Hello marine biology students.
In this final video before Assessment one,
we're going to talk about how, and why, we
organize the diversity of life.
[Intro Music]
So let's start talking about the different
types of marine organisms.
Evolution is defined as a gradual change in
the genetic makeup of a population over time.
Individuals in a population have genetic differences
in their ability to survive, in the form of
finding food, avoiding being eaten, surviving
disease, producing offspring, and many other
attributes.
Natural selection is the process by which
the best adapted individuals are better survivors,
and more of their gametes and more of their
genes will make it into the next generation.
The less adapted individuals may not survive
to reproduce or will reproduce less and thus
pass less of their genes to the next generation,
or I guess I should say, their offspring will
make up a smaller portion of that next generation.
As a result of natural selection the population
continually adapts to its environment, it
evolves.
As a result of natural selection, the gene
pool of a species changes or shifts through
time by changing the frequency of less advantageous
traits in favor of those that are better suited
for survival.
The gene pool changes as a result of pressures
from the environment.
This is what natural selection is.
This is what drives evolution.
Taxonomy is the science of classifying and
naming different species that have resulted
from the process of evolution.
This classification 
is done using different characters and it
can include internal and external body structures,
DNA and protein analysis, and even the particular
places where species live, the habitats they're
found in.
Taxonomy uses several levels of classification,
from the widest being domain and then kingdom
and phylum, to the smallest, which is the
species level.
Species are identified by the use of two names,
the genus followed by the species epithet.
Like Tursiops truncatus is the name of the
bottlenose dolphin.
This two name system is known as the biological
nomenclature.
Now, you may say, “Well, why don't you just
use common names instead?” and the problem
with common names is that they aren't common
everywhere and in fact the same name can refer
to different organisms in different places,
and so, there can be a lot of confusion.
Since science is an international endeavor,
we want to have a naming system that can be
used internationally, by all individuals working
on these organisms.
And so, the Linnaean hierarchy of domain kingdom
phylum class order family genus species and
then identifying a species by its binomial
nomenclature is the system that biology and
marine biology used to describe species.
So here in this chart, we can see the organization
of us as humans or Homo sapiens versus a bottlenose
dolphin, which is Tursiops truncatus.
A species consists of individuals that have
many characteristics in common and the ability
to breed successfully with each other.
This definition is called the biological species
concept, and is one way of defining a species.
When two populations cannot interbreed, they
are reproductively isolated from each other
and therefore they belong to two different
species.
Now, how do you know when there's been enough
change for something to be called a new species?
How much change is required for a new species
to form?
Well, it really all depends on which species
concept is being used.
The biological species concept, which we just
talked about, is based on reproductive ability,
but there are limitations to this definition.
First off, that doesn't work for bacteria
and other microorganisms which primarily reproduce
asexually.
Next, it doesn't work for fossils or extinct
organisms for which reproductive behavior
cannot be assessed or determined.
And lastly, there are many exceptions in biology
and some hybrid organisms can be formed between
two species both in captivity and in nature.
There's a whole field of biology which tries
to determine the relatedness of different
organisms, this is known as phylogenetics.
Phylogenetics 
is the study of evolutionary relationships
or relatedness between different organisms.
Biologists need to use many characteristics
to determine the relatedness of organisms,
such as their structure, their DNA, fossils,
reproductive patterns, embryological and larval
development, habitat, and behavior.
All of these can be used to varying degrees
to determine relatedness of different organisms.
Of all of the fields of biology, phylogentics
sees significant changes relatively frequently.
While this is a source of frustration for
some, these changes come from new understandings
of relationships based on new data and new
information.
The alternative to changing phylogenetic relationships
is to keep them as they were, even though
we have new conflicting information, which
is really not the spirit of science.
For the next several weeks, we're going to
be talking about the diversity of life in
the oceans.
We're going to be discussing prokaryotic domains,
such as domain Bacteria and domain Archaea.
We're going to be talking about several of
the kingdoms within the eukaryotic domain
and really looking at the diversity of life
in the oceans.
That's the end of the videos for this week
we're going to be moving on to discussing
the diversity of life after Assessment one.
All right!
See you in the next video.
