LECTURE                                MACRO  EVOLUTION

In this lecture you will learn about:

THE SCIENTIFIC THEORY OF EVOLUTION
Evolution is a SCIENTIFIC theory because it is testable.  Darwin wrote the book "On the Origin of Species"

Any "theory" that begins with a conclusion is NOT SCIENCE because it is NOT testable. 

Once again we need to talk about the observations that lead to a hypothesis. For a hypothesis to progress to a theory it needs both proof AND one or more mechanisms. 

So... we observe the sun rise in the east and set in the west.  The MECHANISM is that the earth rotates on its axis. 

The continents appear to "fit" together.  The mechanism is plate tectonics caused by sea floor spreading and subduction of plates. 

In the Galapagos, Darwin observed that all the finches looked alike except that their bills were different.  All finches seemed to have originated with only a couple birds that were blown in from the mainland.  Different bills are an adaption to different "foods".  Birds with different bills represent different species. 

 

Charles Darwin: 
1809: Born in Shrewsbury, Shropshire
1825: Goes to Edinburgh University to study medicine
1827: Joins Cambridge University to prepare to become a clergyman
1831: After graduation, joins HMS Beagle
1836: Returns to England and begins developing ideas on changeability of species
1838: Arrives at a sketch of evolution
1839: Marries Emma Wedgwood and moves to Kent
1858: Evolution theory announced in academic paper
1859: Publishes On the Origin of Species
1882: Dies on April 19 and is buried at Westminster Abbey

WHAT IS A SPECIES?
A species is defined as a group of organisms that breed naturally and produce fertile offspring.

All humans are one species.
All dogs are one species. 
Lions and tigers do not naturally breed in the wild.
Horses and donkeys dont either. 

There exists color variations within a species and this used to be called "races".  For example, Northern Flickers vary in color altho they are all one species and interbreed readily.  See wings at right. 

NO TWO SPECIES can occupy the same niche and habitat.  If they do, one will be driven to extinction by the more successful species. 


Detail of shaft color variation in wings of Colaptes auratus (Northern Flicker). From Burke Museum spread wing collection: 51239 and 58625.

 
THE CENTRAL THEORY AND FOUNDATION OF THE THEORY OF EVOLUTION 
1. NATURAL VARIATION
1. there is a NATURAL VARIATION in traits among the members of any group of organisms. This is due to 
a. the independent reassortment  of chromosomes during the second division in meiosis AND 
b. (to a lesser degree) crossing over in meiosis.

VARIATION is due to the accumulation of non-lethal mutations in alleles over vast periods of time. 

1. SELECTIVE ADVANTAGE that results in leaving more offspring
2. some one or more traits confer a selective advantage to a given population such that they LEAVE MORE VIABLE OFFSPRING. 

These two concepts ARE the two mechanisms of speciation. 

 

Natural selection is also NOT based simply on chance on a single individual or a "one shot deal"... rather selection works on populations, altho it works even better on small populations.  If the variation is not consistently selected for over very long periods of time a new species is unlikely to evolve.  

Natural selection IS NOT the "survival of the fittest."  It doesn't matter how "fit" the individual is,  if they don't leave offspring, they are genetically weeded out.

Stages in evolution leading to new species

 
VARIATION and ADVANTAGE,  BUT NOT SPECIATION
Genetic variation by itself is not evolution.  As long as all members of the population are likely to mate and produce viable offspring they are one species. 
 

So the moths show both variation AND selective advantage, but it doesnt lead to speciation. 

EXAMPLE:  A typical example seen recently is that of the peppered moth.
-- The moths have a natural variation in color, some light, some dark.
– in unpolluted or stands of light colored trees, the light colored moths will not be seen, will not be eaten, will be more likely to leave offspring.
– in polluted or dark colored stands of trees, the dark have the "selective advantage" in leaving offspring. 


 
VARIATION and ADVANTAGES THAT LEADS TO SPECIATION
Occurs when  interbreeding DOES NOT occur.   
1.     GEOGRAPHIC ISOLATION (Allopatric)
– a single species gets split into two groups that are geographically isolated from each other. 

Example is the a. Grand Canyon, it split a single species of squirrel into two groups.  These developed into two closely related but different species one on the north rim and one on the south rim of the grand Canyon. 
b. Darwins finches also shows this when compared to the species on the mainland
c.  Pangea splits up, Australia has only marsupials an older evolutionary stock while the rest of the continents evolved mammals

2.    BEHAVIORAL BARRIERS (Parapatric)
– speciation by female selection.  Particularly true of birds.  If the song and dance isnt right, no breeding.  Females always pick the males. 

Ring species is a connected series of neighboring populations that can interbreed with relatively closely related populations, but for which there exist at least two "end" populations in the series that are too distantly related to interbreed.

A classic example of ring species is the Larus gulls circumpolar species "ring". The range of these gulls forms a ring around the North Pole.

ring species
In this diagram, interbreeding populations are represented by coloured blocks. Variation along a cline may bend right around, forming a ring.
3.    NATURAL DISASTERS (Peripatric)
– a natural disaster that kills a large fraction of the population resulting empty "niches" that can be filled by a small pioneer population. 
... when islands are formed, like the Galapagos or the Hawaiian Islands. 

The founder effect refers to the loss of genetic variation when a new colony is established by a very small number of individuals from a larger population. The small population has a much smaller genetic variability and possibly a high incidence of detrimental genes. 

 


Simple illustration of founder effect. The original population is on the left with three possible founder populations on the right.
4. CHROMOSOME FUSION OR SPLITTING?

The Importance of Gene Rearrangement in Evolution: Evidence from Studies on Rates of Chromosomal, Protein, and Anatomical Evolution

Abstract: We have compared the relative rates of protein evolution and chromosomal evolution in frogs and mammals. The average rate of change in chromosome number has been about 20 times faster in mammals than in frogs. Whereas it takes only 3.5 million years, on the average, for a pair of mammal species to develop a difference in chromosome number, the corresponding period for frogs is 70 million years. In contrast, the rate of protein evolution in mammals has been roughly equal to that in frogs. The rapid rate of gene rearrangement in mammals parallels both their rapid anatomical evolution and their rapid evolutionary loss of the potential for interspecific hybridization. Thus, gene rearrangements may be more important than point mutations as sources for evolutionary changes in anatomy and way of life. 
http://www.pnas.org/content/71/8/3028.abstract

Structural Dynamics of Eukaryotic Chromosome Evolution

"Abstract: Large-scale genome sequencing is providing a comprehensive view of the complex evolutionary forces that have shaped the structure of eukaryotic chromosomes. Comparative sequence analyses reveal patterns of apparently random rearrangement interspersed with regions of extraordinarily rapid, localized genome evolution. Numerous subtle rearrangements near centromeres, telomeres, duplications, and interspersed repeats suggest hotspots for eukaryotic chromosome evolution. This localized chromosomal instability may play a role in rapidly evolving lineage-specific gene families and in fostering large-scale changes in gene order. Computational algorithms that take into account these dynamic forces along with traditional models of chromosomal rearrangement show promise for reconstructing the natural history of eukaryotic chromosomes."

http://stke.sciencemag.org/cgi/content/abstract/sci;301/5634/793

CHROMOSOME 1

http://www.dna-rainbow.org/species-comparison.html

 
RATE OF EVOLUTION
GRADUAL

— slow change in a species over very long periods of time
— the genes of a species drifts

They can become specialist, like cheetahs that run fast, but can only take small animals altho this is a ticket to extinction if the smaller animals decline or disappear

Another example are species of moths and orchids.. they are completely dependent on each other.  If one goes, they both go extinct.

– because gradualism is slow, finding all the "pieces", all the fossils of intermediate forms is difficult in the extreme. 
------ *** BECOMING A fossils means mostly being at the right place at the right time, leaving big pieces behind. one reason so many dinosaurs and so few itty bitty  mammals that were living at the same time.  HOWEVER, scientists are getting better at identifying itty bitty, including the fossils of BACTERIA ..  way coool.
– there is an extremely good gradualism record of clams/oysters cause they leave good fossils. 

PUNCTUATED EQUILIBRIUM

– several things contribute to "sudden" or "fast" speciation without many intermediate forms. 
 Mostly this is due to new niches opening up due to new uninhabited land masses or mass extinctions of one kind or another. 
 
 

MASS EXTINCTIONS
 

 


 
"BODIES" OF EVIDENCE, PROOFS 
1. FOSSIL RECORDS

 If we didnt have fossils we wouldnt know that in times past there were other shapes and forms.   Fossils show that there are extinct species.  The different layers show there are an uncountable number of species that have gone extinct. 

"For fossilization to take place, the traces and remains of organisms must be quickly buried so that weathering and decomposition do not occur. Skeletal structures or other hard parts of the organisms are the most commonly occurring form of fossilized remains (Paul, 1998), (Behrensmeyer, 1980) and (Martin, 1999). There are also some trace "fossils" showing moulds, cast or imprints of some previous organisms."
http://en.wikipedia.org/wiki/Evidence_of_common_descent

Fossil evidence can be radiometrically dated.

SOME FOSSILS ARE 

Amber contains some of the best preserved WHOLE living things.  Ice does a good job too. 


 
2.  COMPARATIVE ANATOMY 

to see larger image right click select view image

Figure 5a: The principle of homology illustrated by the adaptive radiation of the forelimb of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched.


 
3. COMPARATIVE BIOCHEMISTRY

"Universal biochemical organisation

All known extant organisms are based on the same fundamental biochemical organisation: genetic information encoded as nucleic acid (DNA, or RNA for viruses), transcribed into RNA, then translated into proteins (that is, polymers of amino acids) by highly conserved ribosomes. Perhaps most tellingly, the Genetic Code (the "translation table" between DNA and amino acids) is the same for almost every organism, meaning that a piece of DNA in a bacterium codes for the same amino acid as in a human cell. ATP is used as energy currency by all extant life."
 

4.  DNA COMPARISON

This has been a whole new area of evolution research looking at the drift in genes over time as a way of determining the age of species since they "separated" from a common ancestor
age of species since they "separated" from a common ancestor

a.  look at the sequence of the genes themselves and see how much change there is (medium fast change)

T. rex fossil has 'soft tissues'
Protein links T. rex to chickens
Molecular Analysis Confirms Tyrannosaurus Rex's Evolutionary Link To Birds
http://focus.hms.harvard.edu/2007/042007/proteomics.shtml

JUST HOW CLOSELY RELATED ARE WE TO OTHER LIVING THINGS?

– we have around twice as many genes as fruit flies
– we share about 50% of the same genes as bananas
– "Of the 5,000  best-known  human genes 75 percent  have matches in the C.   elegans, a tiny  worm." 
– "It has only 959 cells yet reproduces, grows into a mature adult, eats,  excretes and dies with many of the cellular interactions of other animals.
– the genes that are shared are "core" genes like those in mitochondria that make ATP,  cytochrome C, ubiquinone, ATPase, etc.  – the genes that direct DNA synthesis, DNA replication, cell division, all the "housekeeping" duties that EVERY cell has to perform.
http://www.pbs.org/wgbh/nova/genome/dna_sans.html

"We share 50% of our DNA with bananas…

It's true. Humans share 50% of their DNA with bananas. Apparently Steve Jones, Professor of Genetics at University College, London is credited with stating this information. Kind of freaky when you think about it. DNA (deoxyribonucleic acid) is what makes us all different, but the difference between us and the next species or even a fruit isn't as significant as you would think.

However, according to Penn State University, a human DNA sequence, if it were a half an inch of a twine, would stretch from New York to the the west coast of California. That makes that 50% seem all the more distant when you think of the whole number/complexity that the percent refers to.
 

Other DNA facts you don't need to know:
- A parent and child share 99.5% of the same DNA.
- We share 40-50% of our DNA with cabbages.
- Humans share 98% of their DNA with chimpanzees.
- Every human on earth shares 99% of their DNA with every other human.
- Identical twins share the exact same DNA - meaning their DNA is 100% identical.
- We share 60% of our DNA with a fruit fly.
- Researchers at Cambridge University are convinced that the mud worms not only share DNA with humans but that they are also our closest invertabrae relatives."
http://www.thingsyoudontneedtoknow.com/dnabananas.html

Any two human beings are no more than 0.1% different from each other .. ANY two people, any color, any ethnicity but any two chimps are >0.2%  different from each other. 

This means that chimps have been chimps LONG ENOUGH to drift genetically away from each other while humans are remarkable homogeneous.  The lack of variability points to both how recently we evolved AND that we came from a very small population, they say probably no more than 20,000 individuals.  Remember, the smaller the "founder" population the faster speciation can happen.

It may also point to a recent near extinction of humans. 

 

 
OBSERVATION OF SELECTION AT WORK: GENETIC DRIFT
1. viruses.. influenza

.... each year we gotta get a new flu shot cause the flu antigens have DRIFTED.  The exact sequence of the protein that gets the virus into the cell changes as the infection spreads across the world

---- flu is unusual in that it RECOMBINES with animal varieties of flu leading to changes in the infectivity.  The human immune system selects against common antigens and the only virus that "survives" is the one that is different enough it infects makes lotsa copies and gets sneezed out onto the next victim

2. bacteria and antibiotic resistance ... the GENES for resistance are there, when we use the antibiotic, we "select" for resistant bacteria
.... how to select

a. low doses of antibiotics.. like penicillin in cattle feed

b. don't use it long enough to kill all the bacteria (with the help of the host's immune system)

3. insects developing resistance to pesticides

... the only long term pesticides that are going to work are the natural viruses and bacteria that can mutate right along with the insects ... don't get 100% kill, but it keeps up at least.  Putting the Bt gene into the corn wont do that cause it isn't a real bacteria that can mutate along with the insect, it is just a gene in the plant

4.  Rabbits in Australia

.. myxovirus killed 98% of rabbits... those 2% survived (were resistant) and they reproduced, and the next time there was 68% killing .. the whole gene pool of the population is moving to a resistant genotype

 

REVIEW QUESTIONS:
Discuss the central theory and foundation of evolution.
What are the two basic mechanisms that must be present for natural selection to occur.
Give some examples of natural selection that can be easily observed.
Why is the "survival of the fittest" irrelevant?
Why does natural selection only work on population?
Where do the new genes come from that natural selection work on?
Why is genetic variation by itself NOT evolution?
Discuss the proofs or bodies of evidence of evolution.
What kind of conditions promote speciation.
Discuss the kind of environment or conditions that leads to slow or gradual speciation.  Give examples.
Discuss the kind of environment or conditions that leads to fast or punctuated evolution.  Give examples.
What is a population bottleneck and how does this contribute to faster speciation.
What is  a "founder effect".
Discuss DNA as a fossil record and how closely related we are to all living things.
Discuss how we can observe evolution at work.