The Theory of Evolution Chapter 15 The Theory of Evolution

& Evidence for Evolution 15-1 Natural Selection & Evidence for Evolution The idea that life evolves was first Proposed by Lucretius 1900 years ago!

His idea was not fully considered until The middle of the 1800’s. In 1859, the English naturalist Charles Darwin published convincing Evidence that species evolve, and He proposed a reasonable mechanism Explaining how evolution occurs.

Like all scientific theories, the theory Of evolution has developed over Decades of experimental data. Today almost all scientists accept That evolution is the basis for the Diversity of life on Earth.

The theory of evolution has 4 parts: Variation exists with the genes of Every population of species (the results of mutation) 2) In a particular environment, some Individuals of a population or species Are better suited to survive and Have more offspring than others.

3) Over time, the traits that make Certain individuals of a population Able to survive and reproduce Tend to spread in that population. 4) There is clear proof from fossils And many other sources that living Species evolved from organisms That are extinct.

Naturalist for the naval voyage of The HMS Beagle. In 1831, Darwin became the Naturalist for the naval voyage of The HMS Beagle. The purpose of the voyage was to Survey the coast of South America.

During his voyage on the Beagle, Darwin found evidence that challenged The traditional belief that species Are unchanging. As Darwin visited the many places On his voyage, he saw things that Seemed as if they could only be Explained by a process of gradual change.

On the Galapagos Islands, Darwin Discovered different varieties of Finches that had different beaks. The birds looked similar, but had Evolved beaks that suited the Environment where they ate.

When Darwin returned from his Voyage, he continued his lifelong Study of plants, animals, and geology. He didn’t report his findings called “evolution” until much later.

After reading an essay by Thomas Malthus, Darwin made a key association, Individuals that have physical or Behavioral traits that better suit Their environmental are more likely To survive and reproduce than those That do not have such traits.

Darwin called this process by which Populations change in response To their environment, natural selection. The changing of a species that results In its being better suited to its Environment is called adaptation.

In 1859, Darwin finally wrote down His ideas of evolution and natural Selection in a book called “On the Origin of Species by Means of Natural Selection” Many people were deeply disturbed by It, including the church because it Hints that humans may have evolved from apes.

Darwin’s ideas have been updated… Natural selection causes change Within population. Such as, broccoli, cauliflower, Brussels sprouts, and cabbage all Come from the same plant!

In other words, natural selection Causes the frequency of certain Alleles in a population to increase Or decrease over time. Isolation leads to species formation.

Isolation is the condition in which 2 populations of the same species Cannon breed with one another. This happens all the time, and is why There are many different types of Squirrels, and is the reason that Darwin saw different types of The same bird!

Extinction leads to species replacement. Over long periods of time, events such As climate changes and natural Disasters result in some species Becoming extinct, which means That they disappear permanently.

15-2 Mechanisms of Evolution

Fossils provide an objective record Of evolution. A fossil is the preserved or Mineralized remains or imprint Of an organism that lived long ago.

Today Darwin’s theory is almost Universally accepted, based on a Large body of supporting evidence, Most scientists agree on the Following 3 points… 1) Earth is about 4.5 billion years old. 2) Organisms have inhabited Earth for Most of its history. 3) All organisms living today evolved From earlier, simpler life-forms.

Although the fossil record will never Be complete, it presents strong Evidence that evolution has Taken place. Paleontologists, scientists that study Fossils, can determine that age of Fossils fairly accurately by using Radiometric dating.

Biological molecules contain a record Of evolution. A common ancestor is a species From which 2 or more species Have diverged. A phylogenetic tree shows how organisms are related through evolution.

Anatomy and development Suggest common ancestry. Comparisons of the anatomy of Different types of organisms often Reveal basic similarities in Body structures.

For example, sometimes bones (or other structures) are present In an organism but are reduced in Size and either have no use or Have a less important function. Such structures are considered to be Evidence of an organism’s Evolutionary past.

These structures are called Vestigial structures.

Does evolution occur in spurts? The model of evolution in which Gradual change over a long period of Time leads to species formation Is called gradualism. The model of evolution in which periods Of rapid change in species is separated By periods of no change is called Punctuated equilibrium.

Darwin wrote: “Can we doubt… that Individuals having any advantage, However slight, over others, would Have the best chance of surviving And of procreating their kind?”

There are 5 main elements to Natural Selection… 1) All species have genetic variation. 2) The environment presents many Different challenges to an individual’s Ability to reproduce.

3) Organisms tend to produce more Offspring than their environment Can support; thus, individuals of a Species often compete with One another to survive. 4) Individuals within a population that Are better able to cope with the Challenges of their environment tend To leave more offspring than those Less suited to the environment.

5) The traits of the individuals Best suited to a particular Environment tend to increase In a population over time.

The key lesson scientists have learned About evolution is that the Environment dictates the direction And amount of change. A well studied example of natural Selection in action is Industrial melanism.

Industrial melanism is the darkening Of populations of organisms over Time in response to industrial pollution. The best known case is the European Peppered Moth.

The formation of new species Begins with small changes. The accumulation of differences Between groups is called divergence. Biologists call the process by which New species form speciation.

Overtime, populations of the same Species that differ genetically Because of adaptations to different Living conditions become what Biologists call ecological races. Eventually races may become so Different that they can no longer Interbreed successfully, biologists Then consider them a new species.

What keeps a new species separate? Reproductive isolation is the inability Of formerly interbreeding groups To mate or produce fertile offspring. This may happen due to geographical Reasons, or environmental reasons.

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