Day 41 Speciation and the History of Life
Speciation
How does one species become two?
In order for speciation to happen there has to be some type of reproductive isolation
-The definition of a species is a group or populations whose members have the potential to interbreed in nature and produce viable, fertile offspring- but do not produce viable, fertile offspring with members of other such groups
-Because the definition has to do with mating a population needs to be kept reproductively isolated from another until they have changed so much that they can no longer breed
-There are two types of reproductive isolation
-Prezygotic barriers - Before sex
-Postzygotic barriers- after sex
Now lets label them
Allopatric and sympatric speciation
Allopatric speciation is when one species becomes two while being geographically isolated
Sympatric speciation is when one species becomes two while still living in the same geographical region
Sometimes Hybrid zones are created
A hybrid zone can go through 0ne of three phases
-Reinforcement
-Fusion
-Stability
A mutation can lead to instant speciation in Polyploidy
-Polyploidy is when you have more than two of every chromosome (Diploid)
-If a mutation happens in the fertilization process and a plant becomes Triploid or more it can no longer breed with plants of the same species because the chromosomes do not match.
-But since plants can self-fertilize the polyploid plant can continue to reproduce creating its own species
Adaptive radiation is when many species arise all at once
Extinction
-99.9% of all species that have lived on this planet are now extinct
-The number one cause of extinction is environmental change
-Some things that make species vulnerable to extinction
-Localized distribution
-If the entire species lives in a small area then if something happens to that area the entire species can go extinct
-If a species lives all over the world than it is less likely that a catastrophe will kill off all of their populations
-Overspecialization
-If an animal only eats one type of food then they are more vulnerable to extinction
-If that food is depleted then they will all die
-By having a large range of diet there can be other alternatives if one food source is gone
There have been 5 mass extinctions on this planet and humans might be the cause of the sixth
The History of Life
(Some of this information is hypotheses based on strong scientific evidence but cannot be proven due to the fact that it happened a very long time ago and cannot be repeated)
Before the 1600's it was thought that spontaneous generation was possible
-Spontaneous generation is when an organism can just appear out of nowhere
-This was disproved in 1668 with an experiment with meat and maggots
So the first cell hypothesis goes like this...
The first living cells on earth were here around 3.8 billion years ago
-The earth was very different 3.8 billion years ago
-The earth had very little oxygen on it
-The earth was full of methane, ammonia, hydrogen, and water vapor
-There was a lot of electricity in the air, lots of lava, and volcanoes
-The earth was very hot
-In these early earth conditions it could be possible for the macromolecules necessary for cells to be created.
-In lab conditions that simulate early earth atmosphere amino acids were created
-So the hypothesis is that under early earth conditions there were pools of organic molecules
-These organic molecules were surrounded by drops of oil creating the first protocells
-Once the protocells could self replicate using RNA they were considered living
-The first cells were prokaryotes
-These prokaryotes floated around, some preditory eating other prokaryotes
-Others were photosynthetic like the Cyanobacteria we have today
-The first Eukaryotic cell came about through a process known as endosymbiosis
-If you remember mitochondria and chloroplast have their own DNA
-This is evidence for the endosymbiosis hypothesis
-Now the earth has both prokaryotes and eukaryotes
-Colonies of eukaryotes became the first multicellular plants and animals
Organism complexity continued to expand into all the groups that we see today
