Lecture week 1 (8-24) - Notes Introduction to Evolution

What did we know before the mid 1800’s?

• organisms have offspring similar to themselves

• we could select individual plants and animals on our farms to breed and produce offspring that we considered beneficial

• there exists a large amount of diversity/variation among organisms within a species

• differences among the members of a population mean that not all are affected in the same way by ecological factors

• the variation between species may mean that not all areas that can do so will support a population of a particular species or actually have a population present

• typically, individuals produce more offspring than what the environment can sustain/support

What did we believe before the mid 1800’s?

• all organisms were created by a divine being, Special Creation, as recently as 6000 years ago

• species have never changed and are unchangeable

• Aristotle’s Great Chain of Being: all species are organized into a sequence based on increased size and complexity, with humans being at the top

• variation between individuals is unimportant or misleading

Jean-Baptiste de Lamarck

• first to state that species have changed through time - 1st formal evolutionary theory

• species change through time via acquired characteristics, that is, individuals change as a result of environmental pressures and then pass those traits to their offspring.

• acquires characteristics are not normally passed from one generation to another

What were Darwin’s conclusions based on the Origin of Species (book)?

• variation, in conjunction with environmental pressure, is the key to understanding diversity and how and why species change

• Natural selection had 3 components

What are the three components of natural selection based on Darwin’s theory on the Origin of Species?

• all species have a common ancestor

• all species show change in characteristics through time

• all species show changes in characteristics in different environments

Components of the Modern Theory of Natural Selection?

• evolution

• natural selection

• adaptations

Evolution

the change in genetic (allelic) frequency within a population over time

Natural Selection

a process by which evolution occurs

What does Natural Selection require?

• Trait variation in a population: without variation there are no traits to select for and against.

• Heritability: the traits in question (variation) need to be heritable.

• Differential survival: describes how animals, plants, and other living organisms manage to successfully survive changes to their environment or fail and die out

• Differential reproduction: a process of favoring survival and reproduction of the fittest individuals in a population

Greater survival and reproduction leads to?

being naturally selected for

• selected to survive in nature because of the traits they posses.

Fitness

the number of viable offspring you produce in your lifetime

Adaptations

traits that are selected for

• a heritable trait that increases the relative fitness of individuals having the trait

• a process by which individuals within a population acquire traits that increase their relative fitness.

Artificial Selection

the selecting agents, that which drives the evolutionary processes, are humans

• ex. dog breeding. It doesn’t occur without the help of humans and they do so in order to get the desirable trait passed to their offspring.

Macroevolution

the change of one major taxonomic group into another, or the creation, or extinction of species

The 1st and 2nd conclusions of the evolutionary theory

1. specie are related

2. species and species diversity change over time

Microevolution

the change in a population over generations that helps to separate populations from each other genetically

• the accumulation of microevolution over a long period may result in the creation of new species (macroevolution)

• the 3rd conclusion of the evolutionary theory

evidence that some species are related.

• geographic proximity of similar, non-interbreeding species

  • extreme similarity and close proximity suggest relatedness

• homology: similar traits in separate species due to a share common ancestor

evidence that species and species diversity change over time.

• fossil record:

  • not all species were together at one time

  • extinction has taken place

  • transitional forms exist

  • major increases in species complexity takes billion of years

  • life began in the sea

• vestigial traits: structures in organisms commonly found in the species that serve little or no function

Types of homology

• Genetic Homology: similar gene sequences between individuals of different species

• Developmental Homology: similarities in morphology of embryos of different species

• Structural Homology: similarities in structure of body parts of different species.

Atavism

a vestigial trait found in very few individuals within a species

misconceptions about evolution

• if evolution is true, there is no God

• humans evolved from apes

• individuals evolve

• adaptation occurs because a species needs/wants it

• evolution always result in a more complex or better organism

• all traits are adaptive

• functional traits have unlimited adaptive potential

Evolutionary trends

• an increase in mutlicelllularity

• an increase in complexity

• an increase in ways to capture energy for use

• an increase in ways to deal with the environment -biotic and abiotic

• an increase in diversity