where does biodiversity come from the
simple answer to that question is
evolution and we could leave it at that
we could all go home because we're done
but that's not going to make much of a
video what we really want to ask
ourselves is what is that what is
evolution and how does it result in
biodiversity I like to think of the
study of evolution as following two
fairly simple pathways these paths are
pattern and process both of these are
not only fascinating areas of study but
are crucial in expanding our knowledge
of how life originated and how it
continues to evolve the pattern pathway
studies the shape of evolution itself by
looking at relationships relationships
among organisms over time and to do that
you need to create a diagram or
structure that links these organisms in
time showing a branching sequence of
relationships much like a family tree or
genealogy these evolutionary trees
record not only the relationships among
the organisms but the events that
occurred over time that indicate why we
think these different organisms are
related patterns depicted by
genealogical trees really are subject
all on their own called
phylogenetic systematics but let's set
that aside for a moment the process path
is maybe a slightly better way to start
we want to talk about the mechanisms of
evolution how it actually happens these
are the drivers of the diversity along
the multitude of lineages that spring
out branching and branching up the tree
up the limbs of the Tree of Life
Darwin and even some of his predecessors
understood this they could see that
things could change that the pattern of
life this tree existed that evolution
happened and that the relationships
among organisms could be traced by
looking at features of those organisms
and how they change depending on where
they were in the tree they could see for
example that the wings of birds the
front legs of mammals and
tiles and in fact all the four limbed
animals indicated that there was some
common relationship there there was a
common lineage but at the same time you
could have change among the branches
within those lineages you could get a
change in the front leg to a wing or to
a grasping arm general patterns were
evident in everything but at the time
there wasn't a good understanding of the
mechanisms the processes that could
explain how these obviously changing yet
related forms could come about Darwin
and his contemporaries read a lot of
stuff about variation which was visible
all around them it could all be seen
they realized that not all the
individuals in a species or even in a
population were exact duplicates of each
other this was a surprise to some people
but the evidence was everywhere even in
things as simple as the speed of
racehorses if you didn't have variation
and how fast horses could run the races
would be pretty boring races actually
demonstrate how horses were chosen for
variations in speed humans bred fast
horses with each other to get even
faster horses and these horses were
selected for being the fastest and
that's the keyword selection Darwin
thought hey what if nature worked that
way
what if nature's selected organisms
somehow he noticed that the form in the
physiology and the behavior of plants
and animals varied within natural
populations just as much as they did in
domesticated populations of things like
horses Darwin realized that what we're
really talking about here are the
beginnings of the understanding of the
evolutionary mechanism behind evolution
natural selection natural selection
means that some natural variants some
individuals with different form or
physiology or behavior might be better
at getting through life than others
better that is at gathering food staying
away from predators turning sunlight
into usable energy resisting wind having
good root systems in other words fitting
the circumstances of the environment and
surviving what Darwin was really saying
is that fitness of an individual meant
being better
able to produce offspring that had
traits like the parent traits that would
help the offspring be better suited to
the conditions of their environment this
has been referred to as survival of the
fittest actually I prefer the phrase
survival of the fit because fittest
implies that there's an end point that
there's a goal but there isn't it's all
relative because there are so many
compromises and trade-offs and being
well suited to a place as complex as the
natural world that organisms can never
reach that perfect match in all respects
this process of the environment
selecting variants that are better
suited to that environment no matter how
complex is called natural selection and
those traits that make the selected
variants better able to survive and
reproduce and pass on those trades to
future generations are known as
adaptations for example a wild
population of redwood trees might have
some individuals that attained greater
heights than others and this results in
better exposure to sunlight on foggy
days enhancing their ability to make
food by photosynthesis when a change in
the environment such as the fog rolling
in challenges the survival of shorter
trees this in turn not only increases
their individual chances for survival
but it also makes available more energy
to the taller redwoods to produce more
seeds that carry this tallness trait
into future generations so you get
natural selection for at ulna Strait and
an adaptation to an environment that can
present changes of course as I mentioned
these simplistic examples kind of skim
over the fact that there's always a
series of trade-offs in nature we have
to consider for example that taller
trees might have more trouble getting
moisture from the roots all the way up
to the tips of those highest branches or
that they could be more exposed to
storms that could knock them down or
maybe there's some other physiological
cause that we might not even have
thought of all these factors are part of
a complicated balance that optimizes
life to a given environmental situation
or set of competing selective factors
stuff happens life is never simple to me
all these aspects come
together to represent the great beauties
of life this constant interplay of
processes that results in the complexity
of biodiversity what Darwin called
grandeur in this view of life the
flipside of the selection coin is that
individuals in a population can also be
selected against because they're less
well adapted sometimes because of
susceptibility to diseases or simply by
not being good at avoiding being eaten
something that keeps those individuals
from being reproductively successful you
might have noticed by now that there's
an important element to the story of
variation selection and adaptation
that's missing here Darwin noticed it
too he was a very smart guy and he fully
recognized that there had to be some way
by which organisms could pass on those
selected traits those adaptations to
their offspring
it wouldn't work otherwise there had to
be a way that the offspring of
individuals that had been selected for
could inherit the traits of their
successful parents and ancestors in
Darwin's day there wasn't a good
understanding of a mechanism for that it
was only much later that scientists
discovered how information is stored in
genetic material and passed on to
offspring
today our detailed understanding of
evolutionary processes is built on the
discoveries of both Darwin and
geneticists stepping back now to put it
all together we can see that for all
this to work several different things
have to be going on you have to have
variation in nature among the members of
a population you have to have natural
forces that can select for or against
the enhanced reproduction of individuals
who possess certain variations and you
have to have a mechanism by which those
selected variations get passed on
inherited by offspring and their future
generations these simple concepts are
essentially all you really need for
evolution to happen and from these basic
principles we get all the complicated
interweaving Xand interactions among all
the factors that become the underlying
drivers of Earth's biodiversity
you