1.C.3 Populations Evolve

Populations of organisms continue to evolve.

Scientific evidence supports the idea that evolution has occurred in all species.

Scientific evidence supports the idea that evolution continues to occur.

As predicted in Rachel Carson’s book Silent Spring, we now are

confronted with the unintentional artificial selection

of organisms resistant to pesticides. Chemical-tolerant

individuals are surviving to reproduce until resistant

individuals are beginning to outnumber the ones susceptible

to our methods of control.

Pesticide Resistance

Pesticide-Resistant Organisms:

• Super Rats that can consume up to five times the lethal amount of rat poison

• Head lice resistant to treatment • DDT no longer effective against disease

vectors such as mosquitoes • Fruit flies resistant to malathion • The Colorado potato beetle has evolved

resistance to 52 different compounds belonging to all major insecticide classes (multiple resistance)

Pesticide Resistance

http://www.pbs.org/wgbh/evolution/library/10/1/image_pop/l_101_02.html

Grants’ observations of

Darwin’s finches in the Galapagos

Peter and Rosemary Grant have been studying the beaks of Galapagos

finches since 1973.

drought

drought

Directional selection occurred after a drought in 1977.

The finch beaks became larger as they adapted to thickly-shelled nuts. Large beaks are

energetically expensive, though, and the allele frequencies soon began to reverse.

Evolution of limbs in

tetrapods

Some evidence that evolution continues to occur:

• Increase in antibiotic-resistant bacteria such as MRSA and Clostridium difficile

• Evolution of the SARS virus and other emergent diseases

• Lactose tolerance in Europeans

• Butterflies in the South Pacific have evolved resistance to a killer bacteria in a single year