SPI Biology · Genetics and Evolution

Evolution and Its Evidence

Evolution is the slow change of living things over many generations, explained by theories such as Darwin's natural selection and shown by evidence such as fossils and homologous organs.

All Genetics and Evolution notes

Why this matters

Four questions in the bank, two EASY and two MODERATE: who gave natural selection, who gave the germplasm theory, what a deep fossil tells us, and which set of organs is homologous. Two are theory-and-author pairs; two are about reading the evidence.

Concept 1 of 2: Theories of evolution and their authors

Each theory tried to answer one question: how do new kinds of living things arise? Lamarck said by use and disuse; Darwin said by nature choosing the fittest; de Vries said by sudden big changes. Learn each theory with its author.

Definition

Lamarck: inheritance of acquired characters (use and disuse of organs; the giraffe's long neck).
Charles Darwin: natural selection, survival of the fittest (book: On the Origin of Species, 1859).
August Weismann: germplasm theory. Only changes in the germ cells (sperm and egg) pass to offspring; changes in body cells do not. This went against Lamarck.
Hugo de Vries: mutation theory: new species arise by sudden large changes.
Mendel gave the laws of inheritance, not a theory of evolution.

Scientist	Theory
Lamarck	Inheritance of acquired characters
Charles Darwin	Natural selection Darwin's book: On the Origin of Species (1859).
August Weismann	Germplasm theory
Hugo de Vries	Mutation theory

A change a body acquires in life (a strong arm, a cut tail) is not passed on: Weismann's point against Lamarck.

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The same idea in a practice question:

Practice questionEasy

Example 1 · Genetics and Evolution · Evolution and Its Evidence

The theory of evolution of species by natural selection was given by

Darwin for every evolution question

Darwin gave natural selection only. The germplasm theory is Weismann's, the mutation theory de Vries's and acquired characters Lamarck's.

Mendel as an evolution theorist

Mendel worked out how traits are inherited. He gave no theory of how species change.

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Concept 2 of 2: Fossils, homologous and analogous organs

Evidence for evolution comes from what animals and plants left behind (fossils) and from their bodies today. Organs built the same way but used differently show a shared ancestor; organs used the same way but built differently do not.

Definition

Fossils: remains or traces of old organisms preserved in rock. Rock layers settle one on top of another, so deeper layers are older: a deep fossil is of an organism that lived long ago.
The age of a fossil can be found by carbon dating (radioactive carbon).
Homologous organs: same basic structure and origin, different jobs. The forelimbs of a frog, lizard, bird, bat, cow, whale and human share one bone pattern.
Analogous organs: same job, different structure and origin. The wing of a butterfly and the wing of a bird; also the wing of a bat and the wing of a bird, taken as wings.
Archaeopteryx, a fossil with feathers and teeth, links reptiles and birds.

Type	Structure	Job	Example
Homologous	Same	Different	Forelimbs of cow, duck, lizard, human Homologous: same build, different use.
Analogous	Different	Same	Wings of butterfly and bird

Homologous organs point to a common ancestor; analogous organs only to a common need.

Practice this conceptself-check · 4 quick reps

The same idea in a practice question:

Practice questionModerate

Example 2 · Genetics and Evolution · Evolution and Its Evidence

Select the set of homologous organs from the following:

Calling any two wings homologous

Wings do the same job, so two wings are analogous: a butterfly's and a bird's are built from different parts. Homologous organs are the ones with the same build but different jobs, such as forelimbs.

Thinking depth says nothing about age

Rock layers pile up over time, so the deeper the layer, the older the fossil in it.

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Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Reference tables (2)

Theories of evolution and their authors4 rows

Scientist	Theory
Lamarck	Inheritance of acquired characters
Charles Darwin	Natural selection Darwin's book: On the Origin of Species (1859).
August Weismann	Germplasm theory
Hugo de Vries	Mutation theory

A change a body acquires in life (a strong arm, a cut tail) is not passed on: Weismann's point against Lamarck.

Fossils, homologous and analogous organs2 rows

Type	Structure	Job	Example
Homologous	Same	Different	Forelimbs of cow, duck, lizard, human Homologous: same build, different use.
Analogous	Different	Same	Wings of butterfly and bird

Homologous organs point to a common ancestor; analogous organs only to a common need.

Watch out for (4)

Darwin for every evolution question
→ Theories of evolution and their authors
Mendel as an evolution theorist
→ Theories of evolution and their authors
Calling any two wings homologous
→ Fossils, homologous and analogous organs
Thinking depth says nothing about age
→ Fossils, homologous and analogous organs

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