bio 112 exam 1

summer classes 2025, Basu

A scientific theory

broad, well supported, leads to predictions

stands against experimental tests

Based on natural phenomena and causes

5 misconceptions of evolution

1. Species always evolve into a “higher” or better beings

2. Evolution creates new forms of life by dramatic mutations

3. an organism can evolve during its lifetime

4. an organism can influence evolution of its own structure in response to its environment

5. Evolution is a random process

Reasons why those misconceptions are wrong

• Evolution is not goal-oriented.

• Evolution is survival of the fittest or adaptation

• Mutations change alleles and DNA

• Evolution does not happen in one generation (it takes a long time for it to happen)

• Changes happen within heritable characteristics

• Evolution is not a random process (neither is natural selection)

evolution

a change in the genetic composition of a popution from generation to generation

descent with modification

Earth’s many species are descendants of ancestral species that were different from the present-day species

Aristole

• Fixed ideal species (species do not change)

• Scala naturae (ladder of nature)

Linneaus

• Father of taxonomy

• Binomial naming

taxonomy

classifying organisms

Animals classifying in order (general to specific)

Domain, Kingdom, Phylum, Class, Order, Family, genus. species

(dumb king phillip came over for great soup)

Hutton

• gradualism

• geological change

Lyell

• Uniformitarianism

• rate of change today = rate of change in the past

• Earth is really old

• Principles of Geology

Erasmus Darwin

• Darwin’s grandfather

• Wrote ideas that “forms minute” slowly acquired over time

Lamarck

• linked evolution to adaptation

• extinct species have been replaced by descendants with new features

• Theory of inheritance of acquired characteristics (Lamarckism)

Adaptation

an inherited feature that helps an organism’s survival and reproduction

Charles Darwin

• Naturalist on HMS Beagle

• Collected plants, wildlife, and fossils

• Origin of Species (1859)

Wallace

• Had same ideas as Darwin in the malay archipelago (natural selection)

Natural selection

“survival of the fittest”; The reproduction of individuals with favorable genetic traits that survive environmental change because of those traits, leading to evolutionary change

• The mechanism for evolution

Two main ideas from Origin of Species

• Descent with modification

• Natural Selection

Phylogenetic tree

Diagrams used to reflect evolutionary relationships among organisms or group of organisms

• First sketched in 1837 by Darwin

Observation 1

Heritable variation exists in most species

Observation 2

All species produce more offspring than the environment can support

Inference 1

Unequal reproductive success among individuals

• Those with the “best traits” leave more offspring than others

Inference 2

Those heritable, favorable traits (adaptations) accumulate over vast time, matching species to their environment.

Theory of Evolution by Natural Selection

• Explains both diversity and unity of life

• Accounts for much of form and function

• Can predict outcome of environment change

• Genetic variation is ESSENTIAL for evolution by natural selection

Natural selection in action

• Antibiotic-resistance in bacteria

  • Surviving S. aureus gave rise to MRSA (methicillin-resistant Staphylococcus aureus)

  • methicillin: destroys an enzyme

Not Explained in Darwin’s Theory

• Origin of life

• How variation arises

• How inheritance works

• Why variation exists

• Sudden changes in fossil record

• Source of totally “new” characters

Evidence of evolution

• Fossil records

• Homology

• Convergence

• Biogeography

• Molecular Biology

Fossil records

• Many extinct species (ex. dinosaurs)

• Fossil Intermediates: seems to be an evolutionary transition between two groups of organisms (e.g., archaeopteryx, oldest known bird, and tiktaalik, characteristic of fish and land vertebrates).

Homology

• Forms related by common ancestry

• Homologous structures: structures derived from a common ancestor (but may be modified for different functions)

  • Similarities of mammal forelimbs are homologous

  • Result of divergent evolution

• Vestigial structures: remnants of ancestral (homologous) structures with no present adaptive function (ex, blind cave salamanders have eyes)

  • Infer: descended from a species that can see

  • Wisdom teeth, appendix, tailbone

Convergence

• Unrelated spp. Have similar adaptations (analogous structures) under similar environmental conditions

• Why? Convergent evolution (natural selection acted in the same way under same conditions)

  • Torpedo shape for swimming

  • White coats on arctic foxes and ptarmigan plumage

• Similarities occur not because of common ancestry but due to similar selection pressures

  • Tree-gliding mammals (flying squirrel and sugar glider)

• Independently, similar phenotyp

Biogeography

• Distribution of species

  • Corresponds to geographic history (isolated Australian marsupials)

• Wallace realized that deep ocean channel separating Asian islands from Australian islands explained great variation between similar habitats just a few miles apart

• Unique (endemic) species on islands are similar to nearest mainland species

  • Marine iguana (Galapagos Isl.) and tree-dwelling iguana (South America)

Molecular Biology

• DNA analysis supports evolution

• Closely related organisms have similar DNA

• Similar DNA sequences are the strongest evidence for evolution from a common ancestor.

  • Proteins in different mammals have amino acid sequence similarity

Species

• A group of organisms that can interbreed and produce viable, fertile offspring

  • Not based on similarity of appearance. Although appearance is helpful in identifying species, it does not define species

• A new species arises when the genetics in two populations becomes different enough that it prevents gene flow between the populations

Gene flow

• the movement of alleles across a species range

  • Movement of genetic material

Allele

One of a number of alternate forms of a DNA sequence at a particular genetic locus

biological species concept definition

Organisms that are reproductively isolated from each other are different species. 

Morphological species concept

Organisms that have significant morphological and anatomical differences are different species (E.g. sorting birds into species based on their wingspans and beak size)

Speciation

• Formation of two species from one original species

  • Evolution of modern elephants

• Speciation leads to biological diversity according to Darwin’s On the Origin of Species

Biological species concept

• Members of the same biological species:

  • Share the same gene pool

    • Gene pool: sum of all the alleles in a population

    • There is a gene flow between two populations

  • Are reproductively isolated from other spp.

    • By natural biological barriers

Problems with biological species concept

• Fossil species

• Asexual species

• Sometimes hybrids do happen naturally

biological reproductive barriers

prezygotic and postzygotic

prezygotic

does not let formation of the zygote happen

• Temporal