Principles of Evolution

Darwin's 'dangerous idea' - descent with modification, or evolution by natural selection.

First, some definitions:
 Evolution:  Change in the genetic makeup of a population over time.
 Species:  Group of individuals that can interbreed in pecies.
 Natural Selection:  The mechanism by which genetic change
   occurs in natural populations in response to the environment.

Who was ‘Uncle Charlie’?
       1809-1882.
    Born in Shrewsbury, England, ON THE SAME DAY AS WHO?  Feb. 12, 1809.
    Darwin was a confused premed.
    Went to Med School at Edinburgh, but switched to theology at Cambridge,
      got his degree, then needed a rest.
    Had intentions of being a country parson.
    Captain of the Beagle needed a ‘ship’s companion’.
        Darwin wanted to go.
        Got permission from his father, after intervention by a prominent professor.
         Left in 1831.
        Beforehand, was tutored in botany, zoology, specimen preparation, geology etc.
    
   Darwin was an Anglican and a creationist when he boarded the Beagle.
     
He collected numerous speciments of plants and animals (e.g. birds) and sent them back to England.
   Like any good scientist, he kept thorough journals.
Darwin had an opportunity to see variation in species that can be found in a range of environments.
Compared plants, animals in S. America with those of the Galapagos Islands.
   (For a great book on the Galapagos, read 'EVOLUTION'S WORKSHOP', by UGA historian, Edward Larson.
      Also, SUMMER FOR THE GODS by Larson. THE definitive account of the Scopes trial)
Darwin wondered why plants and animals on each island were similar to those on the mainland, yet unique in some ways.
Patterns in variation suggested that organisms on the islands were somehow derived from organisms on the mainland.
He surmised that rare dispersal events brought species from mainland to the islands, where they slowly became adapted to local 
   conditions, forming unique species.

After 5 yrs, he returned to England, in 1836.
Spent the rest of his life in relative comfort, but suffered from various maladies
Organized his thoughts, studied all sorts of things (barnacles, orchids, earthworms,
  plant responses to light, facial expressions in people, domestication of animals)
    Darwin was truly a curious person, and a ‘scientist’s scientist’.

Darwin was very much influenced by an essay by Thomas Malthus in 1798 which outlined the 'struggle for existence,'
       pointing out that human populations were expanding more rapidly than the food supply. 
Darwin extrapolated the idea to elephant populations, calculating that without limitation, from just onebreeding pair, 19,000,000     elephants could be produced in 750 years.  
    However, elephant populations remain relatively stable.     
Darwin concluded that variation in a population enabled some individuals to survive longer and produce more offspring than others. 
   Environment breaks population growth.

Darwin recognized that variation is the raw material for evolution.
    Studied domestication of animals and plants. How breeders select for chance variation.
Also important in his thinking: TIME!!! Lots of it!
    The geological work of Charles Lyell and John Hutton was important to the development of Darwin's theory,
        because it offered the first evidence from that the earth was in fact millions of years old or  more,
          much older than previously thought, and that  sedimentary rocks had been deposited gradually, uplifted etc.  
These findings suggested that enough time had passed for evolution to produce the diversity of species that are present today.

Darwin was content to take his time, until Alfred Wallace came up with idea of evolution independently,
   and sent Darwin his paper to read. Uncle C. was mortified, and his friends immediately arranged to have both studies
    read to the Linnaean Society of London.
Darwin published his book, Origin of Species, in 1859, and it was an instantaneous best seller.

Concept of evolution was in the air well before Darwin
    Not the first explanation for why there are so many different species.
     The predominant theory of the time was special creation. 
All creatures created exactly in their present form as told in Genesis.

However, Linnaeas became convinced the mutability of  species.
     Peloria mutant of Linaria vulgaris,
        ‘Butter and Eggs’.
Lamarck's bogus evolutionary hypothesis on inheritence of acquired characteristics preceded Darwin.

Remember: this was also a time of THE ENLIGHTENMENT, when scientists sought rational,
  naturalistic explanations for the natural world.

Lots of questions at the time. E.g.:
    Fossils: What are they?
    Why are seashells found on mountain tops all over the world?
    Why are the animals in Australia so different from  others around the world, but so like each other.
    Why is Australian Flora so distinctive, e.g. Eucalypts?
    Anatomy: why do the bones in a bird wing look like those in a human arm?
    Why do primitive snakes have the remants of hind legs, as do whales?
Why do mammalian embryos look so similar?

AND, Why do we get goose bumps?!!!!!!!!!!  (why do we?)

The Mechanism - Natural Selection  
    Darwin had already figured out that organisms within a species differ, and that not all of them would survive to reproduce. 
       How then, were the 'successful' ones 'chosen'?
Darwin took cues from artificial selection of animals and plants.
Darwin saw that only allowing individuals with certain 'desirable' characteristics to breed, led to changes in the average appearance of 
   the population.
 
In nature, selective agents differ (they're not people but the environment), but the process works the same way.
        E.g. plants that grow on mine tailings or other toxic soils are resistant to heavy metal poisons.

Things to recall:
Genetic information resides in the chromosomes as genes.  (Darwin didn’t know about genes).
Every multicellular organism has two sets of chromosomes, and therefore two sets of genes.
   Each set constitutes one genome.
We inherit one half of its genetic information from one  parent, and half from the other.
Genes come in different ‘flavors’, or versions, called  alleles.
Gene pool - set of all versions, or alleles, in all genes, for all the individuals in a population

Natural Selection - non-random selection of  ‘genotypes’ due to environment.
    Ecotypes - genetic change in response to local  environmental conditions.
    Evolutionary arms race - evolution of defenses against that which would eat you.

Different types of selection pressures. E.g., sexual selection, selection by predators.
   Remember guppies!!!!!??????

A SPECIES: group of organisms capable of breeding and  producing viable offspring.
Problem: this is a ‘soft’ definition. Scientists don’t fully agree on the definition as it applies to all organisms.
  Also, plants differ from animals. HOW!!!!!!!??????

It’s necessary to achieve reproductive isolation in order for species to form.
Allopatric speciation
    Result of geographic isolation
      Formation of natural barrier. e.g. islands, mesas, etc.
Sympatric speciation
      No geographical isolation.
      E.g. insect host switching. Apple/Hawthorne/fruit fly.
       Polyploidy in plants - increase in number of chromosomes. Stabilizes hybrids
        (usually doubling of chromosomes)

Scientists believe speciation in plants was mainly accomplished by hybridization and polyploidization

Modern molecular biology reinforces and extends ideas about evolution.
    The nature of mutations.  E.g. Mendel’s characters.
    Gene sequences house historical information.
    Phylogenies based on gene sequences largely agree with other schemes.
    Why so many odd and seemingly useless DNA in our genomes?
       E.g. transposable elements, dead viruses, etc.
        Can only be explained by evolution.
    Why did some of these sequences appear in certain groups around the time they arose and diversified?
      e.g. primates, humans, grasses?
    Where did HIV come from? Only evolution offers explanations.
      Also, why different versions of flu (now, boid flu or avian influenza) every few years?