EVOLUTIONARY

THEORY

What is biological evolution?

• Successive genetic changes in a population over many generations.

• New species result as genetic characteristics are modified due to:– Mutation: change to DNA (random, predictable) – Isolation: events that separate populations– New allele combinations: results in variety w/in

populations– Environment: constant or changing – Reproduction: sexual/asexual, rates

• Implies natural processes are at work

• Humans have been manipulating the genetics of populations since we first domesticated animals and plants

• Rather than allowing natural events to determine the combination of genes, we select for specific traits to combine

SELECTIVE BREEDING results in ARTIFICIAL SELECTION

• Artificial selection results in new varieties of dogs, cats, horses, tomatoes, corn, etc.

Evolutionary theory suggests the same

genetic mechanisms are at work in nature…

but through Natural Selection

History of Evolutionary Thought

Jean–Baptiste Lamarck (1744-1829)

Theory of Use and Disuse

• Environmental change causes changes in the needs of organisms

• Changing needs cause changing behavior

• Changed behavior leads to changes in the use of a structure

• Body parts used more often become stronger and larger, while unused parts slowly waste away and disappear

Theory of Inheritance of Acquired Characteristics

• Modifications that occur during an organism’s lifetime can be passed on to its offspring.

Lamarck’s theory of use/disuse in the giraffe

INCORRECT!

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Lamarck

Think about it... • Can you make yourself any height you want?• If you lose an arm, will all your kids have one

less arm?• If you are born with a birthmark, will all your

kids have it to?

Thomas Malthus (1766-1834)• Political economist • Essay on the Principle of Population

(1798)• Darwin was influenced by his writings• Observed that animals and plants

produced far more offspring than can survive

• Hypothesized that populations will grow to a size that can be supported by the environment

• Overpopulation leads to hunger, disease, & struggle for survival.

• Related these concepts to human populations, poverty, and famine

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Alfred Russel Wallace (1823-1913)

• British naturalist• 19th century's leading expert on the

geographical distribution of animal species

• Best known for independently proposing a theory of evolution due to natural selection that prompted Charles Darwin to publish his own theory

Wallace• noted that natural barriers like water, mountains, canyons, etc.

resulted in greater diversity in populations• observed that similar environments result in similar adaptations

even though populations have different geographical origins

OSTRICH EMU RHEA AFRICA AUSTRALIA SOUTH AMERICA

Wallace theorized the birds have similar structures because their environments are similar

Charles Darwin (1809-1882)• So who is Darwin?• English naturalist• Stationed on the HMS Beagle for 5

years (traveled around the world, mostly the southern hemisphere, including the Galápagos Islands) from 1831 to 1836

• Published On the Origin of Species in 1859 introducing his theory of “natural selection” based on his observations while aboard the Beagle

Voyage of the HMS Beagle

Darwin’s Finches

• Good example of how biological evolution occurs

• Each Galapagos Island has its own unique species of finch

• Each finch has a head and body well-adapted for life on that island

• The finches are different species, but look similar

• Darwin realized that the finches had a common ancestor

• He proposed that originally a few seed-eating finches had flown to the islands from the mainland. Over millions of years, the finches adapted to the foods available on each island – and evolved into separate species.

In conclusion……

• NATURE had selected which finches were best fit for that type of environment.

• Finch Game

1. There is variation within populations: Individuals of the same species have natural genetic differences

• Genetic• raw• material for• change

Darwin’s Theory of Natural Selection

2. Living organisms over produce: They reproduce more than will survive (incorporated from Malthus)

Darwin’s Theory of Natural Selection

Darwin’s Theory of Natural Selection3. It’s a struggle to survive: Individuals must compete

for food, space, water, mates, etc.

4. Environment determines which traits are successful: Favorable traits are passed on to offspring and become adaptations

Darwin’s Theory of Natural Selection

Natural Selection in a Nutshell

Darwin’s Main Ideas from On the Origin of Species

1. DESCENT WITH MODIFICATION• Newer species appear to be descended from older

species• Species may be descended from one or a few

original species

2. NATURAL SELECTION• Characteristics of the environment “select” traits that

increase a population’s ability to survive• Those organisms with favorable traits (adaptations)

are best suited and are more likely to survive to reproduce and pass their traits on to offspring, giving those offspring an adaptive advantage

• Those that do not possess favorable traits are more likely to die, and thus, they do not reproduce, removing those traits from the gene pool

• Over time, a species’ variation increases from the original population, thus, the species has diverged genetically or evolved

Darwin’s Main Ideas from On the Origin of Species

“Survival of the Fittest”

• Those organisms best-adapted for their current environment (the fittest) will survive to pass on the genes for those favorable adaptations to their offspring

• Has nothing to do with strength, size, or health

Video Summary