How Are Animals Related? – The Family Tree of Life


Animals come in all different shapes, sizes,
and colors. From dogs to dolphins to caterpillars. And I think we know that some of them are
more closely related than others. But how do we figure that out, and how do
we know that they are relatives? Let’s look at how we figure out the great
family tree of Life! The Family Tree of Life When an animal is born it has genes from at
least one parent. Those genes will carry mutations. And when that animal becomes a parent itself, its
mutations will carry forward. But mutations do not go the other way, back
to the parent. This is really important. Let’s look at a population of squares. These are animals. It doesn’t matter what kind. One square has a mutation in its genes, and
it produces a modified protein that makes it yellow instead of green. As squares reproduce the yellow squares continue
to thrive alongside green ones. We know that all yellow squares are related
in some way, and none of the green squares share that particular gene. Now a yellow square has another mutation. This mutation does nothing, a simple duplication
of a boring gene sequence. It’s still yellow, it’s still fine. But that mutation circulates around as well. Let’s see what we have now. They are all squares, still in the same population. Some are yellow, so we know they are all descended
from the same original yellow square. Some are yellow with an additional marker,
so we know that they are all related. If we expand this sequence outwards and backwards,
we see some amazing things. Animals that appear unrelated share gene sequences. A weird example is the manatee, the elephant,
and the hyrax. We see evidence in their bodies and genes
that they are descended from a common ancestor. We might call them distant cousins on a very,
very big, very, very old family tree. An interesting technology related to this
is the molecular clock, which uses genetic mutations. The idea is that each mutation is random,
but they happen at a predictable rate. So if you know how many mutations there are
and have a prediction of how often mutations happen, you can figure out how long it has
been since two types of animals separated on the family tree. This is still a developing field, but might
be a source of interesting discoveries in the coming years. Here is what a family tree looks like. Each
branch is a group of species. Each split is a time when an older species,
like those squares from earlier, split into two populations and later into two groups
of species that have different traits. The common ancestor developed a backbone,
then later its descendants split into fish and non-fish. They developed four legs, then their descendants
split into amphibians and non-amphibians. And so on. But we do this the same way as with the squares. All these share the trait that there is a
membrane around the developing baby, whether it’s in an egg or in the mother’s body. We know this tree is accurate when it has
all the related species of a particular branch, including the original and all its descendants. The group called “Birds” is accurate this way. So that’s nice. But even within the group of birds we have
all kinds of groups that are complex tangles that we keep trying to unweave. Life keeps us guessing sometimes. The family tree stretches backwards for as
long as life exists. Most branches went extinct long ago, their
last descendants dying out without the chance to pass their genes forward. Every animal, plant, and bacteria is one of
the branches that is still represented today. One thing to notice here: humans are all related. We’re all at one end of one branch among the
millions of species that are on Earth. It’s worth considering how we treat each other
and how we treat the other species that live with us one the planet. After all, we’re family! Thanks for watching again this week. If you want more clearly explained biology,
you can watch other videos on this channel. And subscribe so you can know when a new one
branches out. Thanks for stopping by this week to learn
what makes Life awesome!

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