Darwinian Evolution

Aristotle’s ideas

• 384-322 BCE

• the scale of nature: it is like a ladder, on every rung there is a species

• there is no concept of evolution, whatever rung you were on is the one you stay on

Carolus Linnaeus’ ideas

Natural philosopher:

• classified and described organisms

• hierarchical classification system

• binomial nomenclature

Hutton

• theory of gradualism: rocks/world is changing before, now, and later (this is not static)

• what we see now is a result of gradual changes

Lyell

natural laws that operate now, have always been operating

• refined gradualism by uniformitarianism (a thought that the world is always changing)

• the laws that dictate how things change are now operating and will continue to operate

• they were both focused on how geological features changed over time

Jean baptiste lamarck

The first to apply theory to living organisms:

• species evolve through inheritance of acquired characteristics (theory)

An organism would change during its lifetime and pass down those changes to their offspring

• ex. giraffe (short neck- stretches neck to reach leaves → Modern-day giraffes have long necks

Darwins Ideas

Variation, overproduction, differential reproductive success, unequal ability to survive and reproduce, and how they use their resources

Variation

Members of a population often vary in their traits- variety

they are mainly individuals- very different

Overproduction

• Every generation, species has the capacity to produce more offspring than an environment can support

• More offspring are produced that can survive- differential survival and reproduction

Differential reproductive success

Those individuals with the most favorable combination of characteristics are more likely to survive and reproduce

Unequal ability to survive and reproduce

This leads to accumulation of favorable traits in the population over generations

• more favorable so they can reproduce more

How they use their resources

• Thomas Mattus provided that: natural resources are limited

• organisms must compete with each other for resources

• since there are more individuals than resources, some individuals do not survive

• there are other limits of population growth

Natural selection

is a mechanism of evolution

• individuals with more favorable heritable characteristics survive and reproduce at a higher rate than other individuals

“survival of the fittest”

• fitness: organisms’ ability to have offspring

  • better adapted organisms → more likely to survive and produce offspring

Population changes over time

it can change because of

• evolution

• the frequency of favorable traits increases over generations

• and because of less favorable traits (more scarce)

When the environment changes

natural selection may result in adaptation to these new conditions

• it may give a rise to new species

natural selection does not create new traits

it edits the traits in the population gen

Evidence for natural selection

artificial selection, direct observation, homology, and fossil record

Artificial selection

is selective breeding done by humans

• it is meant to pass on desirable traits to the next generation

• specific traits are selected and become more common in a population → this increases the fitness of individuals with that trait (selective breeding)

• ex. agriculture

Direct observation

is a response to introduced species

• they move into new locations editing already existing alleles

• ex. antibiotic resistance

• soapberry bugs

  • when fruit changed, bugs evolved to have shorter beaks

Homology

is the similarity resulting in common ancestry

• they are homologous structures

  • they look similar but have different functions

• ex. limbs

  • humans

  • whales

  • sharks

  • birds

Fossil record

it remains in sedimentary rocks

• fossils in rock layers show us where or when ancient organisms existed

  • it infers lines of descent

• sedimentary layers

  • each layer represents a different era