History of Evolutionary Thought - Online Tutor, Practice Problems & Exam Prep

Charles Darwin and Alfred Russel Wallace independently formulated the theory of evolution by natural selection in the mid-1800s. Darwin's observations during his voyage on the HMS Beagle, particularly in the Galapagos Islands, led him to conclude that species adapt to their environments over time. Wallace, through his studies in the Malay Archipelago, identified similar patterns of species distribution. Both naturalists emphasized the role of environmental pressures in shaping adaptations, laying the groundwork for modern evolutionary biology and the understanding of genetic variation as a key factor in evolution.

Geological Thinking

Before we start talking about Charles Darwin and his ideas of evolution by natural selection, we just want to sort of take stock of where scientific thought was at the time that Darwin was working. Now we've already talked about Plato and Aristotle, their ideas of unchanging species and the great chain of being, that organisms are arranged on a hierarchy. Now those ideas largely dominated Western thought at least well into the 1700s. But in the 1700s, especially in the field of geology, there started to be some new ideas. So we're going to say here that in the late 1700s, geology was challenging ideas of an unchanging Earth.

Now there's going to be 3 names that we're going to talk about. Like anything in science, there are more than 3 people working on this, but there are three names that it's likely you may need to know. And those names are James Hutton, Georges Cuvier, and Charles Lyell. So let's go through them one by one. James Hutton was alive and worked in the 1700s, and he introduced this idea of uniformitarianism.

Uniformitarianism is the idea that geological processes today are the same as in the past. Alright. So what does that mean? Well, that means that if we have this picture of a mountain here and just to say that if you have a mountain like that, right, how did that mountain get there?

You need to invoke geological processes that you see on Earth today to explain that mountain. If you see the Grand Canyon, how did that get there? You need to use geological processes that we can observe to explain that canyon. So we're talking about things like earthquakes, things like erosion, and those things take a long time. So a key idea here is that change on Earth is very slow.

And once you put that together, a big takeaway ends up being that, well, if change is so slow and if Earth has these grand features on it, the Earth must be very old. Right? To get a mountain like that would take a very, very long time, and that change would happen very slowly. Now that the Earth is very, very old is a bit of a new idea at this time. Alright.

Next, we have Georges Cuvier. He's a Frenchman. He was born in the second half of the 1700s and largely worked in the 1800s. Now Georges Cuvier, he studied fossils. He's largely considered the father of modern paleontology, and he argued that fossil records show extinct organisms.

Now to illustrate that, we have a fossil here of a trilobite. These are organisms that used to be all over the ocean, millions of years ago, but we don't see anymore. Cuvier actually studied things like extinct giant ground sloths. These sloths in South America that were the size of horses or elephants and just aren't there anymore. Well, Georges Cuvier didn't actually subscribe to ideas of evolution.

He thought that species were fixed, that they didn't change. But his idea that things went extinct is a big idea, and this tells us that life today is different. Life is different today than it was in the past. Right? And if you think, well, there are different things here than there used to be, that at least starts to open the door to the idea that species are changing.

Well, in the 1800s, we have this geologist, Charles Lyell. And Charles Lyell takes all of these ideas and puts them together and modernizes them some and writes this book. And it popularizes modern geological thinking in the book "Principles of Geology." And "Principles of Geology," which we show in this little book right here, was a hugely influential book in the scientific community.

It's especially influential because it is the book that Darwin brought with him on his voyage. And later in their lives, Charles Lyell and Charles Darwin actually become close friends and colleagues. Alright. Now if you need to remember these names, we've used alliteration to try and help you a little bit. We have this:

Hutton had the idea. Cuvier came with the fossils. And Lyell laid it all out. Alright. We're going to practice this more in problems to come.

I'll see you in the next video.

Whose book “Principles of Geology” most directly influenced the thinking of Charles Darwin?

• A. Georges Cuvier.
• B. Charles Lyell.
• C. Alfred Russel Wallace.
• D. James Hutton.

Which scientist was one of the first proponents of uniformitarianism and suggested the Earth was much older than a few thousand years?

• A. Georges Cuvier.
• B. Charles Lyell.
• C. Alfred Russel Wallace.
• D. James Hutton.

Which scientist specialized in fossils and has been called “The Father of Paleontology”?

• A. Georges Cuvier.
• B. Charles Lyell.
• C. Alfred Russel Wallace.
• D. James Hutton.

Lamarck and Inheritance of Acquired Traits

We've now seen how by the early 1800s, geology was introducing these ideas of a changing Earth. But we want to take stock of where biological thought was at that time, so now we're going to talk about Lamarck and the inheritance of acquired traits. Alright. We're going to say here that by the 1800s, there was evidence for evolution. There were people arguing that species changed over time, but scientists could not explain how it happened.

And without a good explanation for how it happened, those ideas just really weren't gaining traction. Now this makes sense because, remember, genetics and inheritance were not understood until the early 1900s. Right? Mendel does his work in the mid to late 1800s, but his papers aren't rediscovered until the year 1900, and that's when genetics becomes a science. Now, a little side note, one of the incredible things about Charles Darwin is he does figure this out without understanding genetics, but we'll talk about that later.

Alright. So into this world, we want to introduce Jean Baptiste Lamarck. He's a Frenchman, active in the late 1700s early 1800s, and he proposes a mechanism. It's really one of the first mechanisms to get some widespread traction, and his idea is based on two principles that we're going to talk about. Before we talk about them, I just want to make really clear though, Lamarck was wrong.

And he was wrong for a lot of different reasons. But as we focus in on these two principles, we want to see one specific way that he was very wrong, because understanding how he was wrong is going to help us understand how natural selection evolution actually works. Alright. So his two ideas here well, his first one is use, the idea of use and disuse. And he said that due to use, traits can become more or less developed in an organism's lifetime.

Alright. Now how Lamarck described this happening is not how it actually works, but the idea on its own isn't necessarily wrong. Right? If I'm always lifting weights with my right arm, and I never lift a weight with my left arm, you can predict what's going to happen. Right?

My traits, my muscularity, and my arms are going to become more or less developed in my lifetime. Alright. We're going to call those acquired traits. Right? That's something that I have acquired in my lifetime, as a big right arm and a little weak left arm.

Well, Lamarck then says the inheritance of acquired traits can happen. Right? He's going to argue that traits that develop through use or disuse can be inherited. And this is the part that is definitely very wrong. Right?

If I have a huge muscular right arm and a little weak left arm, you don't expect my kids to be born that way. Alright. So let's look at an example of Lamarckian thought here, and this is something that Lamarck actually wrote about. Trying to answer this question of why do kangaroos have such big hind limbs and such small little forelimbs? Alright.

Well, Lamarck surmised that the kangaroo ancestor probably had more equally sized limbs, and so this is, you know, here we have a proposed kangaroo ancestor, and like most things that walk on four legs, right, the front and back limbs are about the same size. Well, Lamarck then said, well, through use and disuse well, use, the kangaroo starts jumping, and that causes those hind limbs to get bigger and stronger. And disuse, well, if it's jumping on its back legs, the forelimbs were not used as much, and so they got smaller and weaker. And importantly, this is within one organism's lifetime. So we see here this organism starts jumping around, and its back legs get bigger, and its front legs get smaller from use and disuse.

Alright. And then the part that we're saying is really wrong is that he says the inheritance of acquired traits. He's going to say that this kangaroo that jumps around like this, its offspring will be born with bigger, stronger hind limbs and smaller, weaker forelimbs. And so that's what we see in this image here. Alright?

That's the part that we know is definitely incorrect. Alright. So the takeaway here, Lamarck was wrong. Changes that occur during an organism's lifetime are not inherited. Alright.

Today, we know what is inherited is genetic variation. Okay. We're going to look at Lamarck's ideas a little bit more and examples and practice problems after this. I'll see you there.

History of Evolutionary Theory Example 1

This example is talking about the fiddler crab, and it says that the fiddler crab shown below has one large claw and one small claw. How might Lamarck explain this observation? Right. So here we see this image of the crab, and we see this is the big claw, and then we have a little claw on the other side. Well, let's remember Lamarck's principles.

Right? We have use and disuse and the inheritance of acquired traits. Well, first off, let's think how would this crab start? How would this story probably start in this Lamarckian explanation? Well, I think the simple assumption would be that it would have claws of equal size.

Right? That would probably be the default. Alright. And then what about that idea of use and disuse? What would Lamarck likely say happened with this crab?

Well, he would probably say that it used one claw more, and in an individual's lifetime, we are going to say then that that claw got bigger. And then it would use one claw less, and that one, well through disuse, it got smaller. Alright, and then we have the idea of inheritance of acquired traits. So what would Lamarck then say? Well, we would say that the offspring would inherit one big and one small claw.

Alright. So though we need to remember that Lamarck was wrong, and we remember Lamarck today because of how he was wrong. So why is this so incorrect? Well, use and disuse, we are going to say that is not entirely correct. There are plenty of traits that do not become more or less enhanced by use, but certainly some do.

It is not completely wrong either. Where we want to identify him for being really wrong is this inheritance of acquired traits. We're going to say acquired traits are not inherited. Right. Today, we know that the genetic variation that we are talking about or the variation we are talking about in evolution, we need to talk about genetic variation.

Not variation that can develop during an organism's lifetime. Alright. More practice after this. See you there.

Lamarck developed his ideas almost 100 years before Mendel’s principles of genetics would be widely understood. With our current understanding of genetics, which of Lamarck’s ideas do we most clearly understand to be INCORRECT?

• A. In an individual, traits that are not used regularly will become less enhanced.
• B. In an individual, traits that are used regularly will become more enhanced.
• C. Characters acquired in an organism’s lifetime can be inherited by offspring.
• D. Populations will become more adapted to their environments over time.

Certain dog breeds regularly have “docked” tails, where a dog’s tail is cut to a short length while still a puppy. A breeder of rottweilers tells you that docking has become so common in this breed that they think puppies will start being born with short tails. Evaluate their thinking.

• A. Because only dogs with docked tails are reproducing, puppies are likely to be born with short tails.
• B. A docked tail would be considered an acquired trait, and therefore, you would not expect it to be inherited.
• C. Docked tails will become more common if they help the dogs perform certain tasks.
• D. Short tails are unlikely to become common in puppies because a docked tail mainly affects a dog’s appearance.

Darwin and Wallace

It's now time to talk about Charles Darwin and how he came to his idea of evolution by natural selection. But you'll notice here our title is actually Darwin and Wallace, and that's because in the mid-1800s, two naturalists came to the same conclusions about evolution. Alright. So, we're going to talk about Darwin first. Let's introduce you to him.

Well, Darwin was born in 1809. Interestingly, he's actually born the exact same day and year as Abraham Lincoln. Darwin, however, is from a wealthy family of intellectuals. His grandfather, Erasmus Darwin, is a very famous physician and poet, who actually wrote his own ideas about evolution. Now, Darwin himself is training to become a physician, but doesn't like it very much, and he faints at the sight of blood.

So he switches his studies to become a parson, which is basically like a minister in the Church of England. He graduates from doing that, but what he really likes doing is studying nature and collecting beetles, a popular pastime at that time. Then in 1831, the ship, the HMS Beagle, is going to go on a surveying expedition to South America, and they put out an ad for a naturalist, someone who will study the geology and the organisms along the way. Darwin convinces his dad to let him go. Now this is actually a pretty big ask because this naturalist has to pay their own way, and Darwin's dad ends up spending, in today's dollars, a few $100,000 paying for Darwin to go on this trip.

But, of course, it's hugely influential. So, the boat leaves from England. It goes to South America, and along the way, he's making all these observations. He observes fossils. So he actually digs up fossils of the extinct giant ground sloth, the same organism that others have talked about.

And Darwin sees firsthand how the Earth in the past is different from the Earth that we see today. It travels to Chile. And, in Chile, when he's there, he experiences one of the largest earthquakes in modern human history. And he sees how that can change the land, just how Hutton and Lyell said it could. He goes to the Galapagos Islands, and Darwin sort of recognizes, using the ideas of Hutton and Lyell, that these must be kind of young volcanic islands.

And its unique organisms, we're going to say here, on the Galapagos, that make a big impression on Darwin. Right? Things like Darwin's finches. All these different species of birds on these different islands that, in some ways, are very similar to each other, but you don't see anywhere else on Earth. The marine iguanas, these iguanas that swim in the ocean that eat algae that you don't see anywhere else, the iconic Galapagos tortoises.

And Darwin's wondering, why are these young islands so weird? Why are the organisms here so weird? And he rightly surmises, well, if these are new islands, maybe these are the first organisms to get there, and they colonized it and changed to live in this environment. Well, Darwin the boat ends up sailing all the way around the world, and by the time he's getting back to England, he's putting these ideas together. But he realizes this idea, it's a big one, and it's going to be controversial.

So he wants to make sure he has the facts to back it up. He spends the next 20-plus years researching and developing this theory, and in that time, he only tells a few of his closest friends. Now in that time, he also writes a book about traveling around the world, a popular book. It makes him quite famous. He's already quite rich, becomes a very famous scientist.

He's living the life of a wealthy intellectual scientist. And then in 1858, Darwin receives a letter from Alfred Russel Wallace describing a theory identical to his, the theory that Darwin has been working on for all these years. Now Wallace is someone that Darwin knew. They've been exchanging letters. So, let's introduce you to Alfred Russel Wallace then.

Alfred Russel Wallace, well, he's kind of like the working-class Darwin. He's 14 years younger than Darwin. He has a limited formal education. He comes from a family of surveyors. He's trained as a surveyor, but the family businesses tend to fail.

He's teaching, surveying. What he really likes doing is being out in nature, collecting organisms, collecting beetles. And he and a friend decide, you know what? Let's just do it. And together, inspired by people like Darwin, they travel to the Amazon.

And he spends 4 years going up and down the Amazon and the Rio Negro River, charting it, collecting organisms. He almost dies several times. His brother comes to visit him, gets yellow fever, eventually dies. And so, apparently, Wallace gets out of there on a boat back. The boat catches fire, sinks.

He loses all his collection. He does manage to survive and make it back to England. And 2 years later, he goes on another expedition, this time to the Malay Archipelago, what we think of today as Malaysia and Indonesia. Well, here, he's going around from island to island, and he observes the distribution of species. And kinda like Darwin, he's wondering, why are these islands so weird?

He's collecting organisms. He actually collects something like over 100,000 specimens. Now he has assistants, very talented locals who are helping him do this. But as he's doing it, he realizes well, he draws on this map a line, and this line is today known as the Wallace Line or Wallace's Line. And what he sees is that if you're sort of the south or east of this line, what we have here in yellow, these organisms on these islands are much more like the organisms from Australia.

Things like marsupials, like kangaroos. But to the north and the west, well, these organisms, they're much more like the organisms from Asia. Things like tigers and orangutans. Now some of these islands, you can see from each other. So why would you have such differences on islands that have such similar environments so close to each other?

Well, Wallace thinks if the organisms came from Australia and kind of changed along the way, and if the other organisms came from Asia and kind of changed along the way and sort of meet in the middle, that makes sense. And he, in his own words, has malaria. He's having a fever dream, and this idea comes to him. He writes it up, and he sends it to an elder scientist who he's been exchanging some letters with. He sends it to Darwin.

Well, Darwin gets this letter. He realizes that Wallace has had the same idea as him. He shows it to his friend, Charles Lyell, and they decide what they're going to do. Darwin very quickly writes up his own paper, and that same week, these two ideas are published together. Now, Darwin, remember, has been working on this idea for 20 years.

So he spends the next year writing and publishing his book 'On the Origin of Species'. Now because Darwin has been thinking about this and researching it for so long, that book is really well documented, and it's hugely influential in both the popular and scientific communities. So today, because of that book, we largely think of it as Darwin's theory of evolution by natural selection. But if we are being fair, we need to credit the idea to both Darwin and Alfred Russel Wallace. Alright.

We're going to dive into this idea in a lot of depth coming up. I'll see you there.

Of the following four observations, three were made by and strongly influenced Charles Darwin. Which observation was made by and influenced Alfred Russel Wallace?

• A. The distribution of species on islands in the Malay Archipelago.
• B. A large earthquake in Chile that caused measurable changes to the landscape.
• C. Fossils, including those of an extinct giant ground sloth.
• D. Differences between the finches on different islands of the Galapagos.

In 1858, Darwin received a letter from Alfred Russel Wallace describing a theory nearly identical to his theory of natural selection. How did Darwin respond?

• A. He ignored the letter and quickly published his own short paper.
• B. He immediately published his book “On the Origin of Species”.
• C. He quickly published his own paper jointly with Wallace’s letter.
• D. He published the letter from Wallace first, and waited to publish his ideas until he had finished his book “On the Origin of Species”.