Origin and Evolution of Life Questions

About Origin and Evolution of Life

Medium ~85 min study

Two questions run through this chapter, and they are among the oldest anyone has asked. How did life begin, and why are living things the way they are now rather than some other way? The answers offered here are scientific ones, built on evidence that can be examined rather than on assertion, and much of the chapter is concerned with what counts as evidence at all.

Two explanations are compared. Lamarck argued that an organism changes during its own lifetime through the use and disuse of its organs, and that these acquired characters pass to its offspring. Darwin argued differently: far more offspring are produced than can survive, they vary among themselves, and those best suited to their circumstances are the ones that live to reproduce. The difference between these two accounts is the single most examined idea in the chapter.

The rest of the material supplies the evidence. Fossils give a direct record of ancient life and can be dated by measuring radioactive decay. Homologous organs point to shared ancestry while analogous organs warn against reading similarity too quickly. Vestigial organs and embryological patterns add further support. Ethnobotany and astrobiology close the chapter by pointing outward, to traditional plant knowledge and to the search for life beyond the Earth.

What you'll learn

• State the principles of Lamarckism and the postulates of Darwinism and contrast the two.
• Distinguish homologous from analogous organs with examples.
• Identify vestigial organs and explain what they suggest about ancestry.
• State the biogenetic law and explain the terms ontogeny and phylogeny.
• Explain how fossils form and why they are evidence for evolution.
• Choose an appropriate dating method for a fossil of a given age.
• Define ethnobotany and astrobiology and name who coined the former.

Before you start

• Basic classification of plants and animals from earlier classes.
• An understanding of adaptation and of variation among individuals.
• Familiarity with the idea that characters are inherited from parents.

Origin and Evolution of Life explained

What this chapter covers

Lamarckism

Lamarck held that an internal vital force, the environment and new needs drive change in an organism. Organs that are used develop further while those that are not degenerate, and the characters so acquired during a lifetime are passed to the next generation. These are the main principles of Lamarckism, and the theory is remembered chiefly through the use and disuse of organs.

Darwinism and natural selection

Darwin's account rests on a few observations. Each species produces a large number of offspring, more than the environment can support, which leads to a struggle for existence. Individuals vary, and only the fittest survive to reproduce. Overproduction, struggle for existence, variations, survival of the fittest and the origin of species are the main postulates of Darwinism.

Evidences from comparative anatomy

Homologous organs share a basic structure and origin but perform different functions, as a bat's wing and a human hand do, and they indicate descent from a common ancestor. Analogous organs perform the same function but differ in structure and origin, as the wing of a bat and the wing of an insect do. Vestigial organs are degenerated and non functional remnants, such as the vermiform appendix and the caudal vertebrae.

Embryological evidence and the biogenetic law

Patterns in the development of embryos across different groups also point to evolutionary relationships. The biogenetic law expresses this by stating that ontogeny recapitulates phylogeny, meaning that the development of an individual repeats the evolutionary history of its race.

Fossils and their dating

Fossils are evidences of ancient life forms or ancient habitats preserved by natural processes, and palaeontology is the study of them. Their age is found by measuring radioactive decay. The radiocarbon method suits fossils of recent origin because carbon decays quickly, while the uranium lead and potassium argon methods are used for far older material. Archaeopteryx, the fossil bird, serves as a connecting link and supports the conclusion that birds evolved from reptiles.

Ethnobotany

Ethnobotany is the study of how particular groups of people, especially tribal communities, have traditionally used plants. The term was coined by J.W. Harshberger. The ethnobotanical importance of various plants is known through traditional knowledge passed down within these communities.

Astrobiology

Astrobiology, also called exobiology, is the science which looks for the presence of extra terrestrial life in the universe. The chapter mentions current work investigating ancient environments and the possibility of past life on Mars, together with the preservation of biosignatures in accessible geological materials.

Common mistakes to avoid

• Swapping homologous and analogous organs. Homologous share structure and origin; analogous share only function.
• Crediting the use and disuse theory to Darwin. It belongs to Lamarck; Darwin proposed natural selection.
• Stating the biogenetic law backwards. It is ontogeny that recapitulates phylogeny, not the reverse.
• Choosing radiocarbon dating for very ancient fossils. Carbon decays quickly, so it suits only recent material.
• Treating palaeontology as covering embryological and vestigial evidence. It deals with fossils alone.

Test yourself on these with the practice test, then check the worked reasoning in the solved MCQs.

Frequently asked questions

What is the difference between homologous and analogous organs?

Homologous organs have the same basic structure and the same origin but carry out different functions, as with a bat's wing, a human hand and the flipper of a whale. Analogous organs carry out the same function but differ in structure and origin, as with the wing of a bat and the wing of an insect. Homology indicates common ancestry; analogy does not.

What are the main principles of Lamarckism?

Lamarck proposed four connected ideas: an internal vital force present in organisms, the influence of the environment and of new needs, the use and disuse of organs, and the inheritance of acquired characters. Together these hold that changes an organism develops during its own lifetime are passed on to the next generation.

What are the main postulates of Darwinism?

Darwin's theory rests on overproduction, since each species produces far more offspring than can survive; the struggle for existence that follows; the variations that exist among individuals; the survival of the fittest, also called natural selection; and the origin of species that results from this process acting over long periods.

What does the biogenetic law state?

The biogenetic law states that ontogeny recapitulates phylogeny. Ontogeny means the development of an individual organism from fertilization onward, and phylogeny means the evolutionary history of its race. The law therefore holds that in developing, an individual passes through stages that reflect the evolutionary history of its group.

What are vestigial organs and why do they matter?

Vestigial organs are degenerated and non functional organs found in an organism, such as the vermiform appendix and the caudal vertebrae in human beings. They matter because a structure that serves no purpose is difficult to explain unless it was inherited from an ancestor in which it was functional, so they are treated as evidence of descent.

How are fossils dated?

Fossils are dated by measuring the decay of radioactive elements in or around them. The radiocarbon method is the best way of directly dating fossils of recent origin, because carbon decays comparatively quickly. For much older fossils the uranium lead method and the potassium argon method are used instead.

Why is Archaeopteryx considered a connecting link?

Archaeopteryx is a fossil that shows characters of both reptiles and birds at the same time. Because it combines features of two groups rather than belonging cleanly to either, it is treated as a connecting link between them and supports the conclusion that birds have evolved from reptiles.

What is ethnobotany?

Ethnobotany is the study of the way particular groups of people, especially tribal communities, have traditionally used plants for food, medicine and other purposes. The term was coined by J.W. Harshberger. The ethnobotanical importance of many plants is known only through this traditional knowledge, which is why recording it matters.