The Theory of Evolution

Biology

Mrs. Taktak / Mrs. Storey

Evolutionary TheoriesJean-Baptiste Lamarck (1744-1829)

• Theory that organisms change over generations

• Theory stated that acquired traits can be

inherited.

Example) Giraffes once had shorter necks, but with stretching for the leaves up high, successive generations had longer necks.

Question: If you had to have your arm amputated, would your children be at risk for missing an arm at birth? Why or why not?

Evolutionary Theories

Charles Darwin (1858)• Proposed the theory of Natural Selection.

• Studied in the Galapagos

Islands. (marine iguanas, finches)

• Wrote “Origin of Species”

Lamarck versus Darwin video

Modern Synthesis Theory

A more recent view of evolution that combines our understanding of heredity with genetics and evolutionary biology. The field of genetics gives scientists new insight into how natural selection and genetic drift work together.

Mechanisms Behind Evolution

• Natural Selection: favorable genetic variations that are better adapted to the environment survive and pass on those genes to offspring.

• Genetic Drift: the change in the gene pool of a population that takes place by chance. Often occurs through sexual reproduction.

• Genetic Mutations: Random changes in the DNA sequence, leading to a beneficial change for better adaptation in an environment.

The Theory of Natural Selection• I have called this principle, by which each slight variation,

if useful, is preserved, by the term Natural Selection.

- Charles Darwin, The Origin of Species

1. A slight mutation in the genes of an organism is favorable for certain conditions.

2. The organism survives and reproduces.

3. The favorable trait is passed on to offspring.

Natural Selection Video

Evidence supporting Evolution1. Fossil Record

– Comparing the fossils of ancient organisms to find relationships and possible common ancestry.

• Archeoptryx-a fossil

of an intermediate step

between a bird and reptile.

(only 6 have been found…)

Evidence for Evolution

• Radioactive Dating to support Fossil Record

– If you know the half-life of a given radioactive element, you can in principle use the decay of that radionuclide (ex. Carbon 14) as a clock to measure a time interval.

– Thus, we can measure the age of the Fossils

– Geologic Time Scale

– See changes over time

Adaptations

• An Adaptation = a characteristic to better help an organism survive.

-Structural: coloration, build

-Behavioral: nesting, parenting

Coloration• Camouflage- where animals coloring helps

it blend in with its surroundings.– Ex. Counter-shading

Question: How do you think this type of camouflage works?

Coloration• Mimicry: a harmless species imitates the

colors or appearance of a “harmful” one.

Viceroy Monarch

Coral Snake King Snake

Harmless bug..but you would probably stay away right?

Plant Adaptations

An example is the cactus…

– Modified leaves (needles)

– Ability to store water

– Needles for protection

Anatomical Similarities

• Homologous Structures

– Homo = same

– Similar structure which may show common ancestry.

– Example: the forelimbs of several different organisms have similar structure.

Examples of Homologous Structures

Physiological Examples

• Physiology of related organisms is very similar.

• Ex) The liver functions the same way in all mammals.

• Ex) The nervous tissue and function is similar in all animals.

Embryology

• •Embryology refers to the study of embryos.

•Scientists make comparisons of the embryos of several different species. Strikingly, it appears that nearly all life starts the same, tails, gill slits, etc.

•Cells differentiate the same as well.

Cat embryo

Human embryo

DNA sequences Scientists are mapping genes of different

organisms and observing many similarities between the DNA and RNA.

How closely are we related to yeast???

Vestigial Organs

• Body parts that were used in ancestors that are of no use today. – Ex. Wisdom teeth, appendix