EvolutionEvolution

AP BiologyUnit 4

History of Evolutionary Theory

• Linnaeus– Developed a system of

classification based on body structures (morphology)

• Lamarck– Said species could “will”

themselves to change

Images taken without permission from http://65.107.211.206/victorian/science/lamarck.jpg and http://www.necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpg

History of Evolutionary Theory

• Darwin– Natural Selection causes species

to change

• Mendel– Genetics – now used as another

way to look at evolution

Img Src: http://www.panspermia.org/darwin.jpg

5 parts:1. Population growth has the

ability to be exponential.2. Populations tend to be stable

in size (despite #1).3. Resources are limited.4. Individuals vary in phenotype.5. Much phenotypic variation is

heritable.

Natural Selection

Img Src: http://www.abc.net.au/nature/parer/img/galapagos.gif

Natural Selection (in summary)

• There are more individuals produced than the environment can support leads to competition for resources.

• Individuals with advantageous traits in this competition will survive to reproduce and pass on those advantageous traits to the next generation.

 

Artificial Selection• Breeding animals or plants to have the

desired traits

• Ex. Dog & Cat breeds

Great Dane Shar-PeiAmerican curl cat

Images taken without permission from http://www.caine.de.rasa.ham.8m.com/images/shar_pei.jpg, http://www.petsmart.com/aspca/images/dogs/great_dane.jpg, http://www.cfainc.org/breeds/profiles/articles/acurl.html

,

Newer developments in Artificial Selection

• Cocker spaniel + poodle = Cockapoo

• Labrador + Poodle = Labradoodle

• Why mix with poodles?– Their fur tends to shed

less– they were originally bred in an effort to create a guide dog for people who were allergic to dogs.

Vestigial Structures

• Structures that are no longer used in an organism– Ex. Appendix, tail

bone

• Many structures present in embryos are also used to show common ancestry -- developmental biology

Img Src: http://www.vh.org/adult/provider/anatomy/AnatomicVariants/SkeletalSystem/Images/19.html

A fictional vestigial structure

Analogous Structures

– Similar functions, different structures

– Indicates different ancestors

– Ex. Bird wing, butterfly wing

– Result from convergent evolution: similar selection pressures cause similar structures to evolve.

Homologous structures

– Similar structure, different functions

– Indicate a common ancestor

– Ex. Human hand, seal flipper, bat wing

Biogeography• Study of distribution of

organisms (past and present) • Demonstrate that organisms can

evolve similarly to one another in similar environments from different ancestors

• Ex. Marsupials in Australia – they are only found in Australia but some share similar characteristics with other organisms

Genetic Drift

• Changes in the gene pool caused by random events

• Examples: Bottleneck Effect, Founder Effect, Geographic Isolation

Bottleneck Effect• drastic reduction in population (due to natural

disasters, predators, etc.)

Img Src: http://www.7blueseas.com/destinations/images/map_southpacific.jpg

Img Src: http://www.genomenewsnetwork.org/articles/06_00/pingelapese_colorblind.shtml

Example of Bottleneck Effect: Pingapalese People

Img Src: http://easyweb.easynet.co.uk/~iany/patterns/images/cheetah.jpg

Img Src: http://www.meerkats.com/images/cheetah-cub.jpg

Example of Bottleneck Effect: Cheetahs

Founder Effect

• A few individuals become isolated from the original population

• The resulting population is not representative of the original population

Example of Founder Effect

Img src: http://www.emedicine.com/ped/images/296682EVC-polydactylya.jpg

Img Src: http://www.emedicine.com/ped/topic660.htm

Another Example of Founder Effect: Ellis-van Creveld Syndrome

Geographic Isolation

• When physical separation/isolation results in the formation of new species

• Is a cause of founder effect

• Adaptive radiation = many species evolving from one original ancestor

Img Src: http://www.desertfishes.org/na/cyprinod/cyprinod/cssalinu/cssalin1.jpg

Example of Geographic Isolation

Gene Flow

  Migration (immigration, emigration)

• Breeding across prior barriers (cultural barriers, for instance, as in human populations)

• Changes allelic frequencies

• Ex. Human migration

Phenotypic Polymorphism

• Defined as variety of physical traits

• Due to

- genetic variation

- genetic polymorphism

- nonheritable variation

Fitness

  fitness = contribution of individual to gene pool, relative to others’ contributions

  relative fitness = contribution of a genotype (all individuals alike)

  fitness of 1 means you (or your genotype) contribute at a maximum (100%)

• fitness of 0 means you (or your genotype) do not reproduce at all

Types of Selection

• Selection = Environment chooses those with the best adaptations to survive

Stabilizing Selection = middle phenotype is selected for

Disruptive Selection

• The two extremes are selected for

• Ex. Snails

Img Src: http://web.nmsu.edu/~wboeckle/pepper_moth2.JPG

Directional Selection = one phenotype is selected for

Industrial melanism

Heterozygote Advantage

• When being heterozygous gives you an advantage

• Explains why a harmful recessive allele does not get eliminated from a population

• Ex. Sickle cell anemia – heterozygotes are resistant to malaria

Img Src: http://www.unomaha.edu/~swick/images/sickel.jpgImg Src: http://www.nidcd.nih.gov/news/releases/02/malaria.jpg

Sexual Selection

• Genders appear different due to Sexual Dimorphism

• Competition is inter- and intragender specific

• Ultimately has to do with competition for higher fitness

Constraints on Natural Selection

• Populations are not perfectly suited to their environments because– Environments constantly change and offer new

challenges– individuals present might not have been the ones who would be best suited (Ex. A new population of people marooned from a breaking ship begin a new population. They do not necessarily represent the best of the gene pool)

Constraints on Natural Selection

• Populations are not perfectly suited to their environments because– Evolution is slow and dramatic new structures

rarely form/appear; instead, old structures are used for new structures (Ex. Birds have 2 wings rather than 4, which could help with flight, because they evolved from a 4-appendage reptile; 2 wings and 2 legs)

Constraints on Natural Selection

• Populations are not perfectly suited to their environments because – Adaptations are often compromised (Ex. seal

legs would help in land motion, but swimming with legs is less efficient than with flippers)

Constraints on Natural Selection

• Populations are not perfectly suited to their environments because – Natural selection can only pick the best

variation—it can’t create variations