Spontaneous generation vs. biogenesis How does life begin? Spontaneous generation vs. biogenesis

SPONTANEOUS GENERATION In the early 1600’s, some scientists believed that life began spontaneously!

Recipe for Bees Kill a bull during the first thaw of winter. Build a shed. Place the dead bull on branches and herbs inside the shed. Wait for summer. The decaying body of the bull will produce bees.

SPONTANEOUS GENERATION Process by which life begins when “magical ethers” enter non-living things to make them alive Examples: mice were thought to come from garbage piles, geese from the mud banks of the river, maggots from meat In the 1600’s, scientists began challenging this idea.

Francesco Redi

Redi’s Experiment Set-up 3 jars with rotting meat Open top Sealed with lid Covered with cloth Observations Maggots No maggots

Lazzaro Spallanzani

Spallanzani’s Experiment Set-up Nutrient broth heated Flask left open Flask sealed Observations Bacteria grew No bacteria grew

Louis Pasteur

Pasteur’s Experiment Set-up Nutrient broth heated Flask with curved neck Flask with straight neck Observations No dust could reach broth, no bacteria grew Dust settled, bacteria grew

EVIDENCE AGAINST SPONTANEOUS GENERATION The experiments of Redi, Spallanzani, and Pasteur showed the life does not arise spontaneously LIFE must come from LIFE These experiments supported the theory of biogenesis

BIO= life GENESIS= the beginning BIOGENESIS BIO= life GENESIS= the beginning

BIOGENESIS Living things come from other living things. They do not arise spontaneously!

REFERENCES Biology: The Web of Life. Scott Foresman-Addision Wesley http://vilenski.org/science/notebook/unit1/historyoflife/spallanzani.html