The History of Life

Spontaneous Generation  The belief that life arose from non-living things.  As scientific thinking progressed through the ages, free-thinkers set out to prove that spontaneous generation was not true. Play video

Examples 1. Redi performed a test that showed meat didn’t become flies, but rather flies laid their eggs in meat and maggots in the meat became flies. 2. Louis Pasteur showed that life did not come from “gravy.” Broth is boiled. Broth remains free of microorganisms. Curved neck is removed. Microorganisms grow in broth

The fossil record  The fossil record provides evidence about the history of life on earth.  It also shows how different organisms, including species, have changed over time.

Earth’s early history  4.6 billion years old  Earth’s early atmosphere probably contained hydrogen cyanide, CO 2, CO, N, H, S, and H 2 O.  There was no free oxygen; free oxygen was the result of organisms doing photosynthesis and releasing oxygen as a by-product into the atmosphere.

Free oxygen  The ancient atmosphere had no free oxygen.  Prokaryotes (later eukaryotes) began photosynthesis as a means to obtain energy.  The by-product (oxygen) accumulated in the atmosphere => ozone  The rise of oxygen in the atmosphere drove some life forms to extinction, while other life forms evolved new, more efficient metabolic pathways that used oxygen for respiration.

The first organic molecules: Miller and Urey pg. 424  Miller and Urey’s experiments suggested how mixtures of the organic compounds necessary for life could have risen from simpler compounds present on a primitive earth.  They filled a flask with H, CH 4, Ammonia, and H 2 O, made certain no microorganisms could get in, and passed electric sparks through the mixture.  Over a few days, amino acids (building blocks of protein) formed. 1. Play video 2. Play video

The puzzle of life’s origins  Formation of microspheres: under certain conditions, large, organic molecules can form tiny bubbles called proteinoid microspheres.  They are not cells, but they do have: 1. selectively permeable membranes 2. a simple means of releasing and storing energy 3. over time, they grow and divide.

Evolution of RNA and DNA  Under the right conditions, RNA can help DNA replicate.  Some RNA can grow and duplicate itself.  Some RNA can catalyze chemical reactions.  Scientists believe RNA came before DNA.

Origin of eukaryotic cells the endosymbiotic theory (Lynn Margulis, Boston University)  Eukaryotic cells formed from a symbiosis among several different prokaryotic organisms.  Early prokaryotes (primitive mitochondria and chloroplasts) that could process energy began living together, formed communities, then eventually complex eukaryotic organisms.

Sexual Reproduction and Multicellularity  Some time after eukaryotes arose, they began to reproduce sexually.  Prior to that, organisms reproduced through simple division.  Sexual reproduction shuffled genes, and added diversity, making more variations.  A few hundred million years after the onset of sexual reproduction, organisms became multi-cellular.

Read pgs about the timeline of the earth.

Patterns of Evolution  Macroevolution: large-scale evolutionary patterns and processes that occur over long periods of time.  6 important topics in macroevolution: 1. extinction 2. adaptive radiation 3. convergent evolution 4. co-evolution 5. punctuated equilibrium 6. changes in developmental genes

Extinction  More than 99% of all species that have ever lived are now extinct.  Reasons include: competition/loss of resources, etc.  Mass extinctions wipe out entire ecosystems, collapsing food webs and disrupting energy flow in the ecosystem.  Whatever the cause (volcanoes, asteroids, etc.), the result is that the disappearance of certain organisms will open up habitats and niches that allow organisms to flourish and new species to appear. Play video

Adaptive Radiation  A single species or a small group of species has evolved, through natural selection, into diverse forms that live in different ways (like Darwin’s finches or dinosaurs).  The loss of the dinosaurs opened up the opportunity for mammals to grow new species and spread out.

Convergent Evolution  The process by which unrelated organisms come to resemble one another.  How does this happen?  Sometimes groups of organisms undergo adaptive radiation in different places or at different times but in ecologically different environments.  Organisms may start out with different raw material (DNA) to work with, but as time progresses and they face similar environmental demands, they come to resemble each other over time.

Co-evolution  Organisms that are closely connected to one another by ecological interactions evolve together.  Example: some flowers have very specific flower, shape, and odor that attract very specific pollinators.  If the flower’s pollinator changes, a change in the flower may change as well.  An evolutionary change in one organism may be followed by a corresponding change in another organism.  Co-evolution: when two species evolve in response to changes in other over time.

Punctuated Equilibrium  Long, stable periods (millions of years) interrupted by brief periods (hundreds of thousands of years) of more rapid change. ex: horseshoe crab has remain unchanged when compared to its ancient fossils; no selection pressures = no change. They are still in equilibrium.  Controversial amongst scientists who study evolution.  Evolution has proceeded at different rates for different organisms at different times during the long history of the earth.

Developmental Genes and Body Genes  The timing of cell differentiation and gene expression can have an impact on organisms and the generations that come from them.