Biological Evolution Definition: “Change in the genetic composition of a population during successive generations (due partly to natural selection) and resulting in the development of new species” (Wesbter’s).
Biological Evolution The ancestors of the horse, for example, have undergone considerable change in physical size and proportions over the last 60 million years.
Biological Evolution The adult size, shape, bones, internal organs and many other physical and behavioural features have changed. The original Eohippus was thus a different “type of animal” (species) than the present day horse (Equus)
Such changes in body parts are the result of changes in genes. When nature “selects” the “fittest” for survival and reproduction, it is also selecting the fittest combination of genes to survive and reproduce. These come “packaged” in a creature’s body.
Evolution and Genes Thus Biological Evolution happens through the transmission of genetic characteristics from one generation to the next. Individuals who are the most genetically “fit”, survive to reproduce (called natural selection or “survival of the fittest”) and pass on their fit characteristics.
Evolution and Genes During Darwin’s time not much was known about genetics. But Darwin did know that variation existed. That was enough to establish that in every species only those individuals that had favourable variations would be more fit and thus live on and reproduce.
Evolution by Natural Selection Natural selection is not the same as evolution Natural selection is one cause of biological evolution. It is like an “engine” that drives evolution on.
Evolution by Natural Selection “Natural selection” is a metaphor which Darwin compared to “artificial selection” (the breeding of plants & animals). In “artificial selection”, humans “select” which individual plant or animal will reproduce. In natural selection, “nature” does this “selecting”.
In fact, Darwin begins his Origin by discussing the artificial selection (breeding) of pigeons. In this example, we can see how three radically different looking breeds of pigeon (Pouter, Jacobin and Fantail) have been produced by artificial selection from the original Wild Rock pigeon.
Natural & Artificial Selection Varieties of bananas produced by artificial selection
Natural & Artificial Selection
Natural Selection
Natural Selection is like a machine with 3 parts: 1. Variation The tendency for individuals in a species to differ slightly from their parents and from each other.
1. Variation
1. Variation The tendency for individuals in a species to differ slightly from their parents and from each other.
1. Variation
1. Variation
1. Variation
1. Variation The exact causes of variation were discovered only after Darwin’s death. The discovery was made by the Austrian monk Gregor Mendel, the father of modern genetics.
1. Variation One cause of variation is sex - the combining of the genetic material of male and female to create offspring. (Also called sexual recombination) Another cause was mutation - accidents to the genetic material Variation is NOT caused by population increase or by the environment or by use/disuse, etc…
1. Variation Variation means there are different degrees of fitness among individuals in a population of the same species. Some happen to be born with advantageous variations (giving them added fitness) and others not.
2. Geometrical Population Increase The tendency for a population of any given species tends to outstrip the available resources necessary to keep it alive.
2. Geometrical Population Increase The “principle of population” was first expressed by the British political economist, Reverend Thomas Malthus.
2. Geometrical Population Increase In the human world, Malthus said, population tends to increase at a “geometric” rate while resources increase only at an “arithmetic” rate.
2. Geometrical Population Increase Given this geometric rate of increase, part of the human population is bound to be poor or even die.
2. Geometrical Population Increase
2. Geometrical Population Increase This “struggle for survival” would leave only the “fittest” individuals to survive (those with favourable variations) and reproduce Thus: GPI + V = NS (natural selection also called “the survival of the fittest”).
2. Geometrical Population Increase By “fit” Darwin meant not just the “strongest” but those best adapted to the environment These would tend to leave more offspring behind than the less fit.
3. Deep Time Deep time is the theory that the earth – and life on it – have been around for much, much longer than previously thought.
3. Deep Time Given sufficient time (deep time) natural selection will have “weeded out” so many unfavourable variations and accumulated so many favourable variations that a new species will have developed from a previous ancestor.
3. Deep Time Evolution by Natural Selection thus required millions of years to transform small changes into big ones. But many naturalists believed that the Earth was only about 6,000 years old.
3. Deep Time The Irish Archbishop James Ussher (1581-1656) calculated the age of the earth according to what he believed the Bible indicated.
3. Deep Time According to Ussher the universe began on Sunday, 23 October 4004 BC at 9:00 AM. This was not enough time for evolution to have occurred
3. Deep Time But by the 19th century, the science of geology confirmed that the earth was actually millions of years old. Key was geologist Charles Lyell’s book Principles of Geology which Darwin had read on the Beagle.
3. Deep Time Thanks to Lyell and the science of geology, the earth – and life on it – were proven to be much older than anyone previously thought For Darwin deep time was a key to acceptance of his evolutionary theory which required a huge time scale.
3. Deep Time: The Grand Canyon
3. Deep Time: The Grand Canyon
3. Deep Time
3. Deep Time Another way of visualizing deep time Note the many periods of glaciation Note the changes in the shape and position of continents
Summary: Natural Selection Geometrical Population Increase (GPI) - causes “struggle for survival” (meaning only some individuals will live and reproduce)
Variation (V) - causes differences in fitness b/w individuals
- THUS:
- GPI + V = “survival of the fittest” (natural selection)
Summary: NS + Deep Time
Cast of characters
The End Written & Directed by Gabriel Tordjman
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