the 5 theories of darwinian evolution

darwinian evolution takes into account

VARIATION

that is why darwinian evolution is sometimes referred to as

variational evolution

pre-darwinian thoughts on evolution, particularly lamarckian,

did not take into account variation

argued that Darwinism should be viewed as five major theories

ernst mayr

the first 3 theories are

accepted as having universal application throughout the world

1. EVOLUTION AS DEFINED, THAT ORGANISMS CHANGE OVER TIME

- the world is neither constant nor perpetually cycling, but is changing, with continuity between past and present forms of life

- evolution is a biological fact

- fossil records are the most importance evidences

- we can see this in morphological and molecular changes

2. COMMON DESCENT WITH MODIFICATION

- all forms of life descend from a common ancestor through a branching of lineages

- also considered to be a biological fact because it is observable.

all species of life now are (2. COMMON DESCENT WITH MODIFICATION)

descendants of species that came before then, and so on, until we get to the theoretical last universal common ancestor (luca) of life

LUCA (2. COMMON DESCENT WITH MODIFICATION)

- chemical abiogenesis

- 4 bya

from here, many branches of life have begun to (2. COMMON DESCENT WITH MODIFICATION)

emerge.

This goes against Lamarck's beliefs, as he stated that

evolution happens at a linear pace.

life's history has

the structure of a branch- ing evolutionary tree, called a phylogeny.

all these speciation events have resulted in a (2. COMMON DESCENT WITH MODIFICATION)

branching network of lineages, thus earning

the term "Tree of Life."

with every split, (2. COMMON DESCENT WITH MODIFICATION)

there are modifications in the genotype

and phenotype

3. GRADUALISM

- large differences in traits that characterize species originate through accumulation of small incremental changes over long periods of time

- evolution is not slow, but incremental

- evolution is an accumulation of small changes

- this can also occur in saltations

gradualism theory is important because

genetic changes that have large effects on organismal form are usually harmful to an organism

although gradual evolution is known to occur,

it may not explain the origins of all structural differences that we observe among species

in most cases, however, (3. GRADUALISM)

evolution occurs gradually

4. POPULATION SELECTION/MULTIPLICATION OF SPECIES

- the evolutionary process produces new species by splitting and transforming older ones

- population is the unit at which evolution takes place

- darwinian evolution is based on variation of traits among organisms in a population

we measure population selection as (4. POPULATION SELECTION)

changes in allele frequencies

we have to see these frequency changes (4. POPULATION SELECTION)

throughout the

population—a certain subset of them. We don't look at

individuals.

it is possible for 1 population of the same species to (4. POPULATION SELECTION)

evolve into a different species whereas the population of that same ancestral species remains as it is.

5. NATURAL SELECTION

- survival based on differences in fitness and phenotypes

first proposition of natural selection

variation among organisms (within populations) for anatomical, behavioral, and physiological traits

second proposition of natural selection

variation is at least partly heritable so that offspring tend to resemble their parents

third proposition of natural selection

organisms with different variant forms are expected to leave different numbers of offspring to future generations.

"survival of the fittest" is

not the best definition as fitness does not refer to how physically strong an organism is, it refers to the ability of an organism to pass their genes to the next generation. Heritability.

for any given environment, with its various pressures on organisms,

certain phenotypes (i.e. traits) have higher fitness (ability to survive and reproduce) than others, meaning that they're more likely to be passed off to the next generation before their bearers die.

Accumulation of such changes leads, over long periods of time, to

production of new organismal characteristics and new species

Natural selection is therefore a creative process that

generates novel forms from the small individual variations that occur among organisms within a population.

adaptions

- traits that confer survival advantages

- core of natural selection