Darwin’s Theory Darwin was not the first to consider evolution as a process, but he did come up with the first effective explanation for how it happens. In a 1-2 page Word document, describe Darwin’s theory of evolution by natural selection. Provide biological examples of Darwin’s work that led him to establish his theory. Explain how this theory was a major advance over prior ideas as to how organisms changed over time. Please reference your textbook for information. Course textbooks can be found on the Syllabus and Textbooks page of this course via the top navigation bar.
Darwin’s Theory
Darwin was not the first to consider evolution as a process, but he did come up with the first effective explanation for how it happens. In a 1-2 page Word document, describe Darwin’s theory of evolution by natural selection. Provide biological examples of Darwin’s work that led him to establish his theory. Explain how this theory was a major advance over prior ideas as to how organisms changed over time.
Please reference your textbook for information. Course textbooks can be found on the Syllabus and Textbooks page of this course via the top navigation bar. CORE SKILL: stating natural selection PRECISELY. Most students can gesture at “survival of the fittest” and almost all of them then misstate the mechanism. The precision is the assignment.
THE ARGUMENT IN ITS PROPER LOGICAL FORM — four premises and a conclusion that follows necessarily:
1. VARIATION: individuals within a population differ in their traits.
2. HERITABILITY: some of that variation is heritable — passed from parent to offspring.
3. OVERPRODUCTION / STRUGGLE FOR EXISTENCE: organisms produce more offspring than can survive to reproduce, given finite resources (Darwin took this from MALTHUS, and citing that intellectual debt is a nice touch).
4. DIFFERENTIAL REPRODUCTIVE SUCCESS: individuals whose heritable traits better suit the current environment leave, on average, MORE OFFSPRING.
CONCLUSION: the frequency of those traits increases in the population over generations. That is evolution by natural selection — and note that it is a DEDUCTIVE argument. Grant the premises and the conclusion is unavoidable, which is what made it so powerful.
THE MISCONCEPTIONS YOU MUST AVOID (and which the grader is watching for):
— “FITNESS” DOES NOT MEAN STRENGTH OR HEALTH. It means REPRODUCTIVE SUCCESS — the number of offspring contributed to the next generation. A sickly organism that reproduces prolifically is FITTER, technically, than a magnificent specimen that never breeds.
— EVOLUTION IS NOT PURPOSIVE. Organisms do not evolve traits BECAUSE they need them. Giraffes did not stretch their necks and pass the stretching on — that is LAMARCK’s inheritance of acquired characteristics, which is what Darwin displaced. Variation arises RANDOMLY (via mutation and recombination); selection acts on it NON-randomly. Getting this right — RANDOM VARIATION, NON-RANDOM SELECTION — is the single sharpest thing you can say.
— SELECTION ACTS ON INDIVIDUALS; EVOLUTION HAPPENS TO POPULATIONS. An individual does not evolve.
— Evolution is not progressive and has no goal or ladder.
BIOLOGICAL EXAMPLES (the prompt requires them — choose ones you can explain mechanistically, not just name):
— ANTIBIOTIC RESISTANCE: the best example available, because it is observable, medically urgent, and illustrates every premise. Random mutation produces resistance in a few bacteria; antibiotic exposure kills the susceptible; the resistant survive and reproduce; resistance frequency rises. NOTE THE COMMON ERROR TO AVOID: the antibiotic does not CAUSE the resistance mutation — it SELECTS for a variant that already existed. This is exactly the point where most students slip into Lamarckism.
— PEPPERED MOTHS (industrial melanism): allele frequency shifting with soot-darkened bark, then shifting back with clean-air legislation.
— DARWIN’S FINCHES: beak morphology tracking seed availability across drought years (the Grants’ long-term Galápagos work is the classic real-time documentation).
— SICKLE CELL: HETEROZYGOTE ADVANTAGE — the trait persists despite being harmful in homozygotes because carriers are protected against malaria. This is the best example because it shows that selection is CONTEXT-DEPENDENT: the same allele is beneficial or lethal depending on the environment.
ALSO WORTH INCLUDING: Darwin’s evidence (biogeography, homologous structures, fossil record, artificial selection as an analogy) and the modern synthesis (Mendelian genetics supplied the mechanism of inheritance that Darwin lacked — he had no idea how heredity worked, which was the great gap in his theory).
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