Ch. 22 Descent with Modification, A Darwin View of Life

Darwin’s view on evolution and what helped lay out his groundwork

• great diversity of organisms: The Origin of Species 1859

• current species are descendants of ancestral species

• def. of evolution: descent with modification, can be viewed as both a pattern and a process

• fossils helped lay the groundwork, found in sedimentary rock

Scala Naturae and Classification of Species

• Aristotle viewed species as fixed and arranged them on a scala naturae

Carolus Linnaeus

• father of taxonomy, branch of biology concerned with classifying organisms

• interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose

• developed the binomial format for naming species

Georges Cuvier, James Hutton & Charles Lyell, and Jean-Baptiste de Lamarck

Curvier: developed the study of fossils (paleontology), speculated that the boundaries between strata represent catastrophic events

Hutton & Lyell: thought changes in Earth’s surface resulted from slow, steady actions still operating today at the same rate, influenced Darwin’s thinking

Lamarck: species evolve through use and disuse of body parts and the inheritance of acquired characteristics, unsupported by evidence

Lamarck vs. Darwin

Lamarck: theory held that species underwent changes in response to changes in their environment

Darwin: theory was one of natural selection and survival of the fittest

Darwin and the Voyage of the Beagle

• collected specimens of South America

• observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions

• perceived adaptation to the environment and the origin of new species as closely related processes (finches)

Ideas from The Origin of Species

• the unity of life (descent with modification summarizes this- all organisms are related through descent from an ancestor that lived in the remote past)

• diversity of life

• the ways organisms are suited to life in their environments

reasoned that large morphological gaps between related groups could be explained by this branching process and past extinction events

Artificial Selection, Natural Selection, and Adaptation

• humans have modified other species by selecting and breeding individuals with desired traits (artificial selection)

Darwin drew two inferences and two observations: members of a population often vary in their inherited traits, all species can produce more offspring than the environment can support, many of these offspring fail to survive and reproduce (will lead to accumulation of favorable traits in the pop. over generations)

Who largely influenced Darwin?

Thomas Malthus

Does natural selection increase the frequency of adaptations that are favorable in a given environment?

Yes, can only increase or decrease heritable traits that vary in a population

What are the 4 types of data that document evolution?

• direct observations

• homology

• the fossil record

• biogeography

Evolution by natural selection can occur rapidly in species with what generation times?

short, and evolution relies on mutations or changes in DNA sequences.

Homology

similarity resutling from a common ancestor

• homologous structures are resemblances that represent variations on a structural theme present in a common ancestor.

What is comparative embryology?

it reveals anatomical homologies (similarities) not visible in adult organisms

• ex. all vertebral embryos have a post-anal tail

Vestigial structures

• remnants of features that served a function in the organism’s past

• genes shared among organisms inherited from a common ancestor

• so just things we don’t use anymore (tail bone, wisdom teeth, etc.)

What are evolutionary trees?

diagrams that reflect hypotheses about the relationships among different groups, homologies form nested patterns in evolutionary trees

• can be made using different types of data, like anatomical and DNA sequence data

Convergent evolution

is the evolution of similar, or analogous, features in distantly related groups (so look similar, not a common ancestor)

• arise when groups independently adapt to similar environments in similar ways, but doesn't provide info. about ancestry

The Fossil Record

provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

• fossils can document important transitions

Homologous Structures

similar anatomy/structure, different uses

Analogous structures

different anatomy/structure, but similar uses

Biogeography

the scientific study of the geographic distribution of species, provides evidence of evolution

• after pangaea moved, this allows us to predict when and where different groups evolved

Endemic species

species that are not found anywhere else in the world

• islands have many endemic species that are often closely related to species on the nearest mainland or island