3 Main Questions:
- What is speciation?
An evolutionary process in which one species splits into two or more species.
- What is macroevolution?
Evolutionary change above the species level, including the origin of a new group of organisms or a shift in the broad pattern of evolutionary change over a long period of time.
- What is biological species concept?
Definition of a species as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring, but do not produce viable, fertile offspring with members of other such groups.
5 Main Facts:
- A species may originate from an accident during cell division that results in extra sets of chromosomes, a condition called polyploidy.
- A second form of polyploidy can occur when two different species interbreed and produce hybrid offspring.
- Many hybrid zones are stable in the sense that hybrids continue to be produced.
- The fossil record includes many episodes in which new species appear suddenly in a geologic stratum, persist essentially unchanged through several strata, and then dissappear.
- The punctuated pattern suggests that once the process begins, speciation can be completed relatively repidly a suggestion confirmed by a growing number of studies.
Diagram:
A mutation in one gene cayses the shell of the Japanese land snail (a) to spiral in the opposite
direction from others. Snails with opposite spirals cannot mate, resulting in reproductive isolation.
Summary:
The "mystery of mysteries" that captivated Darwin is speciation, the process by which one species
Speciation fascinated Darwin and many other biologists because it is responsible for the tremendous
diversity of life, repeatedly yielding new species that differ from existing ones.
Speciation also forms a conceptual bridge between mocroevolution, changes over time in allele
frequencies in a population, and macroevolution, the broad pattern of evolution over the long time
spans.
Video:
No comments:
Post a Comment