Evolution

Science Before Darwin

• Before Darwin, most people believed that species existed exactly as they were created by a divine creation.

• Scientists began to seek explanations for the origins of fossils.

• This began the idea that living things changed over time.

Jean Baptiste Lamarch

• Proposed hypothesis for how organisms changed over generations.

• He believed: over the lifetime of an individual, physical features increase or decrease in size because of its use or disuse. These features were then passed on to offspring.

• What he did get right: environmental conditions affect species.

Lamarck’s Theory

Charles Darwin

• Naturalist – Sailed around the world on the HMS Beagle

• Found evidence that species evolve, or changed over time, and that was the basis for life’s diversity.

• Conducted his study of plants and animals on the Galapagos Islands off of South America.

Darwin

• Developed the most accepted theory of evolution.– Father of Evolution

• He explained the process of evolution through natural selection.

Evolution by Natural Selection

• Most organisms can produce more offspring than can survive.

• Organisms differ from place to place because of their habitats.

• Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits.

Evolution by Natural Selection

• This “survival of the fittest” is the driving force behind the change in a species.– Natural Selection

• In time, the number of individuals with favorable characteristics will increase in a population.

• Therefore, the nature of the population changes-evolution.

Evolution by Natural Selection

• Each species that has evolved has accumulated adaptations in response to their environment.– Adaptations are some feature that has a

selective advantage

Plant Adaptations• Desert plants have modified structures to

allow them to survive better in their hot, dry climate

• Examples:– Stomata (pores) that only open at night when

it is cooler– Thorns for protection– Waxy covering to reduce water loss– Fine, hair like fuzz to protect against wind and

sun– Small leaves they drop in severe drought

Mimicry vs. Camouflage

• Mimicry– The resemblance of one organism to another

or to an object in its surroundings for concealment and protection from predators

• Camouflage– Concealment by disguise or protective

coloring so as to make the wearer indistinguishable from the surrounding environment

Monarch Butterfly

Viceroy Butterfly

Coral Snake

Colubrid Snake

Species Formation• Environments differ from place to place

– Temperature, food available, amount of space

• Populations of the same species living in different locations tend to evolve in different directions.

• As two isolated populations of the same species become more different over time, they may eventually become unable to breed with one another.– Reproductive Isolation– The two populations then become 2 separate

species

Species Formation

The ecological niches exert the selection pressures that push the populations in various directions.

Species Formation• Sometimes unrelated species become more

similar as they adapt to the same kind of environment

– convergent evolution

• They've evolved similar adaptations because they occupy similar niches -- dining on ants, hunting in the high grass, or swimming in the dark

• Ex: the different sorts of anteaters, found in Australia, Africa, and America. Though not closely related, they all evolved the "tools" necessary to subsist on an ant diet: a long, sticky tongue, few teeth, a rugged stomach, and large salivary glands

Darwin’s Theory

• Variations exists within the genes of every population or species.– Ex: eye color, fur color, size, beak shape

Darwin’s Theory

• In a particular environment, some individuals of a population or species are better suited to survive (result of variation) and have more offspring (natural selection)

Darwin’s Theory

• Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population.

Darwin’s Theory

• There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct.

Tempo of Evolution

• Gradual changes over LONG periods of time– Gradualism– Most accepted

• The thought that successful species may stay unchanged for long periods of time then evolution occurs in spurts because of major environmental changes in the past– Punctuated Equilibrium

Evidence of Evolution

• Homologous Structures– Similar physical structures that share common

ancestry

Homologous Structures

Homologous Structures

Evidence of Evolution• Analogous Structures

– Structures that are similar but evolved SEPERATELY, NOT from a common ancestor

– Occur because of convergent evolution

Vestigial Structures

• Vestigial Structure– A structure in an organism that is reduced in

size and function that may have complete and functional in an ancestor

Vestigial Structures

Evidence of Evolution

• Fossil Records!

Archaeopteryx (left) and a pigeon (right).

Evidence of Evolution

• Biological Molecules– Proteins

• Amino acids linked together make proteins• Species that have fewer differences in between the

sequence of amino acids share a common ancestor

– Nucleic Acids• Nucleic acids linked together form DNA• Species that have fewer differences in the

sequence of nucleic acids share a common ancestor

Evidence of Evolution

• Embryonic Development

Example of Evolution

• Antibiotic Resistant Bacteria– Mutations (changes) in the nucleotide

sequence (DNA) of the bacteria change the way the bacteria grows, eats, and behaves allowing it to grow in the presence of antibiotics

MRSA (Methicillin-Resistant Staphylococcus Aureus)

Development of a New Species

• Over time, variations that arise within a population as a result of natural selection can have 2 major outcomes:– Speciation

• The accumulation of differences between groups (divergence) forms a new species

– Extinction• A species that could no longer survive in their

current environmental conditions and dies out completely

Populations can Evolve through:

• Genetic Drift– Random change in allele frequency in a

population due to a chance event– Ex: a fire or landslide could reduce the

population to only a few individuals; if just one of the individuals is lost it can have major effects in the frequency of an allele

– Cheetahs have been seriously affected by this due to their drastic population decline and most cheetahs alive today are direct descendants of only a few individuals

Populations can Evolve through:

• Nonrandom Mating– Individuals prefer to mate with others that live

nearby or are of their own phenotype– Inbreeding (mating with relatives) is an

example that causes a lower frequency of heterozygotes but increases frequency of homozygotes

• Self-fertilizing plants fall in this category

– Also occurs when organisms choose their mate based on certain traits (size, color, ability to gather food, etc)

Populations can Evolve through:

• Gene Flow– Movement of genes into or out of a population

due to interbreeding – Individuals will move into or out of a

population (migration) and will add alleles to the population or remove them

– Ex: when wind carries seeds far beyond the bounds of the parent plant population the genes are removed from the original population and then added to the new population

Populations can Evolve through:

• Genetic Mutation– Any change in the sequence of a DNA strand

due to chance or environmental causes

• Natural Selection– Organisms better adapted to their

environment and have favorable variations will be more likely to survive, reproduce, and pass on those traits thus increasing the frequency of those traits in a population