​Evolution Day 2: Natural Selection Terms and Conditions

What even is Natural Selection

Darwin reasoned that natural selection results in favorable traits being represented more and more and unfavorable ones less and less in ensuing generations of organisms.

These traits can be selected for/against by several factors in the natural environment.

The Factors Doing the Selecting

1. Overproduction: Within a population, more offspring are produced than can survive due to limitations of food and living space

2. Competition: Individuals compete for food, shelter, and opportunities to reproduce!
   Remember Thomas Malthus? #1 and #2 were his whole deal.

3. Variation: Some individuals are better able to survive than others due to natural differences

4. Survival of the Fittest: Individuals better fit to survive are more likely to live long enough to reproduce

The Factors Doing the Selecting

5. Transmission of Favorable Variations: Favorable characteristics that allow for survival and reproduction will be passed on to the next generation. Characteristics that reduce an organisms chance of survival will decrease over time (descent with modification)

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6. Evolution of a New Species: Accumulation of advantageous variations will eventually lead to the evolution of a new species better adapted to the environment.

Panthers are just jaguars/leopards with a condition called Melanism (their body makes a lot of melanin, which makes them a darker color). It's rare to see in nature because it makes them stand out, not favorable.

What causes variations?

Changes in the genes in gametes of sexually reproducing organisms can be passed onto offspring (aka mutations in the DNA of SEX CELLS, like sperm and eggs). Mutations in body cells will NEVER be passed onto offspring. The mutations MUST occur in the DNA of SEX CELLS. There are two ways that an organism can have gene combinations that differ from the parent:

1. Genetic Shuffling
The sorting and recombination of genes during meiosis and fertilization results in new combination of genes
This is the major source of variation is sexually reproducing species. For example, a human couple could produce an estimated 70 trillion genetically unique offspring!
Think about how crossing over and independent assortment (during Meiosis) can make new genetic combinations by mixing maternal and paternal genetic material on each chromatid

What causes variations?

2. Random Mutations
Change in the nucleotide base sequence (ATCG) of a DNA molecule - Mutations are random and unpredictable. They can be due to random error in transcription/translation or caused by a mutagen (UV light, X rays, cigarette smoke, some chemicals).
- Mutations are important sources of new genes
- Mutations in body cells cannot be passed on, but ONLY mutations in sex cells (sperm & egg) can be passed on. Mutations in sex cells are the basis of evolutionary changes
- Most mutations are harmful, but a few can be beneficial and could lead to a new species

Table Talk

On your whiteboards, come up with an answer to the following:

Why must the cause of variations occur in gametes/sex cells to pass onto offspring?

SOME IMPORTANT CONTEXT

Acquired Traits/Characteristics are NOT a source of genetic variation (Sorry Lamark) because they are developed in body (somatic) cells and are not based on genetics.

The environment does NOT induce adaptation.

Individuals BORN with advantageous phenotypes SURVIVE TO REPRODUCE.

Why do we care?

If environmental conditions change, organisms that have become adapted to those conditions may die! Genetic diversity or variations of organisms allows the species to survive. Once diversity is lost it is impossible to get it back