Theories of Evolution

• Evolution – slow, gradual change over time.• Geologic evolution – changes in the non-living planet

over time.• Biological evolution – changes in living organisms over

time.

Jean Baptiste LaMarck 1809

• Early Theory of Evolution

– (gradual changes in species over time)

• Use and Disuse – He hypothesized that organisms were able to develop new structures as they needed them and they were able to pass them on to their offspring. This was called the..

• Theory of Inheritance of Acquired Traits

• Got evolution right, but got mechanism wrong !!

• Inherited Traits – characteristics genetically passed on the offspring.

• Acquired Characteristics – a trait that develops during an individual’s lifetime.

Charles Darwin• 1809-1882

• Ships naturalist aboard the HMS Beagle collected hundreds of specimens and made extremely detailed observations of the natural world on the 5 year scientific expedition. Upon his return and further study of geology and natural population increase, he developed his Theory of Natural Selection

• Wrote (1845) his famous book“On the Origin of Species”

Darwin’s Theory of Natural Selection

• #1 Overproduction• Organisms tend to have many more than two

offspring so at least some will survive (yet populations usually do not grow rapidly in the wild)

#2 Competition - Therefore they

must compete for resources

(food, space, mates)

Natural Selection

• #3 Variation - variation within the population.

• #4 Adaptation - Therefore some of them must be better adapted to their environment

• #5. Natural Selection- the ability of organisms that are best adapted to survive and reproduce . Those that are less well adapted will not survive.

Speciation• Eventually, over generations and time,

new species will evolve from older forms by natural selection of better adapted forms.

Fitness

• Which is more fit???

Evidence for EvolutionAll of the fields of Life Science show evidence of evolution.

• A. The Fossil Record– Fossil: the remains or evidence of past life recorded in rock.– (molds, impressions, bones, shells, teeth, preserved in ice, etc.)– 1. Fossils are found most often sedimentary rock.– 2. Relative age can be determined by the fossils position in the

layers. The oldest fossils are found below the younger ones.– 3. Absolute dating uses the principal of radioactive dating

• The half-life of known radioactive compounds never changes.• (ex. Carbon 14 found in bones and shells can determine their actual

age in years).• Ex. Fossil remains clearly show the gradual evolution of the modern

horse.

Fossil Record

B. Comparison of Similar Anatomy or Structures

1. Homologous structures - those that appear to have come from a common ancestor. These indicate that species are related.

• Ex. Bats wing, human arm and whale flipper bones.

2. Analogous structures - those that are used for the same function but are not similar. These indicate species are not related.

3. Vestigial structures – those that no longer serve a useful function

• Ex. Human appendix, tailbone (coccyx)

Bones of the Mammalian Forelimb

Comparative Anatomy

Comparative Embryology

• Comparative Embryology – examination of differences and similarities in embryo development (before birth).

• ex. Comparison of bird, fish and early human embryos

E. Behavior Comparisons

• Biochemical Comparisons • Recent developments (Human Genome Project) have

allowed for the comparison of DNA from different species and groups within species. This new evidence is the strongest yet that consistently supports accepted evolutionary theory.

– DNA - our DNA and that of a Chimpanzee is more than 99% identical. Gorillas and Baboons have somewhat less (95-97%) and mice have 80% identical DNA.

– Protein and Enzymes – Ex. Cytochrome C, a respiratory enzyme common to all

animals is slightly different in different species. Humans differ from monkeys by one amino acid in their cyt C. We differ from pigs by 10 amino acids. Chicken cyt C has 13 different amino acids and fish differ by 21. This clearly shows the accepted evolutionary relationship between vertebrates.

F.

Molecular Comparisons

Sources of Variation• A. Mutation• A mutation is a change in the DNA of an

organism due to external or internal factors. (toxins, radiation, random,etc.)

• Most mutations are NOT beneficial to the organism.

• Some may become beneficial if the environment changes, provided they do not harm the individual. (ex. Giraffe’s neck)

Genetic Recombination

• Sexual reproduction leads to new combinations of genes.

• Ex. You are not exactly like either one of your parents.

• C. Speciation• New species will arise more quickly if they are

geographically isolated. Natural barriers such as mountains, deserts, rivers or landslides can separate members of a population. If they can no longer interbreed they may change enough by natural selection to become a separate species.

• (ex. Darwin’s finches)• The loss of the ability to interbreed is called

reproductive isolation. Sometimes this is caused by changes in reproductive organs such that the offspring will not survive.

• Sometimes this type of isolation is caused by changes in courtship behavior or the timing of mating cycles.

Speciation

• Geographic isolationGeographic isolation of populations• Can lead to

• Reproductive isolation of population • Can lead to

• New Species

• (unable to breed when together)

Geographic Isolation

• Members of a population may become isolated from one another by geographic boundaries like mountains, rivers or even oceans

Reproductive Isolation

New Species Evolve

V. Evolutionary Time Frames

A. Gradualism: species descend from a common ancestor gradually as the change in minor ways over a long period of time.

B. Punctuated Equilibrium a newer theory developed by Stephen Jay Gould states that species remain fairly constant over long periods of time until a great change in their environment cause relatively rapid speciation.

Gradualism

• Seen often in the fossil record of marine invertebrates like snails.

Punctuated Equilibrium

• Seen in the evolution of birds from dinosaurs

Gradualism

Convergent Evolution

Divergent Evolution(Adaptive Radiation)

• Evolution is a fact – species do change over time!!

• Natural Selection is a scientifically supported theory that explains this fact.

• Decades of experimental and observational evidence support Darwin’s theory of

Evolution by Natural Selection