Hi. It's Mr. Andersen. And in this podcast I'm going to talk about evidence
of evolution. Evidence laid down by this guy, who you all probably know as Charles Darwin.
Who you don't know is this guy over here. This is Alfred Wallace. And these two both
came up with the same exact idea. That the diversity of life on our planet comes through
the process of evolution. And the mechanism by which that occurred is natural selection.
Now why don't any of us know Alfred Wallace? Well if you're interested in the story of
Darwin, a great read would be David Quammen's The Reluctant Mr. Darwin. David Quammen actually
lives here in Bozeman. And I have met him. He's a fascinating author. But basically lays
out the life of Charles Darwin as this scientist who loved to work on the minutia of science
and gather data over years and years and years and years to eventually support his ideas.
To support his theory of natural selection. And he did that. For 30 years he sat on the
idea of evolution and natural selection. And he never published anything. Until he got
a letter from this guy, Alfred Wallace, who'd gone on a similar journey to southeast Asia.
Discovered the same exact thing. Wrote a letter to Darwin. Darwin freaked out. He eventually,
they publish a letter together. And Darwin kind of gets all of his ducks in a row and
publishes The Origin of Species, where he lays out evidence of evolution. Since Darwin
started first and had kind of established this theory. Had a first. And he also knew
a lot of really powerful people. We remember his name. But it's still doesn't take away
from his work. It is amazing. So The Origin of Species basically he lays out evidence
for evolution and then a means by which that occurs. And that is natural selection. So
here's him coming up with the idea. So this is in one of his notebooks. And he took copious
notes on all of his ideas, was the idea that life started from one common ancestor and
it branched into all the forms of life that we have today. He then explained how this
could occur. Because a number of scientists had said this before. And he lays out a real
persuasive argument in The Origin of Species. And so he starts without talking about nature
at all. He started by talking about something that all of us can see within our lifetime.
At least through out generations. He starts with the pigeon. And if you look at this pigeon
right here, this pigeon was bred selectively by humans to create a number of different
pigeons. So let's look at all these different types of pigeons from this red pigeon to this
white pigeon to this really crazy beaked pigeon. All of these have the same DNA as that original
pigeon. Now there's going to be some variation. That's why we get all of these differences.
But most people wouldn't think that these all came from that same pigeon. And so that's
a great piece of evidence. That if we could do this in just hundreds of years using artificial
selection, surely we could do this in nature using millions of years. And so then he starts
talking about nature. The first thing he talks about is the idea of biogeography. And this
is the one thing that struck him. Because he went on a three year tour where he sailed
from Europe. He ended up down here in South America. They bounced around South America.
They went across the Galapagos. Sailed across the Pacific. Went to Australia. Went to all
of these islands. Eventually came back to South America and to Europe. And that whole
way he saw life. But he saw life not the same everywhere. In other words in Australia he's
going to see marsupial mammals. But if you look in North American we're not going to
have any marsupial mammals except for the possum. And so what biogeography is is where
life is found. And because before Darwin, all scientists believed in special creation.
That God simply placed everything perfectly evolved to where it lived. That's what the
scientists believed. And he started to question that. When he went to the Galapagos for example
and found that there were only one type of bird there, the finches. That there were only
the tortoises there. But you didn't have mammals. You didn't have goats and pigs and all those
things weren't there naturally. And they also had adapted to each of the individual islands.
The natives here could tell him they could identify what an island a tortoise comes from
just by the shape of its shell. And you can see right away there's clear differences between
these. In other words this one right here is the last living tortoise from Pinta Island.
This is lonesome George. He has a really long neck. How did he get a long neck? Not by stretching
it Darwin said. But on Pinta Island where there's not a lot of vegetation, basically
tortoises that had a longer neck were able to get more vegetation and so their genes
were passed on. Likewise this down here is from Santa Cruz, this tortoise. And so there
probably are tortoises born on Santa Cruz that have a really long neck, but predators
can eat it because there's plenty of food. The big selective pressure ends up being the
predators. And so we have a bell shaped curve of neck length on tortoises. But it's going
to vary depending on what the island is. And so Darwin lays out a compelling argument that
life is different no matter where you go. And it has to do with chance and how it got
there. It just wasn't added there. Next he talks about fossils. And he collected fossils
the whole way. That was one of the big things. He brought back all of these fossils to England.
And he was able to lay out evolution. He was able to show how certain organisms changed
into other organisms. So a great example would be the horse. So the horse essentially went
from an animal that's kind of like a deer where it was living in the forest. And it
was kind of a browser. And then it moved over millions of years, became a grazer. And you
can see that its size got larger. And its teeth changed. And its legs changed. And so
the fossil evidence that Darwin had was not great back then but it still was compelling
enough to make the argument for evolution. Since this time you can think we're talking
about hundreds of years. We've gathered so many fossils that in science we've gathered
so much evidence, so much fossil evidence that in science evolution is pretty much accepted
as fact. There's not a lot scientists who would ever question it. He also talks about
homology. So homologies are going to be characteristics that show similar origins. And so if you look
at a human arm or a dog leg or a pigeon wing or a whale flipper, you can see that they
all have similar bone structure. Even though they do totally different things. This is
for swimming and flying and swinging from a tree. They all have the same bone structure.
That suggests that they came from the same origins. Because you surely could make different
ways to make an arm using just bones. But this had a common ancestor, a tetrapod that
shared this. So it passed on. If you have one of these, I have one of these, a point
on my ear. This is called a Darwin's tubercle. But basically it is the point at which used
to be the mammal tip of their ear. And it's been passed on through time. It doesn't serve
a purpose anymore but it's still there. And so homologies in structures were super important.
But what Darwin didn't have is a really thorough understanding of genetics. And he surely didn't
have an understanding of DNA. And so DNA, when it comes to evidence of evolution, is
the trump card. It is pretty much the definitive piece of evidence that shows us that evolution
has occurred. If you don't understand how DNA works, basically it's passed from generation
to generation to generation to generation. There are mutations in there which may be
selected for or against using nature. But basically that message gets passed from generation
to generation to generation. Example is the game of telephone. So in the game of telephone
basically this person tells this person a story. Whispers it in their ear which is passed
to the next and passed to the next. And so this is like generation after generation after
generation. So if we look through a quick game of telephone, maybe this person says
the fat cat ate the rat. And then red says the fat cat ate the rate. But yellow makes
a mistake and says the fat car ate the rat. And once we go forward now that message or
that mutation is stuck forever. Because we can't go back to that original message. And
so DNA holds a fingerprint for how mistakes are made and they're passed through time.
And so basically as more mutations come, let's go back for just a second, as more mutations
come we can actually trace through that message and we could figure out where those mutations
started. We also have started to figure out you can use the rate of those mutations. And
so we can actually add time to it. And so we could say right here is that magenta or
that purple mutation which would be way up here. And so basically what you can do is
you can look at one of these specific messages, the fat car ate the bat. We could say, okay.
Well it has this mutation here. It has this yellow mutation so we know that it's at least
past this. It also has the red mutation. So we know that it's at least past this. So we
could identify it as this person. Likewise with life we can compare the DNA of a human
to a chimpanzee to an orangoutang to a gorilla to a yeast, since we all share common ancestry
with all life on our planet. And we can say who is related to whom. And so that's a really
compelling piece of evidence that shows that not only is evolution correct, but we can
also measure the rate at which it occurs. And who's related to whom. And so again, it's
a long story. But it's also important because it guides all of biology. And I hope that's
helpful.