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AP®︎/College Biology
Discovering the tree of life
Discover the link between evolutionary trees and biodiversity. Video by California Academy of Sciences.
Want to join the conversation?
- Does any one here know why some sand dollars do have the holes in them? I've always been curious on that. This video made me remember finding them at the beach and wondering why some of them had holes in the top of them. Any input is appreciated.(7 votes)
- From what I read, the holes are used for gas exchange(3 votes)
- what do people do to conserve biodiversity(4 votes)
- Some conservation/restoration biologists focus on conserving biodiversity hotspots. Aka areas with large amounts of biodiversity. Some examples include Madagascar, New Zealand, and Australia. By focusing on a particular ecosystem, it can help protect many species.(7 votes)
- At, the video stated that sand dollars are flat sea urchins. From what I know, sand dollars are actually the skeletons of sea urchins. Could somebody please clarify what the actual difference is? 2:08(4 votes)
- Maybe this can clarify it a little bit. Sand dollars and sea urchins both belong in the sub category echinoderms (sea invertebrates with tube-like feet, spiny skin, and symmetrical bodies). However, sea urchins are in the subgroup regular echinoderms and sand dollars are in the subgroup irregular echinoderms (meaning they have altered symmetry).(6 votes)
- where did biodiversity come from?(3 votes)
- Biodiversity comes from life. (this is just a thought) From the predators, competition, and change comes evolution, and from that, springs biodiversity.(3 votes)
- do sea urchins have holes like sand dollars?(2 votes)
- "Who wouldn't want to think about sea urchins?" 🤣(1 vote)
- Sea urchins are the greatest. I've never stopped thinking about sea urchins! XD(2 votes)
- Does any one here know why some sand dollars do have the holes in them? I've always been curious on that. This video made me remember finding them at the beach and wondering why some of them had holes in the top of them. Any input is appreciated.(1 vote)
- what do people do to conserve biodiversity(1 vote)
- i guess people preserve endangered species and stuff...(1 vote)
- how do you hit the griddy?(1 vote)
- Do trees evolve over time?(1 vote)
- Species of trees are evolving, individual trees are not. Individual organisms do not evolve, populations evolve over generations.(1 vote)
Video transcript
(light music) - [Instructor] We're
looking at the main types of biodiversity, genetic,
ecological, and evolutionary. Here we want to really focus
on the latter, talk about evolutionary lineages. Something that I live
and breathe in my own scientific research. The study of evolutionary
lineages is nothing less than analyzing biodiversity over time. We always want to know where
did biodiversity come from, where is it going and
what is the role of humans in the future of these patterns. Lineages allow us to look
at the evolutionary history of different species, so the
study of evolutionary lineages is also the study of the tree of life. Scientists use that tree
metaphor to depict actual relationships among organismal
groups in a branching diagram, but how do you make
that diagram, what do you need to know that will
allow us to assemble that tree of life? What we're talking about
is a science known as phylogenetic systematics. Phylogenetic patterns are
made up of characters, features you can observe in organisms. Sounds pretty simple but
what it really means is that a unique feature of an
organism represents a unique event in the evolutionary
history of that organism an event that marks the first
appearance of that feature. And if you look at several
organisms and list the unique features of those organisms,
you are actually looking at the unique events in their
histories that tell you something about their relationships. This is because these events
can be shared with other organisms, if they are shared,
their histories are shared. In other words the species are related. Think about sea urchins for
example, who wouldn't want to think about sea urchins,
they're pretty neat animals, they have long spines, nice
rounded bodies supporting those spines, but did you
know that sand dollars are basically flat sea urchins
that have adapted to life on the beach, which I think
is pretty nice work if you can get it. So if sand dollars are sea
urchins, can we identify some evolutionary novelty that
joins all the sand dollars together to the exclusion of
all other types of sea urchins? Can we put them together
in a single lineage? Here's our sea urchin and
here is our sand dollar, but here's another type of
sand dollar, the obvious feature that links these
two guys is that they are as we said, really flat but
no other sea urchins are flat like this, that's a character
that uniquely connects all of the sand dollars
together to the exclusion of all other sea urchins. A feature that's arisen only
once in the evolutionary history of the sea urchins
that led to the sand dollars. The suggestion is that
these two guys share common ancestry, a common history
because right at this point they evolved as
characteristic of being flat. With the sand dollar group,
all of which we now know share a common ancestry, you
can have further elaborations on this flat form. For example, some will have
weird holes through their bodies that also represent
unique evolutionary events within the sand dollar grouping. And this is another critical
thing to recognize about the tree of life. Every group is nested or
included within another group, nature is a hierarchy that
can be represented by these branching diagrams,
diagrams known as cladograms or phylogenetic trees. But things can be really
complicated, we know that there is some 250 living species
of sand dollars and over 750 extinct fossil species. We also know there's a
single phylogenetic tree for sand dollars showing
how they're all related one to another. But we don't know the precise
shape the branching order also known as the topology of that tree. Each sub-grouping can be
supported by a unique evolutionary novelty or even several
if you have lots of data. The aim is to best arrange
all the unique characters to resolve or support
all of the relationships. Ultimately the idea is to
make a branch point for every single one of the relationships
so we can document the unique evolutionary
events or characters among all the species being studied. One thing that emerges from
all of this is the simple fact that some species
have appeared on earth more recently than others, you can
read this from the topology of the tree when you realize
that there's a time axis along here, oldest to most recent. The important thing is the
relative branching order, the topology of the tree. This branch point occurred
before that one and that branch point occurred before both of those. But let's face it, with ten
million species on earth, the tree of life can get
pretty complicated which is why it takes a lot of data and
a lot of studies to place as accurately as possible each
group of organisms on that big tree. So for phylogenetic
systematics, you need to use a computer, taking lots
and lots of character data, coding character traits
for every species in your analysis and feeding that
into a computer program. There are mathematical
processes to produce trees that can be tested and tested
again with new characters with the aim of arriving
at the most supportable hypothesis for the topology of the tree. Sometimes these new
characters can lead to changes in the branching order of the tree. And there's something
relatively new on the scene to help phylogeneticists
test these hypotheses of relationships and
that of course is DNA. Evolutionary pathways and
novel features are recorded just as much in DNA as they
might be in the physical traits of an organism that
you can see with your eyes. Phylogeneticists rely more
and more on the analysis of large amounts of molecular
data to develop trees. With the grand view of these
trees in hand, you get an even more powerful way of looking
at how evolution happens you can actually read life's
history book which I think is one of the most exciting
things you can possibly do in this field of study. For example, in the case of
the sand dollars, I can explore why they got flat or why
they have these bizarre holes in them, using the tree to
tell a story of evolution, it's what I live for in my science. One of the first ever
cladograms appeared in the work of none other than Charles
Darwin, who recognized the importance of evolutionary trees. I always think of old
Chuck when I think of this grand picture of life, this
grand picture of biodiversity and how trees show that. Darwin knew that these
trees reveal lineages and big picture biodiversity
against a background of enormous time. What he didn't know was
just how powerful our modern techniques could become in
telling a spectacular story and how useful these trees
are in helping us protect earth's amazing but
threatened biodiversity. (light music)