Evolution Flashcards
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Q1: Natural selection – inspiration from Malthus
English clergyman Thomas Malthus argued, in “An essay on the principle of population,” that policies to help the poor were doomed because population growth would always outstrip food production.
Natural selection
Darwin (and Wallace) realized that all organisms must experience the same thing. Individual members must compete, directly or indirectly, consciously or unconsciously, for the limited resources needed to survive and reproduce. Any trait that better enables them to do this will cause those bearers to leave more offspring than others lacking the trait. Because offspring are more likely to have the trait, the trait will become proportionately more common in future generations.
Critical ingredients for natural selection
Observation 1: There is excess fertility such that more offspring are produced than the environment can support. Inference 1: There must be a fierce struggle for existence among members such that only a (sometimes very small) portion of offspring survive to reproduce.
Observation 2: Individuals vary (i.e., no two are exactly the same). Inference 2: Success in the struggle for existence is not random but depends, in part, on traits facilitating it. This is the process of natural selection.
Observation 3: Much of this variation is heritable. Inference 3: Across generations, traits that increase success will become more common. This is evolution by natural selection.
Natural selection
Is a process that occurs when certain conditions are met; i.e., it is deductive reasoning. If these conditions are met, then this outcome must occur in a given situation:
Individuals vary in a trait.
There is a non-random association between the trait and an individual’s reproductive success (i.e., their ability to survive and reproduce relative to other individuals in the population; also known as their ‘Darwinian fitness’).
The trait is heritable.
Then: The trait will evolve (i.e., its frequency or value will change across generations). 1 & 2 are necessary for natural selection to occur; 1, 2 & 3 are necessary for natural selection to produce evolutionary change.
Darwin’s evidence for natural selection
1) Deductive reasoning – if these conditions exist (and observation indicates they clearly are), it’s the necessary outcome.
2) It is consistent with the observation that organisms are so well suited to survive and reproduce in their environments (i.e., it explains adaptation).
3) An analogy with artificial selection – Darwin noted that, for thousands of years, humans have shaped the evolution of various animals and plants by systematically breeding those with desired characteristics, producing crops, livestock, companions, etc.
Natural selection was not widely accepted at first
While evolution (i.e. descent with modification/common descent) was soon accepted, natural selection as the primary cause was not. Several objections were raised, including:
– No new species had been produced via artificial selection, only varieties.
– Precursors of complex organs (e.g., the eye) are unlikely to have been advantageous.
– Ongoing debate about the earth not being sufficiently old.
– Natural selection will exhaust variation, halting further evolution.
– Direct evidence was lacking.
Example #1: Batesian mimicry (observational evidence)
Henry Walter Bates surveyed the Amazon rainforest with Wallace in 1848. Bates described situations in which a presumed palatable butterfly species gained protection from predators by resembling an abundant unpalatable species; later became known as ‘Batesian mimicry.’
Misconceptions about evolution
1) Natural selection is not goal-driven nor progressive.
2) Natural selection does not act ‘for the good of the species.
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3) Natural selection does not result in perfection.
Evolution vs. creationism
Creationism is the belief that nature and the universe originated from supernatural acts of divine creation; intelligent design is a pseudo-scientific rebranding of creationism.
Evolution and religion
Many scientists see no conflict between evolution and religious faith; a common view is that science and religion are separate domains.
Who developed the concept of Scala Naturae?
Aristotle.
What major idea did James Hutton introduce?
The concept of uniformitarianism, suggesting that geological processes operate over long periods.
What is Lamark’s mechanism for evolution?
The inheritance of acquired characters, suggesting traits gained during an individual’s life are passed to offspring.
Mary Anning
Learned paleontology because her family collected and sold fossils.
* LONG list of important discoveries (e.g., first correctly identified ichthyosaur skeleton, played a key role in showing that coprolites are fossilized feces).
What are the critical ingredients for natural selection?
1) Variation in traits
2) Non-random association between traits and reproductive success
3) Heritability of traits
