ENVIRONMENTAL SCIENCE

Chapter 4 The Organization of Life

4.2 Evolution

4.2 Evolution Objectives• Explain the process of evolution by

natural selection.• Explain the concept of adaptation.• Describe the steps by which a

population of insects becomes resistant to pesticide.

Introduction• Organisms tend to be good at what

they do and designed for where they live.– For example, the chameleon can change

colors, use its tongue to shoot out and grab insects, and hold onto branches with specialized feet

– The chameleon’s eyes also turn on turrets on its head so that it can watch insects with a minimum of movement

Evolution by Natural Selection

• In 1859, English naturalist Charles Darwin published On the Origin of the Species by Means of Natural Selection which proposed natural selection as the mechanism by which evolution occurs.

• Evolution, the concept that species change over time, had been around long before the work of Darwin, however, this explanation fit all existing evidence and has survived repeated experiments.

Evolution by Natural Selection

• Darwin noted that species differ slightly from one another in form, function, and behavior.

• He also noted that some of the differences were hereditary – passed on from one generation to the next.

• Darwin had no knowledge, however, of the work of the Austrian monk Gregor Mendel that would become the foundation for modern genetics.

• Darwin also realized the role of environmental pressures exerted on each individual of a species.

Evolution by Natural Selection

• Darwin proposed that some individuals, because of certain traits, are more likely to survive and reproduce.

• Natural selection is the term that Darwin used to describe the unequal survival and reproduction that results from the presence or absence of particular traits.

• A trait is any characteristic that an individual possesses.

• An adaptation is any trait that gives a survival advantage to an individual.

Evolution by Natural Selection

• Darwin viewed nature as selecting for certain traits and organisms with those traits tended to survive and reproduce.– For example, lighter bones in birds allowing them

to fly, brighter feathers in some male birds to attract a mate

• Over time, the population would include more and more individuals with the advantageous traits.

• As the population changes, so does the species.

Evolution by Natural Selection

• Coevolution is the process in which two species evolve in response to long-term interaction with one another.– For example, flowers

produce nectar to attract insects which pick up pollen on one plant and transfer it to another plant while feeding

Evolution by Artificial Selection

• Many species of plants and animals have been selectively bred through the ages for desired characteristics.

• The selective breading of organisms by humans for specific characteristics is called artificial selections.

• Seed from the largest, sweetest fruit and the most nutritious grains were repeatedly saved to plant again for progressively more productive crops throughout the last 10,000 years.

• Docile animals that produce much meat for comparatively little effort were repeatedly bred for domestication.

Summary of Natural Selection

• There is variation within any species.• Species tend to produce far more offspring

than are necessary for survival of that species.

• There is a limited amount of resources available.

• The combination of overproduction and limited resources leads to fierce competition over the available resources.

Summary of Natural Selection

• Competition for resources results in “survival of the fittest”.– “Survival of the fittest” is the most misunderstood

phrase in science– “Survival of the fittest” means that the individuals who

are the best adapted have a better chance to survive and pass their genes on to the next generation

– Those who have adaptations that give them an advantage over others in the population still are not guaranteed survival and reproduction

Summary of Natural Selection

• After many generations under selective reproductive pressures favoring some traits and not favoring others, the gene pool shifts to a point that it is distinctly different from the original gene pool – hence a new species.

• Evolution, the fact that species have changed over time, is not in debate in the scientific community.

• The rate at which evolution occurs is, however, open to a degree of interpretation.

The Peacock Story

Evolution of Resistance• Human actions have actually resulted in

resistant pests and pathogenic bacteria.• Resistance is the ability of one or more

organisms to tolerate a particular chemical designed to kill it.

• Some individuals in the population may have certain genes that allow them to break the chemical down into a harmless substance.

Evolution of Resistance• Through our use of pesticides, we have been

promoting the evolution of more resistant pests.• Over prescription and improper use of antibiotics

has led to many resistant forms of pathogenic bacteria.– For example, a pesticide may be sprayed onto corn to

kill grasshoppers– The bulk of the grasshoppers die, but a few survive– The survivors have some advantage over the others,

and are able to pass that trait on to the next generation

– Each time the grasshopper population passes on its genes to the next generation

– After many sprayings, the entire population may become resistant to the pesticide.

References• Chameleon Feeding - http://

imagedir.empas.com/imginfo.html?f=V&c=3367&e=7

• Chameleon on Branch - http://www.pete-online.us/Images2/Kerry

• Bromeliad - http://www.sjsd.k12.mo.us/Schools/mbio/photos/1999Images/plant_life/pages/bromeliad.htm

• Fennec Fox - http://www.catbox.com/florian/photos/photo_ani.html

References• The Origin of Species -

http://www.catbox.com/florian/photos/photo_ani.html • Charles Darwin (younger image) - http://

www.froes.dds.nl/ • Charles Darwin (older image) -

http://4umi.com/image/people • Insect Pollination - http://

faculty.uca.edu/~johnc/representative_plant_groups.htm

References• Peacock -

http://www.fcps.k12.va.us/KingsGlenES/stuact/stupages/endanim/peacock.htm

• Resistant Bacterium Illustration - http://www.bioteach.ubc.ca/Biodiversity/AttackOfTheSuperbugs

• Methicillin Resistant Staphylococcus aureus - http://idinchildren.com/200403/frameset.asp?article=ca-mrsa.asp