Ch 2

Evolutionary theory - living species can change overtime and give rise to new kinds of species with the result that all organisms ultimately share a common ancestry

Evolution - material evidence of change over time

  • Ex: fossil record

  • Darwin's finches beak sizes differed on galapagos islands vs. Ecuador’s mainland due to food availability 

Pre-Darwinian Views

  • Saw the world as fixed and unchanging

Essentialism - belief in fixed ideas that exist perfectly and unchanging in eternity; actual objects in the temporal world, like cows and horses, are imperfect material realizations of the ideal form that defines their kind

  • Derived from Plato, Greek philosopher 

  • Ex: real cows revealed “cowness” essence from ideal cows

  • “Each species is characterized by its unchanging essence…and separated from all other species by a sharp discontinuity”

Great Chain of Being - Unilateral framework interpreting the world based on Aristotle's principles which claimed every kind of living organism was linked to every other kind in an enormous divinely created chain. an organism differed from the kinds immediately above it and below it on the Chain by the least possible degree. they were ordered based on the degrees to which they depart from the Divine ideal 

  • Humans had a unique ranking, due to their physical bodies and spiritual souls

Taxonomy - classification; in biology, the classification of various kinds of organisms

Genus - different species are grouped together on the basis of similarities

Species - reproductive community of populations that occupy specific niches in nature

Catastrophism - abruptly wiped out and replaced species due to natural disasters, floods etc., replacing species equally as fast

  • Catastrophists believed that new species replaced old one and had been specially created by God

Uniformitarianism - understanding current processes can be used to reconstruct the past history of the earth, based on the assumption that the same gradual processes of erosion and uplift that change the earth’s surface today also worked in the past

  • Argued catastrophists viewpoint: claimed that while God might allow the world to change, a divine blueprint for creation could not include sharp breaks between different forms of life and the abrupt disappearance of species through extinction

  • Charles Lyell argued erosion works the same way today as in the past

Lamarck’s Viewpoint

  • Wanted to preserve the traditional view of a harmonious living world

  • Suggested fossils were forms of ancestors of living forms

    • Explained fossils looked different from descendents because their features were modified overtime 

  • Believed all species had the ability to change physically in response to their environments; capacity to activate this ability whenever environmental changes occurred

Transformational evolution - Lamarckian evolution; assumes essentialist species and a uniform environment; each individual member of a species transforms itself to meet the challenges of a changed environment through the laws of use and disuse and the inheritance of acquired character

  • Ex: Pandas and bamboo. Suppose pandas originally had wrist bones, then their environments changed and they became reliant on eating bamboo, in order to eat, pandas needed to use their wrist bones to strip the bamboo stalk to get to the edible contents, this strenuous activity led to the formation of elongated wrist bones aka thumbs, pandas then birthed offspring with these ‘thumbs’

  • Lamarck believed all individuals of species developed in the same way, leading to identical evolutionary responses

Lamarck’s ideas were eventually rejected once geneticists were able to demonstrate that neither the law of use and disuse nor inheritance of acquired characters applied to genes

Darwin and Wallace discoveries

  • Both concluded there was a common ancestor

Darwin

  • Lyell’s statement that “deep time” existed gave promise to Darwin’s conclusions

Natural Selection - explanation of descent with modification; 1. Every generation, variant individuals are generated within a species because of genetic mutation 2. Those variant individuals are best suited to the current environment survive and reproduce more offspring

  • Disproves essentialism

  • Darwin argued its more important to examine the differences in species rather than their commonalities 

Variational evolution - variant members of species respond differently to environmental challenges; more successful variants are fitter, so they survive and reproduce more offspring who will inherit the traits that made their parents fit

  • Darwin introduced competition for resources

3 principles of Darwinian evolution

  1. Variation; no 2 individuals in a species are identical

  2. Heredity; offspring tend to resemble their parents

  3. Natural selection; different variants leave different numbers of offspring

  • Driving force was “survival of the fittest”

Ex: pandas and bamboo; pandas with long wrist bones birthed children with long wrist bones, pandas with short wrist bones birthed children with short wrist bones (variation and heredity). When climate changed and pandas depended on bamboo, pandas with short wrist bones couldn't eat the bamboo and died (struggle for existence)

Aptation - any useful feature of an organism regardless of origin

Adaptation - useful feature of an organism shaped by natural selection

Exaptation - useful feature of an organism originally shaped by natural selection for one purpose, but later reshaped by different selection pressures to perform a new function

Genetics

Pangenesis - theory of heredity suggesting an organism's physical traits are passed on from one generation to the next in the form of multiple distinct particles given off by all parts of the organism; blending of both parents traits

Mendelian Inheritance - view that heredity was based on non blending, single-particle genetic inheritance

  • Crossed pea plants; traits that did not appear in F1 appeared in F2, if blending was occurring, all offspring would show same color - revealed discrete traits

  • Expressed particles are dominant, discrete particles are recessive

Principle of Segregation - individual gets one gene for each trait from each parent

Principle of Independent Assortment - Mendelian inheritance in which each pair of genes separates independently of every other pair when germ cells are formed

Genetics - coined by Bateson, scientific study of biological heredity

Homozygous - fertilized egg that receives the same particle from both parents for a particular trait

Heterozygous - fertilized egg that receives a different particle from each parent for same trait

Gene - refers to particles 

Alleles - different forms genes can take

Chromosomes - sets of paired bodies in the nucleus of cell made up of DNA and contain hereditary genetic information that organisms pass on to their offspring

Mitosis - the way body cells make copies of themselves; chromosomes in nucleus duplicate and line up along the center of the cell, then cell divides, each daughter cell taking one full set of paired chromosomes

Meiosis - the way sex cells copy themselves; begins like mitosis, however each daughter cell divides again without chromosome duplication, creating only a single set of chromosomes

Locus - portion of the DNA strand responsible for encoding specific parts of an organism's biological makeup

Linkage - inheritance pattern when unrelated phenotypic traits regularly occur together because genes responsible for those co-occurring traits are passed on together on same chromosome

Crossing over - when one part of chromosome breaks off and reattaches itself to a different chromosome during meiosis


Genes and Traits

Discontinuous variation - pattern of phenotypic variation when the phenotype exhibits a sharp break from one member of population to the next

Polygeny - many genes are responsible for producing a phenotypic trait, like skin color

Continuous variation - pattern of variation involving polygeny in which phenotypic traits grade imperceptibly from one member of the population to another without sharp breaks

  • Proves mendelian genetics can be used to explain discontinuous and continuous variation

Pleiotropy - single gene may affect more than one phenotypic trait

  • Ex: allele that causes the feathers of chickens to be white also works to slow down their body growth 

  • Revealed genes do not produce traits in isolation

Mutation - creation of new allele for a gene when the portion of DNA molecule to which it corresponds is suddenly altered

  • Occurs randomly 

  • Proves inaccuracy of Lamarckian evolution which proposes modifiable inheritance

  • It’s impossible for genes to accurately provide the “needs” 

  • Some mutations are harmful, some helpful; helpful ones move on through natural selection

DNA - carries the genetic heritage of an organism as a blueprint for organisms construction and development

  • Instructions for protein synthesis

  • Double helix, twisted ladder rung with bases (A,T,G,C)

  • DNA is copied prior to mitosis or meiosis

    • DNA breaks into two strands, produces two identical copies of same DNA molecule

Genome - sum of total genetic material in a cell nucleus

  • Contains 20,000 genes (humans)

  • Justifies Lamarckian evolution rejection

Norm of Reaction - table or graph which displays the range of phenotypic outcomes for a given genotype in different environments

  • Some genotypes can present multiple phenotypes, based on the environment

  • Ex: human eye color genotype is relatively similar, except phenotypically expressed different 

Niche Construction - when organisms actively perturb the environment in ways that modify the selection pressures experienced by subsequent generations of organisms

  • Organisms interact with their environments, using it for resources like food and protection; all of these things modify (somewhat) the natural selection pressures of their environment 

  • Members least fit for their environments are the individuals that exhibit the strongest evidence of natural selection

Human agency - the way people struggle, often against great odds to exercise some control over their lives

  • Niche construction and human agency introduces feedback into the evolutionary dynamic and modifies selection pressures

  • Humans always have the opportunity to take action but don’t always do so