EVOLUTION IN ACTION

Evolution takes millions of years However…there are some examples where evolution takes place rapidly

ANTIBIOTICS Some of the medicines developed in the 20th century are no longer effective in fighting bacterial disease. Bacteria have become resistant to antibiotics from decades of overuse

BACTERIA RESISTANCE Penicillin was discovered in 1928 by Alexander Flemming. It’s potential use in the treatement of bacterial diseases was not recognized until the 1940’s and then became a wonder drug at killing bacteria However, decades of use and exposing bacteria cells to penicillin has created resistant bacteria

When the bacterial population is exposed to an antibiotic, only the resistant bacteria survive. (blue: resistant bacteria; red: non-resistant bacteria…die from exposure with antibiotic The resistant bacteria live and produce more resistant bacteria. Today, penicillin no longer affects many species of bacteria because some species have evolved physiological adaptations to prevent them from being killed by penicillin.

What evolutionary process does this demonstrate? NATURAL SELECTION

There are other ways we are exposed to antibiotics Not just medicines & injections Use of antibacterial soap From beef & chicken we eat…farmers give antibiotics to cows & chickens to make them grow faster

Why doesn’t antibiotics work on flu/common cold? Antibiotics only kill BACTERIA Flu and common colds are caused by viruses

Natural Selection in Peppered Moths A change in the peppered moth populations was observed in England over a 50 year period. Before the mid-1800’s, most peppered moths were light gray. They blended in with the natural gray color of the tree trunks they sat on

But the industrial revolution hit England in the mid-1800’s Soot and pollutants settled on the trees outside the cities The bark became dark and the gray moths were easily seen by birds The gray moth population decreased, yet the dark moth population increased as they blended better