1750 1800 1900

Linn

aeus

Lam

arck

Men

del

Dar

win

Linnaeus (1707-1778)

- Classified and grouped organisms based on their characteristics.

- Developed classification system (ex. humans)- Kingdom (Animalia)

- Phylum (Chordata)- Class (Mammalia)

- Order (Primates)

- Family (Hominidae)

- Genus (Homo)

-Species (sapien)

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Early evolutionist who believed in three principles that drove evolution1) Use and Disuse – Parts of the body that were used developed, and other parts not in use did not develop

2) Inheritance of acquired characteristics – traits that an organism acquired during its lifetime can be passed on3) Species transformation – Acquired characteristics is passed on to the subsequent population

Lamarck (1744-1829)

According to Lamarck, the giraffe’s neck grew longer over time, because of the giraffe’s “desire” to reach the higher leaves. Since they had to use their neck muscles more to stretch and reach the upper leaves, these acquired traits developed and were passed on to the subsequent generations.Back to Timeline

Gregor Mendel (1822-1884)

Augustinian monk, through his study of pea plants helped father the study of modern genetics

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Charles Darwin (1809-1882)

- English naturalist who took a 5-year voyage on the HMS Beagle and studied the diverse species on the Galapagos Islands

- Pubished his book The Origin of Species in 1859, where he discusses his theory of natural selection as the mechanism for evolution

How do Darwin’s evolutionary principles differ from Lamarck’s?

1) Heredity - Natural selection is a process in which some individuals have genetically-based traits that improve survival and reproduction. Genes can be passed on to the next generation.

2. Genetic Variation - There is diversity in any population. Genetic variation in the population can arise due to mutation and the shuffling of genes in meiotic processes.

3. Differential Reproduction: You either have the genes to survive or you don’t. “Desire” has nothing to do with it. If you have genes that help your survival, you will reproduce and leave behind more offspring with your genes than those who don’t.

What is the general way we refer to those who survive?

Fitness:

• An individual’s success at reproducing – (the more offspring the individual leaves, the

higher its fitness).

• Fitness is dependent upon a particular phenotype that individual has.

Evolution of Color in Beetle Populations

1. Genetic variation.For example, some beetles are green and some are brown.

   

 

                              

            

2. Differential reproduction.Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. In this example, green beetles tend to get eaten by birds and survive to reproduce less often than brown beetles do. The green beetles are less “fit”.

    

          

                                                    

3. Heredity.The surviving brown beetles have brown baby beetles because this trait has a genetic basis.

  

  

                           

               

How do we measure evolution?

Measure the allele frequency of genes for both coloration before and after a certain period of time

Overview of the Steps of Natural Selection

1. Organisms have reproductive potential.2. There is genetic variation in a population.3. The genetic variation is heritable.4. Environmental resources are limited and/or there

is a struggle for survival.5. Individuals will compete to survive, so there is

differential reproduction.6. The most fit will pass on its genes to the

subsequent generation, increasing its gene frequency in the population.

7. Evolution is measured and is evident when allele frequencies of genes change over time in a population.

What are sources of genetic variation?

1) Mutations - those created in gametes can be passed on to the next generation (not those in somatic cells)

2) Sexual Reproduction – creates individuals with new, random allelic combinations

3) Diploidy – presence of two copies of each chromosome in a cell

4) Polymorphism - (dominant/recessive interactions, etc. in diploid organisms)

5) Quantitative characters – added effect of 2 or more genes on phenotype (ex. height)

6) Neutral Variation – natural variations that do not offer any selective advantage (ex. Fingerprints)

Misconceptions about Natural Selection

• It is not “Survival of the Fittest;” really it is “Survival of the ‘fit enough’”

   

  

          

                    

  

          

                    

If A = normal blood and a = sickle cell blood, then . . .

AA = normal

Aa = normal

aa = sickle cell

Recessive alleles for disease can stay unnoticed in a population

• Sometimes heterozygotes are more “fit” than homozygotes…

• For ex. sickle cell carriers (Aa) are also resistant to malaria

• This is called heterozygote advantage

Misconceptions about Natural Selection

• Sometimes fitness is dependent upon population frequency

• Ex. Minority advantage– when rare phenotypes have an advantage

over the more common phenotypes– As rare phenotypes increase in population,

they lose their advantage– Often seen in predator-prey situations

Misconceptions about Natural Selection

What evidence do we have of evolution?

1. Homologous Structures – Similarities in physiology due to common ancestry in differing species

What evidence do we have of evolution?

2. Vestigial Structures – Structure of marginal importance to an organism that may have served a more important function in its ancestors… ex. leg bones of a snake

What evidence do we have of evolution?

3. Embryological Homologies – similarities found in the embryonic development of related species

What evidence do we have of evolution?

4. Molecular Homologies – similarities found at the molecular level of related species…ex. DNA, RNA, AA

What evidence do we have of evolution?

5. Fossil Record – reveal pre-historic existence of past species as well as those related species still in existence

What evidence do we have of evolution?

6. Biogeography – the geographic distribution of species

ex. evolution of “endemic” species on islands that are found nowhere else in the world

Blue-footed boobie from Galapagos Islands

What current examples do we have of evolution?

1. Insecticide Resistance

- Application of insecticides kill insects w/o resistance, but promotes the reproduction of those with resistance

What current examples do we have of evolution?

2. Drug resistant HIV- 3TC HIV drug works by mimicking the nitrogenous base Cytosine- within 4 weeks, HIV resistant strains appeared, with the ability to distinguish between 3TC and Cytosine