Questions addressed by Evolutionary Biology

Why are there so many different kinds of organisms?

Why are there so many species of flies and so few species of elephants?
How have they become good at what they do? Find food, mates, avoid predators?
What is related to what? And where do new species come from?
How old are they?

Charles Darwin was a man who found himself at the right place at the right time or the wrong place at the wrong time, depending on how you look at it. While he suffered seasickness and intestinal parasites (Chagas' disease) that would weaken his health for the rest of his life, he certainly considered his voyage as the most important thing that ever happened to him.

. The voyage of the HMS Beagle and Darwin's collections, observations and publications related to its five-year journey have perhaps affected human thinking in ways that no other scientific discoveries have. His Origin of Species and Descent of Man placed humans right smack in the middle of the animal world, at the top, perhaps, but there unmistakably.

. Not only did his ideas clash with theological and scientific thinking at the time, they made people uncomfortable. The thought that humans could be derived from primates didn't (and still doesn't) sit well with many people. (We can't be animals, can we?)

. In the years since Darwin's publications, scientists have mounted a considerable body of evidence to support the theory of evolution. Nonetheless, if you have any doubts as to your thinking about the evidence for evolution, I would encourage you to examine some of the creationist/evolutionist web sites (on both sides of the issue) and determine for yourself.

. What you should be able to distinguish within these debates is the difference between evolution itself (a gradual change in species with time) and the mechanisms of evolution (natural selection, kin selection, group selection, etc.). These are two different lines of scientific inquiry.

. That evolution has occurred on our planet would be very difficult to argue against, based on a considerable amount of fossil, zoological and molecular evidence. How evolution occurs (whether it occurs by some rational process or divine intervention) is where most of the debate is focused.

. Scientists believe that many different mechanisms of evolution occur rather than a single mechanism (i.e. survival of the fittest). And because people perceive this area of evolutionary research as the weakest (in terms of scientific evidence), that is where they usually attack.

Ch 20-21
Darwin
Darwin was not the originator of the concept of evolution
HMS Beagle voyage 1831-1836
Saw evidence of past organisms (fossils) similar to modern extant organisms -Argentina
Fossils high up in the Andes, Galapagos

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•Evolution
•The first convincing case for evolution was published in a book, On the Origin of Species by Means of Natural Selection, by Charles Darwin on November 24, 1859.
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•·      Made two major points:
•1. Species evolved from ancestral species and were not specially created.
•2. Natural selection is a mechanism that could result in this evolutionary change

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•Western culture resisted evolutionary views of life
•The impact of Darwin's ideas partially depended upon historical and social context.
•Darwin's view of life contrasted sharply with the accepted viewpoint:
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•the Earth was only a few thousand years old and was populated by unchanging life forms made by the Creator during a single week.
•Thus, On the Origin of Species by Means of Natural Selection not only challenged prevailing scientific views, but also challenged the roots of Western culture.

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•Many Greek philosophers believed in the gradual evolution of life. However, the two that influenced Western culture most, Plato (427 - 347 B.C.) and his student Aristotle (384 - 322 B.C.), held opinions which were inconsistent with a concept of evolution.

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•Plato, whose philosophy is known as idealism (essentialism), believed that there were two coexisting worlds:
•Aristotle believed that organisms range from simple to complex, he believed that they could be placed on a scale of increasing complexity (scala naturae); on this ladder of life, each form had its allotted rung and each rung was occupied.
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•·In this view of life, species are fixed and do not evolve.
•The scala naturae view of life prevailed for over 2000 years.

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•The creationist-essentialist dogma that species were individually created and fixed became embedded in Western thought as the Old Testament account of creation from the Judeo-Christian culture fortified prejudice against evolution. ·

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•·Natural Theology, a philosophy that the Creator's plan could be revealed by studying ,nature, dominated European and American biology even as Darwinism emerged.
•·For natural theologians, adaptations of organisms were evidence that the Creator had designed every species for a particular purpose.
•Natural theology's major objective was to classify species revealing God's created steps on the ladder of life.

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•Carolus Linnaeus (1707 - 1778), a Swedish physician and botanist, sought order in the diversity of life.
•Known as the father of taxonomy - the naming and classifying of organisms - he developed the system of binomial nomenclature still used today

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•Linnaeus, a natural theologian, found order in the diversity of life with his hierarchy of taxonomic categories.
•The clustering of species in taxonomic groups did not imply evolutionary relationships to Linnaeus, since he believed that species were permanent creations.
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Gradualism=Principle that profound change is the cumulative product of slow, continuous processes.
•Uniformitarianism=Theory that geological processes are uniform and have operated from the origin of the Earth to the present.

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•Lamarck (1744-1829) developed and published (1809) a comprehensive model which attempted to explain how life evolved.
•Envisioned many ladders of life which organisms could climb (as opposed to Aristotle's single ladder without movement).

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•Although his mechanism of evolution was in error, Lamarck deserves credit for proposing that:
•· Evolution is the best explanation for both the fossil record and the extant diversity of life.
•· The Earth is ancient.
•Adaptation to the environment is a primary product of evolution.

Ch 20-21
•Darwin ---born 1809
Charles studied under the Reverend John Henslow, a botany professor at Cambridge, and received his B.A. degree in 1831.
Professor Henslow recommended him to Captain Robert FitzRoy who was preparing the survey ship HMS Beagle for an around the world voyage.

•Descent with Modification
•Natural Selection and Adaptation
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•The Voyage of the Beagle
•The HMS Beagle, with Darwin aboard, sailed from England in December 1831.
•The voyage's mission was to chart the poorly known South American coastline.
•While the ship's crew surveyed the coast, Darwin spent most of his time ashore collecting specimens of the exotic and diverse flora and fauna.
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•While the ship worked its way around the continent,Darwin observed the various adaptations of plants and animals
•Darwin noted the following:

•The South American flora and fauna were distinct from the flora and fauna of Europe.
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•·   Temperate species were taxonomically closer to species living in tropical regions of South America than to temperate species of Europe.
•The South American fossils he found (while differing from modern species) were distinctly South American in their resemblance to the living plants and animals of that continent.
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•·Most animal species on the Galapagos are unique to those islands, but resemble species living on the South American mainland.
•· Darwin collected 13 types of finches from the Galapagos, and although they were similar, they seemed to be different species.
• Some were unique to individual islands.
• Others were found on two or more islands that were close together.
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•By the early 1840's, Darwin had formed his theory of natural selection as the mechanism of adaptive evolution, but delayed publishing it.
•In 1844, Darwin wrote a long essay on the origin of species and natural selection but did not publish it.
•Influences on Darwin were Lyell’s Principles of Geology and Malthus’s An essay on the principle of populations
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•In June 1858, Darwin received a letter from Alfred Wallace who was working as a specimen collector in the East Indies containing Wallace's own theory of-natural selection which was almost identical to Darwin's.
•Charles Lyell and a colleague presented Wallace's paper along with excerpts from Darwin's unpublished 1844 essay to the Linnaean Society of London on July 1, 1858.

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•Darwin finished The Origin of Species and published it the next year.
•Darwin is considered the main author or the idea.
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•
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•Darwin's 5 observations:
•1. All species have such great fertility that their population size would increase exponentially if all individuals that were born would reproduce successfully.
•2. Most populations are normally stable in size except for seasonal fluctuations.
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•3. Natural resources are limited.
•4. Individuals of a population vary extensively in their characteristics; no two individuals are exactly alike.
•5. Much of this variation is heritable.

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•Darwin's metaphor for the history of life was a branching tree with multiple branching from a common trunk to the tips of living twigs, symbolic of the diversity of contemporary organisms.
•·       At each fork or branch point is an ancestral population common to all evolutionary lines of descent branching from that fork.
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•Species that are very similar share a common ancestor at a recent branch point on the phylogenetic tree.
•Less closely related organisms share a more ancient common ancestor at an earlier branch point.
• Most branches of evolution are dead ends since about 99% of all species that ever lived are extinct.

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•Subtleties of Natural Selection
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•Evidence from Fields of Biology
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•Biogeography=The geographical distribution of a species.
•Fossil Record

The Environment is the Chief Agent of Natural Selection
Variation exists, some is heritable
Not all variations are equally well suited to a particular environment
Changes in environment produce changes in selective pressures
Differential reproduction, the best adapted will survive best and produce offspring

Evolution of adaptive traits
Those traits that are adaptive, confer an advantage in that environment
Individuals with these traits gain more resources and are better able to reproduce than others lacking them
Differential reproduction = Fitness
Fitness = passing genes to the next generation
Ch 20-21
• Comparative Anatomy
• Homologous structures=structures that are similar because of common ancestry.
•Vestigial organs=Rudimentary structures of marginal or no use to an organism.
•Comparative Embryology
•Molecular Biology
•Darwinism and Mendelism
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•A population has a genetic structure defined by its gene pool’s allele and genotype frequencies.
•Hardy-Weinberg Theorem describes a nonevolving population.
•Microevolution is a generation-to-generation change in a population’s allele or genotype frequencies.
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5 conditions for Hardy-Weinberg
1. Very large population size
2. Isolation from other populations.
3. No mutations
4. Random mating
5. No natural selection.
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Genetic drift=changes in the gene pool of a small population due to chance.
•Bottleneck effect
•Founder Effect
• Gene Flow=
•Nonrandom mating

EARLY ANIMAL EVOLUTION
•Biologists at the University of California, San Diego have uncovered the first genetic evidence that explains how large-scale alterations to body plans were accomplished during the early evolution of animals.

EARLY ANIMAL EVOLUTION
•The scientists show how mutations in regulatory genes that guide the embryonic development of crustaceans and fruit flies allowed aquatic crustacean-like arthropods, with limbs on every segment of their bodies, to evolve 400 million years ago into a radically different body plan: the terrestrial six-legged insects.
EARLY ANIMAL EVOLUTION
•The achievement is a landmark in evolutionary biology, because it effectively answers a major criticism creationists had long leveled against evolution—the absence of a genetic mechanism that could permit animals to introduce radical new body designs.
EARLY ANIMAL EVOLUTION
•“How can evolution possibly introduce big changes into an animal’s body shape and still generate a living animal?
EARLY ANIMAL EVOLUTION
•Creationists have argued that any big jump would result in a dead animal that wouldn’t be able to perpetuate itself. And until now, no one’s been able to demonstrate how you could do that at the genetic level with specific instructions in the genome.”
EARLY ANIMAL EVOLUTION
•The UCSD team showed in its experiments that this could be accomplished with relatively simple mutations in a class of regulatory genes,
•known as Hox, that act as master switches by turning on and off other genes during embryonic development.
EARLY ANIMAL EVOLUTION
•Using laboratory fruit flies and a crustacean known as Artemia, or brine shrimp, the scientists showed how modifications in the Hox gene Ubx—
EARLY ANIMAL EVOLUTION
•which suppresses 100 percent of the limb development in the thoracic region of fruit flies,
•but only 15 percent in Artemia—would have allowed the crustacean-like ancestors of Artemia, with limbs on every segment,……
EARLY ANIMAL EVOLUTION
•to lose their hind legs and diverge 400 million years ago into the six-legged insects!
•This kind of gene is one that turns on and off lots of other genes in order to make complex structures,” “What we’ve done is to show that this change alters the way it turns on and off other genes.

EARLY ANIMAL EVOLUTION
•That’s due to the change in the way the protein produced by this gene functions.
•The change in the mutated protein allows it to turn off other genes.

EARLY ANIMAL EVOLUTION
•The Hox genes in fruit flies that control the placement of the head, thorax and abdomen during development are a generalized feature of all animals, including humans.
EARLY ANIMAL EVOLUTION
•Before the evolution of insects, the Ubx protein didn't turn off genes required for leg formation.
•And during the early evolution of insects, this gene and the protein it encoded changed so that they now turned off those genes required to make legs, essentially removing those legs from what would be the abdomen in insects.
EARLY ANIMAL EVOLUTION
•A mutation in the Ubx gene and changes in the corresponding Ubx protein can lead to such a major change in body design undercuts a primary argument creationists have used against the theory of evolution in debates and biology textbooks.
EARLY ANIMAL EVOLUTION
•The word evolution may refer to many types of change.
•Evolution describes changes that occur within a species. (White moths, for example, may evolve into gray moths).
•This process is microevolution, which can be observed and described as fact.
EARLY ANIMAL EVOLUTION
•Evolution may also refer to the change of one living thing into another, such as reptiles and birds.
•This process, called macroevolution, has never been observed and should be considered a theory.
EARLY ANIMAL EVOLUTION
•The creationists’ argument rests in part on the fact that animals have two sets of chromosomes and that in order to get big changes, you’d need to mutate the same genes in both sets of chromosomes.
•.
EARLY ANIMAL EVOLUTION
•It’s incredibly unlikely that you would get mutations in the same gene in two chromosomes in a single organism.
EARLY ANIMAL EVOLUTION
•But in our particular case, the kind of mutation that’s in this gene is a so-called dominant mutation, so you only need to mutate one of the chromosomes to get a big change in body plan.

EARLY ANIMAL EVOLUTION
•The discovery of this general mechanism for producing major leaps in evolutionary change has other implications for scientists.
•It may provide biologists with insights into the roles of other regulatory genes involved in more evolutionarily recent changes in body designs.

Colp says that Darwin even experienced an "identity crisis" as a result of his emotional turmoil.
Colp decided that the physical problems started when Darwin began his theorizing, and worsened thereafter. Colp believes it was this guilt and ambivalence that kept Darwin for years from writing his book, until he did it to keep Wallace from obtaining prior credit ahead of himself.