Biodiversity Set 3 - DARWINS POSTULATES AND NATURAL SELECTION

While Darwin spent % years on the HMS Beagle he…

He visited four continents and many islands, collecting animals, plants, fossils

• He kept DETAILED notes on the behaviors and observations of all topics he studied

Whose Principles of Geology made Darwin realize the earth was much older than he thought

Lyell’s Principles, this in turn supported Darwins discoveries as it gives more time for change to occur → more chances for natural selection to occur

Why did Darwin make note of how fossils were often similar to living species?

He recognized the potential for shared or common ancestry based upon shared traits.

Whilst on a given island Darwin noticed individuals of the same species displayed trait variation (THEY WERE NOT IDENTITCAL) Why is this important for survival?

• Species variation would be important for dealing w/ environmental variation

Some examples of this environmental variation would be food, seeds, and branches these species perched on.

After a lot of thought, Darwin came up with the…

FOUR POSTULATES (an argument or idea) of how natural selection might work

• Developed the MECHANISM, which means it is testable

What is Darwins First Postulate?

Postulate - Individuals within populations are variable in characteristics/traits

(Individual trait variation)

What is Darwins Second Postulate?

Postulate - Some of an individual’s variation is passed on to their offspring. (Variation is heritable)

What is Darwins Third Postulate?

Postulate - In every generation, survival and reproductive success are highly variable (Struggle for survival/existence)

What is Darwins Fourth Postulate?

Postulate - Offspring that survive inherited variation that gave them a survival advantage, and ULTIMATLEY, reproduction. Thus, survival and reproduction are NONRANDOM

What biological sequence encodes traits? What is it called?

DNA sequences of base pairs encode traits. These DNA sequences are called GENES

Trait expressions can be…

they can be determined by one or many genes

What is the proper term for individual genes with different forms?

The proper term is ALLELES -

• The combination of these alleles that determine the particular expression of a trait

A genotype is…

The specific allele that coded this trait (Aa, AA, aa)

A phenotype is…

The expression of said trait in an individual (Blue eyes, Brown eyes, Green eyes)

What are selective pressures?

It is predation, food availability, changes in environment/climate.

Selective Pressures result in…

It results in DIFFRENCES in FITNESS (reproductive output) based upon alleles the individuals possess (variation)

How would you test for natural selection in a natural system?

• Document variable trait variation - phenotypes both external and internal

• Variation HAS TO be present for natural selection to occur and effect the rate of the population

What is the only mechanism of evolution where populations respond/adapt to selective pressure?

This mechanism is natural selection

Is Natural Selection a random process?

NO - Individual organisms are selected for/against based upon traits. Said traits drive survival and reproduction. Which means it cannot be random

Is Natural Selection goal oriented? (Generating traits simply because an organism needs it)

NO - It can only act on existing variation within a population. Meaning it cannot produce new traits for that purpose)

In Natural Selection, does it evolve the individual? (Changes their traits or alleles)

NO - The individual does not evolve, but rather the POPULATION EVOLVES

• Proportion of individuals in a population w/ particular traits/allele can change due to Natural Selection

What is the definition of EVOLUTION

It is the change in frequency of different alleles (traits) for a particular trait in a population over time