In part 1 we introduced two major concepts related with idea of Evolution.
That being, the Ladder of Complexity, and the Tree of Life.
Part 2 was dedicated to a timeline to arrive at the modern synthetic theory of Evolution, from Aristoteles to Mendel.
This is part 3, and we'll get into more detail concidering some of the the Driving Forces of #Evolution.
As previously stated in part 2,
thanks to the insight into genetics provided by works of Gregor #Mendel,
and works of science for the next 100 years,
we have formed the modern version of the Theory of Evolution,
far superior to the one proposed by Charles #Darwin,
which was primarely focusing on Natural Selection and Sexual Selection.
Fast forward to today,
confirmed driving forces of evolutionary change and new species emerging are:
- Mutation, viral transmission, and genome rearrangemnets
- Genetic drift, including Founder Effect, and Bottleneck Effect
- Natural selection, and Red Queen Effect
- Sexual selection
- Gene flow, and Isolation
There's also a very strong hipothesis that #Epigenetics could be included in the line-up above.
But that's a topic for another day.
Firstly let's address mechanisms proposed by Charles Darwin himself.
Since they are the most famous ones,
maybe it's a good starting point.
To understand the net of relationships between these processess,
one need to understand the idea of natural selection.
- Mutation, viral transmission, and genome rearrangemnets
- Genetic drift, including Founder Effect, and Bottleneck Effect
Natural selection, and Red Queen Effect- Sexual selection
- Gene flow, and Isolation
Darwin discovered Natural Selection during his sea voyage
on board of the ship HMS Beagle,
travelling around the world starting at Plymouth in England.
One of the stops before diving into Pacific Ocean were Galapagos Islands,
famously home to many different species of Finches,
birds Darwin studied there, along with many other species.
What drew Darwins attention was a great diversity in said birds depending
on the types of food sources available to them on specific island.
The most prominently diverse feature exhibited by the Finches is their beak.
The size and shape of the beak varies significantly across species discovered by Darwin.
It wasn't untill years later that Darwin came to his conclusions.
Darwins assumption was,
that the birds who had slightly bigger beaks would be able to feast on harder foods,
therefore getting more options than their small beak counterparts.
On an island where available food required more beak strenght,
birds with a slightly bigger beak did marginally better.
Hence those individuals, and ones in their offspring which inherited the feature,
had better chances of survival.
That is a basic principle of Natural Selection.
In other words.
If an individual exhibits a trait beneficial to survival,
and their offspring inherits that trait,
sooner or later,
that trait may become dominant in the population that individual belong to.
Just like with the music from the 70'.
Imagine you travel back in time.
If you were in the 70',
you would hear all kind of songs.
Some better,
other terrible.
Fast forward to present day,
most people listen to,
and remember only Hit songs.
But there were countless other songs that have been forgotten nearly 50 years later,
or even a year later.
Generation to generation,
only Hit songs influence people.
That's Natural Selection.
A frequency of feature exhibition in a specie change due to natural selection,
and so,
species change their appearance untill they no longer look like their ancestors.
It's important to realize,
that the evolution of a single specie is as much shaped by other species,
and environment,
as other species are shaped by that single specie evolution.
What does it mean?
It's called the Red Queen effect.
- Mutation, viral transmission, and genome rearrangemnets
- Genetic drift, including Founder Effect, and Bottleneck Effect
Natural selection, andRed Queen Effect- Sexual selection
- Gene flow, and Isolation
In Lewis Carroll's famous book, Through the Looking-Glass, the Red Queen said to Alice
Now, here, you see, it takes all the running you can do, to keep in the same place.
Red Queen effect, or Red Queen hypothesis.
Is an attempt to explain the Law of Extinction,
and the net of interactions between ever-changing environment and species.
Selection of a trait in one specie,
due to selective pressure,
may cause selective pressure for traits in another specie.
According to Red Queen hypothesis,
if one specie gains too much edge over another specie in the evolutionary race,
the later specie may be a subject to extinction.
Little surprise to learn,
based on geological and fossil record,
most species to even exist did in fact go extinct.
If a finch develops stronger beak to eat seeds of a certain flora specie,
only very tough seeds will ever survive to grow into adult plants.
The evolutionary progression of finches
becomes a selective pressure for that tree, or herb to develop harder to crush seeds.
Never ending feedback loop.
Another mechanism proposed by Darwin was Sexual Selection.
Although from a technical standpoint,
Sexual Selection is a form of Natural Selection.
It is important to extract it and discuss as it's very own entity.
- Mutation, viral transmission, and genome rearrangemnets
- Genetic drift, including Founder Effect, and Bottleneck Effect
Natural selection, andRed Queen EffectSexual selection- Gene flow, and Isolation
Like mentioned before,
sexual selection is a special case of natural selection.
In case of this kind of mechanism,
the selective pressure populations are subject to are not external.
Not external in the sense that they don't depend on the environment [only to an extend], nor another species.
Selective pressure is internal,
coming from within the group an individual is a part of.
If there's sexual selection component to one specie evolution,
most of the time it is female making decisions which suitor to mate with.
But it is not a rule.
Take example of slugs.
Slugs are hermaphrodites, or bisexual, [yes, bisexual, look it up]
which means they are both male and female reproductive organs.
Some species for slugs would fight over which one of them will act as male and which as female.
Interestingly enough, sexual selection don't necessarily promote the spread of features beneficial to survival.
Depending on mating rituals and partner preferences,
sometimes traits being empowered outright decrease mobility hence decreasing survival chances.
Take Peacocks
Image Source
A prominent tail like that seems to get in the way more than anything.
It's surprising male peacocks are still capable of flying.
However, females would choose exclusively mates with biggest,
longest,
widest tails they can find.
Worthy of note is the fact, that just because a trait selected through sexual selection may seem to be useless,
don't mean that it in fact is just an irrational behavior on females part to select it.
Often times, it is an indicator of individuals vitality, resistance to parasites and illness.
A sickly peacock would have a hard time growing a really beautyful tail.
- Mutation, viral transmission, and genome rearrangemnets
- Genetic drift, including Founder Effect, and Bottleneck Effect
Natural selection, andRed Queen EffectSexual selection- Gene flow, and Isolation
To be continued...
This post is just one in a serie called Lil' #Science #Dictionary.
The purpose of the serie is educational in nature,
created to explain in simple terms certain scientific concepts.
If you like what you've read, and you want to see more come your way.
Make sure to Comment, Follow, Like, and/or Resteem.
Help Extend the Dictionary by suggesting topics you'd like to see explored.