Lamarck's Theory and Vestigial Organs

What you do

• Vestigial organs are remnants of features that served important functions in an organism's ancestors. Man has over a hundred of them.
• Darwin could not explain where variations come from. Modern genetics revealed their sources, and the modified theory is called Neo-Darwinism. Darwin is still regarded as the Father of Evolution.

Challenges to clear

• Sort all ten ideas into the correct theory.
• Fill Darwin's column with his four observations and his example.
• Fill the Lamarck's theory column — the claim that use and disuse are inherited.

The task

Two great explanations of how evolution happens. Sort each idea into the theory it belongs to.

What this lesson covers

• Lamarck's theory — Inheritance of acquired characters: Use and disuse: parts of the body used extensively become larger and stronger (This is the first of Lamarck's two principles, drawn from comparing living species with a series of older and younger fossils.); Parts that are not used deteriorate and become atrophied (The other half of use and disuse. Organs reduced in this way persist generation after generation as vestigial organs.); An organism can pass its own modifications on to its offspring (This is inheritance of acquired characters, the principle that gives Lamarck's theory its name.); The giraffe's neck and forelimbs grew long by constant stretching for high leaves (Lamarck's classic example. Ground level vegetation ran short, the giraffe took to feeding from trees, and constant stretching over many generations lengthened the neck and forelimbs.); Wisdom teeth, the vermiform appendix and the pinna in humans (These are the three vestigial organs Selina names, and they are explained by disuse: the wisdom teeth are hardly used for chewing, the appendix digests cellulose only in herbivores, and we cannot move the pinna to gather sound.)
• Darwin's theory — Natural selection: Overproduction: oysters lay 60 to 80 million eggs in a single spawn (Darwin's first observation. Far more offspring are produced than can possibly survive, yet numbers stay roughly constant.); Struggle for existence, because numbers multiply while food and space stay almost constant (Darwin's second observation. Competition may be within a species or between different species, for shelter, climate, food and breeding places.); Variation: no two individuals, even of the same parents, are exactly alike (Darwin's third observation. Without variations no change could occur, and there would be no possibility of evolution.); Survival of the fittest: nature selects only the suitable variations (Darwin's fourth observation. Nature selects the fittest and rejects the weaker individuals, and this selection is what he called natural selection.); The dark peppered moth replaced the light one on soot-blackened tree trunks (Industrial melanism in Biston betularia is the classic worked example. Birds picked off whichever variety was easier to see, so the better-hidden one survived and left more offspring.)

Hint

Table 14.1 sets the two theories side by side. Both say new species arise over a long period of time. They differ in what carries the change: Lamarck says characters acquired by use and disuse are inherited, Darwin says favourable variations already present in the population are selected.