- Slides: 13
The Origin of Life Ch. 14, Sec. 2
Spontaneous Generation • Pre-17 th century it was believed that living things arose from nonliving things through a process called Spontaneous Generation
• 6 th century BC: Greek philosophers propose life arose when sunlight was shined onto mud • Why?
• 1600’s: It was believed that mice appeared from rotten grain • Why?
Francesco Redi (1626 -1697) • Mid-17 th century people believed flies were spontaneously generated from rotting meat • Redi was a scientist who noticed a life stage to the flies on the rotten meat – 1. Maggots – 2. Pupa – 3. Flies • He observed that the maggots appeared where flies had landed first
• Redi predicted that if the meat could be kept away from the flies, then there would be no maggots on the meat • He did not believe that flies spontaneously generated from meat!!! • So he set up his experiment…
• Control Group = uncovered jar of meat, flies layed eggs, which hatched into maggots, which turned into more flies • Experimental Group = covered jars of meat, flies have no chance to lay eggs, new flies do not appear
Louis Pasteur (1822 -1895) • Finally disproved spontaneous generation once and for all! 200 years after Redi’s experiment • Pasteur set up an experiment where boiled broth was exposed to air, but microorganisms couldn’t fall in
• By the 1800’s scientists understood (thanks to the microscope invented a century ago) that microorganisms (bacteria & viruses) caused people to get sick • But….
• Some scientists still believed that bacteria and viruses spontaneously generated from the air • Pasteur proved them wrong with his experiment
• Boiled broth was exposed to air in a specially shaped flask over a period of time but nothing grew • Once the neck was broken off bacteria grew in the broth • Bacteria did not spontaneously grow from the air!!!
• Thanks to Pasteur…. • Biogenesis = living organisms come from other living organisms