 18-7 on pages 380 and 382 in the
  textbook
• First protobiont appears about 3.5 billion years
  ago. 

3
Origins of Primeval Life

• In the 1930s, Alexander I. Oparin from Russia and
  J. B. S. Haldane from England, proposed that life
  arose under certain conditions that allowed for
  abiotic formation of organic compounds. 
• Oparin and Haldane assumed that three conditions
  had to exist
• Anoxic atmosphere  (presence of free oxygen would
  tend to interfere with chemical reactions that
  transform simple organic molecules into complex
  ones)
• Precursor molecule supply had to be in abundance
• A source of  Energy existed to start and keep the
  process going (electrical, chemical, light, etc.)

4
Stanley Millers Experiment

• In 1953, Stanley Miller (in Urey's Lab) tried to
  replicate such conditions in the laboratory to
  see what would happen. 
• In a sterile vessel containing no O2, Miller
  mixed a molecule supply (i.e., H2, CH4, H2O, and
  NH3), a source of energy (i.e., an electric spark
  - other folks have used UV light), and modulated
  the temperature from 0-100 C over the course of
  one week. 
• At the end of the week, Miller collected samples
  of the "primordial soup" and analyzed it. 
• Constituents of the soup did not contain life,
  but it did contain complex organic
  macromolecules, including amino acids,
  nucleosides, polyphosphates, and others.
• Refer to Figures 18-8 and 18-9 on pages 384 in
  the textbook.

5
(No Transcript)
6

• The Protobiont the first living cell
•  
• How it formed, no one really knows. 
• Some properties associated with living cells can
  arise from the interactions between organic
  macromolecules, water, and the environment. 
• Most probably, the transition from a non-living
  complex system of macromolecules to a living
  organism somehow occurred by a yet undetermined
  means in accordance to the natural laws of
  chemistry and physics. 
• Due to the relative complexity of a living cell,
  even a single-celled prokaryote, some scientists
  have ventured the hypothesis that life could not
  arise through abiotic (non-living) processes in
  the time scale (about 1 billion years) that it is
  thought to have occurred. 
• The panspermia hypothesis suggests that life came
  to earth from some external source. 
• The late Francis Crick, in his 1981 book, Life
  Itself, proposed that life was brought to earth
  by intelligent extraterrestrials. 
• The recent suggestion that meteorites from Mars
  might contain fossilized remains of ancient
  organisms has continued to fuel the debate (refer
  to Figure 18-10 on pages 385 in the textbook). 

7
What happened after life began?

• Early life forms were probably unicellular and
  resemble modern day prokaryotes.  After life got
  started, it probably existed in an anaerobic
  environment.  As more complex biochemical
  pathways evolved, such as photosynthesis, waste
  products produced of such processes (i.e.,
  oxygen) were toxic to existing organisms.
• Geological Evidence
• uranite - UO2 precipitates in stream beds.  Early
  atmosphere was probably lt 1 O2 .  Geologic
  record indicates uranite started to accumulate
  about 2 billion years ago.
• iron oxide or rust suddenly starts to accumulate
  in rock that are 2-3 billion years old
• Biochemical Evidence
• Early attempts of cellular respiration, early
  stages of this process do not require oxygen
  (glycolysis, fermentation), but later stages
  require oxygen (oxidative respiration).

8
The origin of eukaryotes and the origin of
membrane-bound organelles

• Lynn Margulis (1967) has been a strong advocate
  for the Endosymbiont hypothesis.
• This hypothesis proposes that mitochondria and
  chloroplasts became incorporated into cytoplasm
  of eukaryotes through the symbiosis of larger
  cells with with bacteria (mitochondria and
  flagella) and cyanobacteria (chloroplasts) -
  refer to Figure 18-16 on page 392 in the
  textbook.
• Prokaryotes, mitochondria, and chloroplasts
  possess similar genomes each type contain a
  naked circular loop of DNA.
• ribosomes produced by prokaryotes, mitochondria,
  and chloroplasts are similar in size and
  structure and smaller than those found in the
  cytoplasm of eukaryotic cells
• inner membranes of mitochondria and chloroplasts
  are similar to the plasma membranes of bacteria.
• mitochondria, chloroplasts, and prokaryotes
  reproduce asexually through binary fission.
• antibiotics that inhibit protein synthesis in
  bacteria also do the same to mitochondria and
  chloroplasts but not to inhibit protein synthesis
  mediated by the nucleus

9
Early Eukaryotes

• About 2.5 billion years ago, a billion years
  after the origin of the first protobionts,
  eukaryotes evolved and proliferate. 
• We would recognize many of these forms as being
  similar to modern day amoebae, protozoa, and
  unicellular green algae. 
• Multicellular life forms do not appear in the
  fossil record until about 0.6 bya during a period
  of vast change on the face of life.

10
Cambrian explosion - "Life's Big Bang" occurred
about 600 million years ago

• Evidence of this preserved as fossils in the
  Burgess Shale in British Columbia, Canada.
• Animal Phyla in the Burgess Shale include 
  Porifera, Brachiopoda, Arthropoda, Echinodermata,
  Hemichordata, and Chordata (each phylum
  represents a different body plan).
• Other phyla present in fossil record are extinct.

11
Major evolutionary trends

• Over the past 600 million years there has been an
  explosion of animal, plant, and fungal diversity.
  
• A transition from being unicellular, filamentous,
  or forming small colonies of cells toward
  becoming multicellular.
• greater complexity
• development of organs and organ systems
• changes in reproductive strategies
• development of adaptations to exist in and
  exploit a terrestrial environment
• greater interdependence/more interactions among
  different species

12
IF THE HISTORY OF LIFE WERE PLACED ON A 24 HOUR
SCALE (Keep in mind that these times are
approximate)

• Midnight - first protobiont or life forms come
  into existence (approx. 3.5 billion years ago) or
  midnight.  Prokaryotes rule!  Evolution of
  photosynthesis eventually leads to accumulation
  of  toxic levels of oxygen -  leads to mass
  extinction.
• 1017 a.m. - first eukaryotes (e.g., unicellular
  organisms - protozoan-like).
• 818 p.m. - trilobites and other aquatic
  multicellular organisms appear in earth's oceans
  (Cambrian explosion).
• 834 p.m. - first vertebrates (e.g., marine and
  fresh-water fish).
• 915 p.m. - land plants first appear.
• 936 p.m. - winged insects take to the land and
  air.
• 1034 p.m.- mass extinction.
• 1118 p.m. - dinosaurs rule.
• 1119 p.m. mass extinction (approximately 75 of
  all life goes extinct).
• 1133 p.m. (approximately 65 mya) - adaptive
  radiation of birds and mammals.
• 1159 p.m. - Humans arrive on the scene (200,000
  years ago).
• 115956 p.m.- Birth of human civilization.

13
HUMAN EVOLUTION

• Mammals- share characteristics with other mammals
  such as  vertebrate with a spinal chord,
  skeleton, skull housing a large brain, ability to
  give birth to live offspring, mammary glands,
  hair or fur, and common ancestry.
• Humans differ from other mammals
• Teeth
• canines - for tearing and piercing (most
  carnivores)
• incisors - nip and cut food (rodents)
• premolars with cusps - grinding and crushing
  (horses)
• molars with cusps - grinding and crushing
  (cattle)
• Early and more primitive mammals have 66 teeth
  modern mammals have 44 humans have 32.
• The incidence of Wisdom teeth appear to be
  diminishing (natural selection?) in human
  populations (in Central Europe, one or more
  wisdom teeth are missing in 19 of population. 
  Wisdom teeth or third molars are common among
  Native Americans, but not among Africans).
• Offspring have an extended period of learning.
• Humans have an overall larger brain size.
• Humans possess behavioral flexibility

14
TRENDS IN PRIMATE EVOLUTION

• Change in overall skeletal structure and mode of
  locomotion - bipedalism (able to move on 2
  appendages for extended periods of time with
  minimum energy loss) -refer to Figure 17-21 and
  1725 on page 368 and 371 in the textbook .
• Modification of hands - humans can cup hands and
  possess a opposable thumb - refer to Figure 17-23
  on page 370 in the textbook
• Less reliance on sense of smell and more reliance
  on sense of daytime and color vision, and depth
  perception.
• Change in dentition - primates moved from eating
  insects to more fruits and vegetables to becoming
  omnivorous - adaptation of teeth is probably
  caused by natural selection, so that the kinds of
  teeth best able to accommodate a particular diet
  become enhanced over time - refer to Figure 17-23
  on page 369 in the textbook.
• Brain expansion - more elaborate.
• Gorilla 600 cm3
• Humans 1350 cm3
• Higher intelligence may have resulted from tool
  making, need for better memory, or to increase
  ability to anticipate jumps (from branch to
  branch) or throws (weapons and spears). 
• Behavioral and cultural evolution- ability to
  learn and mimic behavior.  ex. language.

15
CULTURAL EVOLUTION

• Biogeographic Origin of Humans ?Africa.
• The movement to different types of environments
  may have influenced cultural evolution. 
• Cultural evolution tends to be Lamarckian because
  changes can be acquired and passed on. 
• Examples are language, tool making, technology,
  and domestication of plants and animals. 
• The transition from humans making a living as
  hunter/gathers to an agriculturally-based
  civilization started about 12-14,000 years ago,
  based on archeological evidence.

16
ANCESTORS OF MODERN HOMO SAPIENS

• Mitochondrial "Eve" determined through lineage
  coalescence all human descending from a very
  small population _at_ 150,000 to 200,000 years ago. 
  
• These dates are inferred based on the fact that
  mitochondrial DNA is maternally inherited and on
  assumption that mutations in this DNA happen at
  consistent rate. 
• Thus far the fossil evidence from South Eastern
  Africa tends to support these findings.

17
The family tree for primates

• Prosimians - lemuroids lemurs, lorises, etc.
• Tarsioids - tarsioids tarsiers
• Anthropoids - ceboids new world monkeys
• Cercopithecoids - old world monkeys prehensile
  tails
• Hylobatids - gibbons, siamang
• Pongids - orangutan, gorilla, chimps
• Hominids - humans and their most recent ancestors

18
Humans and Chimpanzees

• Morphologically humans and apes are distinct from
  one another. 
• Based on molecular data, isozyme polymorphisms
  and sequences of mitochondrial and genomic DNA,
  humans and apes, in particular, chimpanzees are
  quite similar. 
• The A, B, and O blood type system for humans and
  chimpanzees are the same.
• Humans and chimpanzees share 52 of the same
  gene alleles. 
• Nucleic acid differences are even less, 1.1
  percent difference. 
• Should humans be classified as Pan sapiens
  instead of Homo sapiens, or should chimpanzees be
  called Homo troglodytes instead of Pan
  troglodytes? 
• Was the common ancestor to humans and chimpanzees
  separated by the Great Rift Valley in Africa,
  leading to allopatric speciation? 
• Humans probably evolved in response to changing
  environmental conditions as forests gave way to
  savannas.  Some evidence supports this
  hypothesis, but it is far from conclusive.

19
Did Humans Arise from Apes?
20
Are human descended from apes?

• The answer is NO! Based on scientific data, it
  appears that humans and apes share a common
  ancestor whose lineage diverged 15-20 million
  years ago.
• Apes and humans probably share a common ancestor.
• The common ancestor may have been ape-like, but
  it was not an actual ape in the modern sense.