Lecture 1 - Evolution: The Central Unifying Concept of Biology

Question 1

Evolution

Answer 1

• The notion that living organisms change slowly from one form into another over time
• The central unifying concept of biology and affects almost all other areas of knowledge
• Considered to be one of the most influential concepts of Western thought
• Evolution has no purpose and is an inevitable outcome of interactions between organisms and their environment

Question 2

Jean-Baptiste de Lamarck (1744–1829)

Answer 2

• The earliest advocate of evolution
• First presented a mechanism of evolution — based on the inheritance of acquired characters
• Individuals alter their morphology and behaviour according to the environment that they are in and these changes are then transmitted to subsequent generations
• In other words, use and disuse alters the structure of organisms
• Lamarck is unjustly remembered mostly as someone who got the mechanisms of evolution wrong
• He was also responsible for introducing the term “evolution” to the scientific world

Question 3

Charles Robert Darwin (1809–1882)

Answer 3

• Provided the first comprehensive theory of evolution in his famous book “On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life” published in 1859

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Question 4

The Origin of Species

Answer 4

2 major theses

1. Organisms are product of a history of descent with modification from common ancestors
2. The principal mechanism of evolution is the natural selection of hereditary variations

Question 5

Evolutionary Biology

Answer 5

Branches into:

1. Evolutionary history (macroevolution):
2. Evolutionary mechanisms (microevolution):

The questions, methods, and training of biologists in these two fields have tended to be quite different; although both groups of investigators follow the overall approach of hypothesis- testing and use of the scientific method.

Question 6

Evolutionary History (Macroevolution)

Answer 6

• Primarily interested in determining the evolutionary relationships among organisms in terms of common ancestry
• Information on the evolutionary affinities of organisms can then be used to provide a basis for the classification of organisms
• The disciplines of systematics, biogeography, palaeontology, morphology and development, and molecular biology largely provide the data on which inferences on the evolutionary history of organisms are based using comparative approaches

Question 7

Evolutionary Mechanisms (Microevolution)

Answer 7

• Involves determining the particular mechanisms and processes responsible for evolutionary change
• This field largely concerns work at the population-level (i.e., population biology) and frequently involves experimental studies of the ecology and genetics of populations
• A particular focus of such microevolutionary work is to understand the functional significance of variation in particular traits found in organisms that are believed to be adaptations

Question 8

Microevolutionary investigations over last 30-50 years show…

Answer 8

• Populations contain genetic variation that arises by random (not adaptively directed) mutation
• Populations evolve by changes in gene frequency brought about by random genetic drift, gene flow and especially natural selection. Most adaptive genetic variants have individually slight phenotypic effects so that phenotypic changes are gradual
• Evolutionary diversification comes about by speciation, which ordinarily entails the gradual evolution of reproductive isolation among populations.
  these processes, continued for sufficiently long, give rise to changes of such great magnitude as to warrant the designation of higher taxonomic levels (genera, families, orders, etc.)

Question 9

Problems

Answer 9

Despite being the most important concept in biology, evolution is often poorly understood and has frequently been misinterpreted for economic, social, and scientific reasons

Question 10

Things to remember about evolution

Answer 10

• Individuals do not evolve or adapt to their environment, because an individual is born and dies without any change in its genetic makeup.
  Only populations evolve.
• Natural selection has no purpose, direction or goal, not even the survival of the species.
  Evolution and natural selection, like blizzards and gravity, just are!
• Some people have equated evolution with “progress” from “lower” to “higher” forms of life, but it is impossible to define any non-arbitrary criteria by which progress can be measured. The very word “progress” implies direction, if not advance towards a goal; but neither is provided by the blind, utterly impersonal mechanistic nature of evolution.
• Despite popular misconceptions, evolution is not directed towards the emergence of the “higher” or more “advanced” human species.
  Darwin reminded himself in his notebook never to say “higher” or “lower” in reference to different forms of life.
• Natural selection has been taken as a morally proper “law of nature”, and the apparent progress perceived in evolution has been used to justify a range of political, social, and moral causes from class struggle and social Darwinism to opposition to birth control and homosexuality. However the supposition that what is natural is good falls outside the realm of science.
• The theory of evolution has sometimes been called just a hypothesis or even mere speculation. This idea is based on a misunderstanding of the scientific use of the term theory which means “a statement of what are held to be the general laws, principles, or causes of something known or observed” (Oxford English Dictionary). Today, evolution is not a hypothesis but a fact.