Why is all life on earth-related?
It all evolved from a common ancestor
Overall, what was the general sentiment of early thinking of species diversity?
Described life as being created, not evolved
According to the Pre-Darwin way of thinking, what was the reasoning behind fossil organisms not resembling living ones?
-extinction of species must occur
What are some different reasons given for extinction?
- natural disasters (Cuvier)
- apparent disappearance of species was actually one species changing slowly into another (Lamarck)
- supernatural disasters
- not actually extinct, just hiding
What explanation did Cuvier give for the succession of life-forms in earth’s strata?
- a catastrophe occurs, which results in local extinction and the presence of fossils in the stratum
- after the catastrophe, a new species will move into the area, followed by another catastrophe and another layer of fossils
What did Cuvier believe about evolution?
- did not believe in evolution, thought that species do not change over time (fixed)
- believed in the interdependence of organs to survive, if some organs changed, the organism would not survive
What did Lamarck believe about evolution?
- species change over time (evolution) because the characteristics an individual acquires during their lifetime can be passed on to their offspring (thought traits can be passed on in a single generation)
- the use and disuse of structures results in heritable change eg: giraffes need long necks so they gained them (had an innate drive to improve)
What were the drawbacks of Lamarck’s ideas?
-there was no experimental evidence of his ideas and his logic was greatly flawed
Did Lamarck believe in extinction?
Said extinction was rare and that species just changed
What were James Hutton’s main ideas?
- uniformitarianism (our present is the key to the past)
- gradualism (the features of the earth result from a slow accumulation of events- catastrophes are rare)
What significant contributions did Charles Lyell make concerning evolution?
- advocated uniformitarianism and gradualism
- made Hutton’s ideas accessible to a wide audience-including Darwin
Did Darwin write about the survival of the fittest?
-the survival of the fittest was not discussed by Darwin, this statement is inaccurate because it only focuses on how the fit will survive and overlooks the aspect of reproductive success (it does not address roots of evolution)
What did Darwin observe on his voyage that was critical in his future theories?
- similarity and dissimilarity in the same species of finches
- redundant forms from one place to another (common ancestry) but also variation within a region
What were Darwin’s 5 observations?
- organisms produce many more offspring than survive to reproduce themselves
- most populations are relatively stable
- resources are limited (not enough for all offspring of individuals) - there is variation among individuals within a species (no understanding of genetics)
- some variation is heritable
Explain Darwin’s three inferences
- organisms must compete for limited resources and not all succeed (struggle for existence)
- some heritable variations provide individuals with a competitive advantage (allows them to survive in the conditions of their environment and achieve survival/reproductive success)
- individuals with advantageous variations are likely to leave more offspring than individuals without these variations
Explain the concept of relative fitness
- Individuals have many traits/variations, some are better for survival, while some are better for reproduction
- traits that have a high frequency of survival and reproduction are the ones that are passed on
Explain the process of “descent with modification”
- explains how species change and diversify over time
- the idea that a lack of resources results in competition, and some individuals have heritable variations that provide a competitive advantage, making them more likely to leave more offspring than those without variations
- as a result, have more individuals with that variation than were present in previous generations
- the overall result is adaptive changes over generations
Explain some important characteristics of Natural Selection
- gives rise to adaptations
- as individuals adapt to different environments, new species may arise over time (over many generations)
- populations evolve, not individuals (can’t pass traits in a single generation)
- natural selection acts on existing variation
- is context-dependent (species change in the context of what will help them survive in their environment)
Explain the statement “natural selection has no innate tendency towards perfection”
A species cannot be perfectly suited to its environment because then it can’t adapt and survive when the environment changes, therefore there is no tendency to perfectly suit the environment
Why can’t acquired traits be inherited?
Because acquired traits involve changes in the phenotype, not in the actual DNA (genotype)
Phenotypic Variation
-involves variation in form, function, and behavior
Genotypic Variation
-involved variation in the genetic makeup itself
What are the conditions for natural selection to act on variation?
- must be expressed in the phenotype (seen by environment)
- must be heritable (caused by genotype)
Is Natural Selection random?
- no, natural selection is always directed towards one extreme state/variant
- however, variations in species are random
