pages 444-453 Flashcards
theory of evolution by natural selection
formulated independently by Charles Darwin and Alfred Russel Wallace; explains how organisms have come to be adapted to environments.
special creation
leading explanation for the diversity of organisms prior to Darwin. Beliefs were explained by the instantaneous and independent creation of living organisms by a supernatural being.
3 assumptions of special creation
1) All species are independent, in the sense of being unrelated to each other
2) Life on Earth is young – perhaps just 6000 years old
3) Species are immutable, or incapable of change
Scientific theories usually have two components:
a pattern and a process.
pattern component
a statement that summarizes a series of observations about the natural world. About facts – about how things are in nature.
process component
mechanism that produces that pattern or set of observations.
plato
claimed that every organism was an example of a perfect essence, or type, created by God, and that these types were unchanging. Acknowledged that the individual organisms present on Earth might deviate slightly from the perfect type. Key to understanding life was to ignore the shadows and focus on understanding each type of unchanging, perfect essence.
typological thinking
based on the idea that species are unchanging types and variations within species are unimportant or even misleading.
aristotle
organized organisms into a linear scheme called the great chain of being, or the scale of nature. Proposed that species were organized into a sequence based on increased size and complexity, with humans at the top. Characteristics of species were fixed.
assumptions made by aristotle
1) Species are fixed types
2) Some species are higher – in the sense of being more complex or “better” – than others
evolution
proposed by Lamarck; species are not static but change through time.
Lamarckian evolution
claimed that simple organisms originate at the base of the chain by spontaneous generation and then evolve by moving up the chain over time. Progressive in the sense of always producing larger and more complex species. Also contended that species change via the inheritance of acquired characteristics – an individual develops in response to its environment and its phenotype changes and passes these to offspring (long necks on giraffes).
Darwin and Wallace
emphasized that evolution occurs because individuals with certain traits leave more offspring than others.
population
consists of individuals of the same species that are living in the same area at the same time.
population thinking
claim by Darwin; instead of being unimportant or an illusion, variation among individuals in a population was the key to understanding the nature of the species.
Theory of evolution was revolutionary:
1) Overturned the idea that species are static and unchanging
2) Replaced typological thinking with population thinking
3) It was scientific. Proposed a mechanism that could account for change through time and made predictions that could be tested through observation and experimentation.
descent with modification
Darwin; species that lived in the past are the ancestors of the species existing today, and that species change through time.
The pattern component of the theory of evolution by natural selection makes two predictions about the nature of species:
1) Species change through time
2) Species are related by common ancestry
fossil
any trace of an organism that lived in the past.
fossil record
consists of all the fossils that have been found on Earth and described in scientific literature. Fossil record suggests over 99% of all the species that have ever lived are now extinct.
extant species
those living today
sedimentary rocks
form from sand or mud or other materials deposited at locations such as beaches or river mouths. Relative ages.
geologic time scale
a sequence of named intervals called eons, eras, and periods that represented the major events in Earth history. Indicates that the Earth is much older than 6000 years as proposed by proponents of special creation.
radioactive decay
steady rate at which unstable or parent atoms are converted into more stable daughter atoms. Can assign absolute ages.
radiometric dating
reveals that Earth is about 4.6 billion years old and the earliest signs of life appear in rocks formed 3.4-3.8 billion years ago. Based on:
1) Observed decay rates of parent to daughter atoms
2) The ratio of parent to daughter atoms present in newly formed rocks
3) The ratio of parent to daughter atoms present in a particular rock sample
Cuvier
published a detailed analysis of an extinct species called the Irish “elk.”
law of succession
extinct species in the fossil record were succeeded by similar species.
transitional feature
trait in a fossil species that is intermediate between those of ancestral and derived species.
vestigial trait
a reduced or incompletely developed structure that has no function, or reduced function, but is clearly similar to functioning organs or structures in closely related species.
phylogenetic tree
a branching diagram that describes the ancestor-descendant relationships among species or other taxa.
homology
similarity that exists in species because they inherited the trait from a common ancestor. All three interact.
genetic homology
occurs in DNA nucleotide sequences, RNA nucleotide sequences, or amino acid sequences.
developmental homology
recognized in embryos.
structural homology
similarity in adult morphology, or form.
Chemicals that cause cancer in humans
can often be identified by testing their effects on mutation rates in bacteria, yeast, mice, etc. because the molecular machinery responsible for copying and repairing DNA is homologous in all organisms.
Drugs intended for human use can be tested on mice or rabbits
if the molecules targeted by the drugs are homologous.
Unknown sequences in human, rice, or other genomes
can be identified if they are homologous to known sequences in yeast, fruit flies, or other well studied model organisms.
Speciation
process that results in one species splitting into two or more descendant species.
Internal consistency
most powerful evidence for any scientific theory; observation that data from independent sources agree in supporting predictions made by a theory.
