Chapter 22 Darwinian Evolution

What is evolution ? Descent with Modification evolutionary change is based on the interactions between populations & their environment which results in adaptations (inherited characteristics) to increase fitness Evolution change over time in the genetic composition of a population.

Historical Context of Evolution Darwin was influenced by many scientists in developing his theory.

Aristotle 384-322 B.C Species are fixed (unchanging) Life-forms arranged of scale (ladder) of increasing complexity (scala naturae) Each life form had its permanent place on the ladder Follows Old Testament (creationism) Aristotle 384-322 B.C

Classified diversity for the Founder of taxonomy/binomial nomenclature Domain – Kingdom – Phylum – Class – Order – Family - Genus – Species Domains: Eubacteria, Archaea, Eukarya Nested system: species grouped into increasingly general categories Classification based on anatomy & morphology Grouped species by resemblances from pattern of their creation not evolutionary relationships Carolus Linnaeus 1707-1778 Classified diversity for the “greater glory of God”

Paleontologist – studied fossils Deeper strata (layers) - very different fossils from current life Extinctions were common occurrences yet opposed idea of evolution Catastrophism : events destroyed many living species in local areas, then area was repopulated by immigrant species George Cuvier (1769-1832)

Geology Charles Lyell 1797-1875 James Hutton 1726-1797 Gradualism Uniformitarianismmechanisms of change are slow and constant over time. Slow & subtle changes in organisms lead to big change James Hutton 1726-1797 Gradualism: geologic change results from slow, gradual, continuous process still operating today.

Jean Lamarck (1744-1829) 1801 1. Theory of desire - organisms change due to inborn desire to change to become more fit for environment ex: ant eaters develop long snouts 2. Theory of use and disuse - organs that are being used get large and strong - organs that are not used shrink and eventually disappear ex: snakes- didn’t use legs so disappeared 3. Theory of inheritance - acquired traits were passed on to offspring ex: snakes that lost legs passed trait Importance: Recognized that species evolve, although explanation was flawed

Malthusian Doctrine More babies born than deaths Consequences of overproducing within environment: war, famine, disease Struggle for existence Thomas Malthus (1766-1834)

Charles Darwin (1809-1882)

British naturalist Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas

Unique species

Darwin’s Finches Beak variation: an example of adaptive radiation. 14 species of finches: evolved from one common ancestor in South America

Darwin’s conclusions small populations of original South American finches reached islands variation in beaks enabled some to obtain food successfully in the different environments over many generations, the populations of finches changed anatomically & behaviorally accumulation of advantageous traits emergence of different species

Finches with beak differences that allowed them to… - successfully compete - successfully feed - successfully reproduce

Other examples of adaptations to food source

1859: Origin of the Species Darwin waited 30 years before he published his ideas on evolution Alfred Russell Wallace – published paper on natural selection first (1858) Charles Darwin (1859): On the Origin of Species by Means of Natural Selection Mechanism for evolution is Natural Selection Darwin didn’t use “evolution”, but rather “descent with modification”

Origin of the Species Darwin amassed evidence that descent with modification by natural selection explains three broad observations about nature: The unity of life: organisms share many characteristics The diversity of life: organisms accumulate adaptations The match between organisms and their environments

Darwin’s Theory of Natural Selection Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those without traits.

- organisms produce more offspring than can survive Parts of Theory 1. Overproduction - organisms produce more offspring than can survive - leads to competition

2. Genetic variation - individuals in a given species vary by chance (due to gene recombination) - normal . exception: identical twins

3. Struggle to survive - all organisms face constant struggle to survive (limited resources)

4. Survival of the fittest - Individuals best adapted to environment are more likely to survive and reproduce - Over time favorable traits increase in population Adaptations enhance an organism’s ability to survive and reproduce. Over long periods of time, steady input of new variations in a population lead to speciation.

DIFFERENCE IN THEORIES Lamarck: organisms change in order to survive in environment - occurs in the organism’s lifetime Darwin: environment determines which organisms survive through natural selection - occurs over many generations

Evidences of Evolution Direct Observations 2. Fossil record 3. Homology homologous & vestigial structures embryology molecular: protein & DNA sequence 4. Biogeograpy

1. Direct Observations Antibiotic Resistance: MRSA (methicillin-resistant Staphylococcus aureus)

Soapberry bug beak length shortened in response to change in food source.

2. Fossil record Most occur in layers of rock, with the youngest usually on top, and the oldest in deeper layers (sedimentary rock) Some found in amber (fossilized tree sap) Record incomplete due to soft outer coverings on organisms not leaving imprints 99% of all species that lived on Earth are now extinct.  

Transitional Species (links to modern species) Tiktaalik roseae, a 375 million-year-old transitional species between fish and the first legged animals, reveals that the evolution of hind legs actually began as enhanced hind fins.

3. Homology (similarities among organisms) Homologous structures: structures which developed from a common ancestor, but have changed over time due to different purposes (divergent evolution)

Embryologic similarities evidence of a common ancestor dorsal, hollow nerve cord, notochord (stiffening rod of cartilage) in the back similar membranes in the embryos, yolk sac that produces the first blood cells and germ cells similar development of many organs

Vestigial organs/ structures: Structures which have lost all or most of their original function in a species through evolution. Degenerated, atrophied, or rudimentary condition Evidence of change over time vestiges of pelvic girdle of eyes on nicitating membrane leg bones of walking ancestors blind cave fish

Molecular/ Biochemical homologies DNA, RNA, amino acids, and serology (comparison of blood chemistry) Species Amino Acid Differences from Human Hemoglobin Protein Gorilla 1 Rhesus monkey 8 Mouse 27 Chicken 45 Frog 67 Lamprey 125

Evolutionary Trees Closely related species (branches) share same line of descent until their divergence from a common ancestor Homologous characteristics that are inherited from a common ancestor are strong indications of evolutionary relationships For example, "Tetrapods" all possess four limbs, presumably because they evolved from an ancestor (#2) that had four limbs. Pg 464

Convergent evolution independent evolution of similar features in different lineages Distantly reated species resemble one another Analogous structures: similar in appearance and function, but different origins with different internal structures - organisms with different ancestors become more alike because they share same environment dissimilar structures  more similar structures

4. Biogeography Geographic distribution of a species Species in nearby geographic areas resemble each other - Continental drift and Pangaea explains similarities on different continents - Endemic species: found at a certain geographic location and nowhere else ex: Marine iguanas in the Galapagos

Island Biogeography

Natural Selection vs Artificial Selection Nature selects/decides Man selects/decides Acts on individual Selective breeding Population evolves over time Inbreeding occurs Occurs over long periods of time Occurs in short period of time