20.1 History of Evolutionary Concepts
Key Takeaways
Lamarck explained change by use and disuse and by inheritance of acquired characteristics; the giraffe-neck story is the classroom example, and it is not the accepted mechanism.
Darwin and Wallace proposed natural selection, and Darwin published On the Origin of Species in 1859.
Darwin's case used variation among individuals, artificial selection by breeders, and the fact that more offspring are born than survive.
The modern synthesis joins Mendelian inheritance with natural selection.
Fitness means relative reproductive success, not athletic strength, and a bodybuilder's trained muscles are not passed to children as genes.
20.1 History of Evolutionary Concepts
History items compare mechanisms. They ask who proposed which claim, what the classroom story means, and what fitness measures. Sort each stem by where the change happens: inside one lifetime, or across generations because some heritable variants leave more offspring.
A question older than genetics
Living things vary, and fossils often differ from living species, but the exam contrast is between two mechanisms. One says a change acquired during an individual lifetime is inherited. The other says a population changes because individuals already differ in heritable ways and some of those individuals leave more offspring.
Lamarck on use, disuse, and acquired characteristics
Jean-Baptiste Lamarck, working in the early nineteenth century, offered a mechanism in which the individual changes and then passes that change on. Two phrases carry his name, and they belong together.
Use and disuse says that a part an animal uses heavily becomes larger or stronger, while a part it rarely uses shrinks or disappears across generations. Inheritance of acquired characteristics says that a change gained during life is passed to offspring. Use or disuse is the proposed cause of the lifetime change. Inheritance of acquired characteristics is the proposed route into the next generation.
The giraffe-neck story is the classroom example, and it is not the accepted mechanism. Ancestors stretch to reach leaves, the neck lengthens during life, and offspring inherit that longer neck. Stretching does not rewrite alleles in eggs and sperm. A callus or a practiced skill is the same kind of lifetime change. It is not packaged into gametes as a new gene.
The accepted account starts from heritable differences in neck length that already exist. Individuals that reached food left more offspring, so those alleles became more common. No individual passed on a stretch it performed. Lamarck still belongs in the history because he treated species as changeable, but his mechanism is not another name for Darwin's.
Darwin, Wallace, and the book of 1859
Charles Darwin and Alfred Russel Wallace independently proposed natural selection. Wallace's manuscript pushed Darwin to publish. Darwin's book, On the Origin of Species, appeared in 1859. Lamarck's proposal is earlier and uses a different mechanism.
Darwin built the case from observations a reader of his time could check.
- Individuals in a population show variation. Offspring are not copies of one another or of their parents.
- Artificial selection by breeders shows that choosing which individuals reproduce can shift a breed. Darwin's evidence was pigeon and livestock breeding. The breeder keeps variants that already appear and does not turn a lifetime stretch into a gene.
- More offspring are born than survive. Limited resources make reproduction unequal. Darwin took that idea from Thomas Malthus and applied it to other organisms.
Heritable variants that help an individual reproduce become more common. Darwin argued this without Mendel's rules. Blending inheritance would average the parents and erase variation, so the later genetic account had to keep differences intact from parent to offspring.
The modern synthesis and what fitness means
The modern synthesis joins Mendelian inheritance with natural selection. Genes pass as discrete factors rather than blending away. Mutation and recombination supply inherited differences, and selection changes how common they are. In the early and middle twentieth century, population geneticists and naturalists showed that Mendel's factors and Darwin's argument describe one process. The synthesis is later than 1859, and it is not a new name for the giraffe story.
Fitness in that framework means relative reproductive success. Compare how many offspring an individual leaves, offspring that themselves survive to reproduce, with the success of other individuals in the same population and the same environment. Fitness is not athletic strength, running speed, or muscle mass unless those traits change the number of descendants. A small plant that sets more viable seed than its neighbors has higher fitness there. A large animal that does not breed has low fitness. The comparison is always relative, and it is always local to an environment. A trait that raises fitness on one background can lower it when the background changes.
How to sort a history item
If a change caused by use during one life is inherited, the idea is Lamarck's. If individuals already vary and some leave more offspring, the idea is natural selection, published by Darwin in 1859. Breeders choosing parents are his artificial-selection evidence. Fitness as the strongest body should be replaced with relative reproductive success.
| Concept | Associated with | Claim the item is testing |
|---|---|---|
| Use and disuse; inheritance of acquired characteristics | Lamarck | A lifetime change is inherited by offspring |
| Natural selection | Darwin and Wallace; On the Origin of Species (1859) | Heritable variation plus unequal reproduction |
| Modern synthesis | Twentieth-century evolutionary biology | Mendelian inheritance joined with selection |
| Fitness | Population biology in that framework | Relative reproductive success, not strength |
A check before you choose
Use three questions on every history stem.
- Does the stem say a body part changed because it was used or unused during one life?
- Does the stem say offspring inherit that lifetime change as if it were a gene?
- Or does the stem say individuals already vary, and some leave more offspring?
The first two questions point to Lamarck. The third points to Darwin and Wallace. The year 1859 points to Darwin's book, not to Lamarck and not to the modern synthesis. The synthesis is the later joining of Mendelian genetics with selection.
Warning
Acquired characteristics such as a bodybuilder's muscles are not passed to children as genes. Training changes a body within one lifetime. It does not, by itself, place new alleles in that person's gametes. Lamarck is not another name for Darwin. They gave different accounts of how the next generation comes to differ from the last.
In a classroom story, ancestral giraffes stretch their necks to reach leaves, the neck lengthens during life, and offspring inherit that longer neck. Which idea does the story illustrate?
Inheritance of acquired characteristics, together with use and disuse, as proposed by Lamarck
Fitness measured only as relative reproductive success in a given environment
The modern synthesis, which joins Mendelian inheritance with selection
Natural selection as argued by Darwin and Wallace and published by Darwin in 1859
Which observations did Darwin use in the case published in On the Origin of Species in 1859?
A recessive phenotype frequency equals the recessive allele frequency itself.
Organs change by use and disuse, and those lifetime changes are inherited as genes.
Individuals vary, breeders change populations by artificial selection, and more offspring are born than survive.
Fossil lineages stay unchanged and then a whole new body plan appears in one individual.
A bodybuilder's children are said to inherit the parent's trained muscles as genes, and the parent is called the fittest person because those muscles are large. How should those two claims be judged?
Trained muscles are acquired characteristics and are not passed as genes, and fitness means relative reproductive success rather than strength.
Both claims are correct, because fitness means physical strength and trained muscles are inherited as genes.
The muscle claim matches the modern synthesis, which treats acquired strength as a Mendelian allele.
The muscle claim is correct inheritance, and Lamarck is another name for Darwin.
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