EvolutionDARWIN

Fact: Evolution= living things change over time. In 1859, Charles Darwin published The Origin of Species by Means of Natural Selection.—challenged the scientific views of

the time including the belief that the earth was just 6,000-10,000 years old and populated by unchanging life forms individually made during the one week that the Creator formed the entire universe.

Hutton: a geologist who explained the various land forms on earth today (canyons, fossils, etc.) as having arisen slowly as gradualism. Ex: he proposed that canyons formed by rivers cutting through rocks slowly.

Lyell: a geologist who developed the idea of uniformitarianism. Uniformitarianism: an idea that stated the geological processes have not changed over time. Ex: the forces that eroded

mountains in the past are the same ones working today.

Lamarck: first to suggest a model to explain how life evolved. By comparing current living species to fossil forms, he could see a chronological series of older to younger fossils leading to modern day species.

On the lowest “rungs of the ladder” were microscopic organisms, which Lamarck thought arose via spontaneous generation from nonliving material. At the top of the evolutionary ladder were complex plants and animals.

Lamarck was remembered for two ideas:1) His idea of “use and discuss”: the idea that if you use a body part a lot that body part will become larger and stronger, if

you don’t use a body part it will deteriorate. Ex: a giraffe had a short neck and it got longer by stretching it to reach leaves on high branches.

2) His belief of inheritance of acquired characteristics: modifications an organism acquires during his life can be passed onto offspring. So the long neck of the giraffe evolved gradually over many generations of stretching higher and higher to reach branches and then was passed onto offspring. Today we know acquired characteristics didn’t change genes and are not passed onto children, but Lamarck was a visionary in his time.

In 1831, Darwin asked to voyage around the world in a ship called the HMS Beagle—the mission of the voyage was to chart the South American coastline, but Darwin was to observe, record, and collect thousands of exotic faunas and floras.

He was especially interested in the fauna of the Galapagos Islands: islands of relatively recent volcanic origin west of S.A. Most of the animals on the islands live nowhere else in the world, bearing resemblance to species living on the mainland

of S.A. It was as though the islands were colonized by plants and animals that strayed from the mainland and then

diversification on the different islands. Darwin also collected 13 types of finches that were similar but different species—the most striking difference among

these birds was their beaks and what they ate. One species has a large beak adapted to cracking seeds, another had a beak to grasp insects, another used a small twig as

a tool to probe for wood-boring insects, etc. Darwin began to view the origin of species and adaptation to new environments as related processes. Ex: if a

geographical barrier like a channel separated 2 islands-isolating 2 populations of a single species, the populations would diverge more and more to adapt to local environmental conditions. Then over time, the 2 populations would be 2 separate species.

Species: sharing anatomical characteristics, members can interbreed, and produce fertile offspring. Wallace: developed a similar theory of natural selection—encouraged Darwin to publish his essay on The Origin of

Species; Darwin receives credit today for his ideas on evolution via natural selection. Darwin believed all organisms descended from a single common ancestor and, over millions of year, accumulated

diverse modification or adaptations to fit their environment. In the first publishing of his book, he didn’t use the term evolution—he called it “descent with modification. “ Ex: tigers and lions both descending from a similar ancestor along the “tree of life”—where each branch shows lineage.

D (domain)> K (kingdom)> P (phylum)> C (class)> O (order)> F (family)> G(genus)> S (species) Darwin’s main points on Natural Selection:

1) Production of more individuals than the environment can support leads to a struggle for existence. Ex: fish lay 1,000’s of eggs.

2) Survival in the struggle for existence is not random but depends on part of genetics. Those “best fit” to the environment survive and reproduce= “survival of the fittest.”

3) The unequal ability of some individuals to survive and reproduce will lead to gradual change in a population. = Evolution by natural selection.

Malthus: wrote an essay on human population, Darwin already recognized the struggle for existence when he read it—this essay spoke of human suffering that would occur as the human population increase faster than food supplies and other resources. The capacity to over reproduce is characteristic of all species.

Artificial selection: breeding of domesticated plants and animals for desired traits. Humans have modified many species over generations that now bear little resemblance to their wild ancestors.

So if humans can cause so much change via artificial selection, Darwin reasoned natural selection should also bring about gradual change eliminating less favorable variations over 100’s to 1000’s of generations.

Population: smallest unit that can evolve; it is a species that can interbreed and shares a common geographical area.

Evolution is not measured by individuals; it is variations in populations over many generations.

Natural selection: it is situational; it is a favorable adaptation in one situation may be useless or harmful in different circumstances.

The environment doesn’t create variations in a population. Both mutations (arise by chance) and genetic recombinations

(crossing over, law of independent assortment) are responsible for variation. If they are favorable, they enhance an organism’s reproductive success and are passed onto offspring.

Evidence of Evolution:1) Biogeography: Darwin documented evolution mainly by evidence from the geographical distribution of species. Ex:

islands have many endemic species (found only there), yet they resemble mainland species.2) Darwin based his observations on the fossil record. Paleontologists have discovered many transitional/

intermediate fossils to modern species. While Darwin used these 2 sources as proof of evolution today we use other sources as well.

3) Homologous structures are also evidence for evolution. Many of the same anatomical structures are similar between different organisms. Ex: the forelimbs of humans, cats, whales, bats, and all other mammals have many of the same skeletal elements but very different function. It makes no sense to have similar infrastructure unless they all descended from a common ancestor.

Vestigial organs: some other homologous structures are like this; they are historical remnants of structures that had importance in ancestors. Vestigial organs are reduced versions of organs and would be wasteful to continue providing blood, nutrients, and space to organs that no longer have major functions. Ex: appendix, coccyx (tail bone), wisdom teeth, pinky toe, body hair, ear muscle, males’ nipples.4) Closely related species go through similar

stages of embryonic development. Ex: all vertebrate embryos, including humans, go through a stage where they have gills/ pharyngeal pouches, post anal tail, webbed hands and feet.

5) Molecular biology supports relationships between species reflected in similar DNA and proteins. All life forms are related to some extent through branching descent from the earliest organisms. Even humans and bacteria have some proteins in common.

A common genetic code shared by all life forms is evidence of the branching of the tree of life ever since the code’s beginning in an early life form.

Some people dismiss Darwin’s ideas as “Just a theory”. This is flawed because it fails to separate the idea that modern species did indeed evolve from ancestral forms and that natural selection is the main mechanism for this evolution. To biologist, evolution is a FACT. The theory part of it is the mechanism of natural selection (punctuated equilibrium). Even now scientists are questioning whether natural selection alone accounts for evolution.

The image on the right often used as evidence that organisms have evolved: Whales and dolphins (mammals) have hip bones/ pelvic girdle. This is evidence that they evolved on land/ have legs and returned to water.