Chapter 7: The Science of Life
Now I must tell you more about the complicated fields of biology and psychology.
People have always studied plants and animals, for as long as people have existed. They studied all the same things you study about your own plants and animals. How do you breed better plants and animals? When is the best time to plant your seeds? How do you make your plants grow the best? What food do animals like to eat? Where is the best place to look for animals when you go hunting? What time of the year do certain animals come to your area? And so on.
Your ancestors and the Europeans and other agricultural people figured all those basic things out long ago. That was enough for people to grow their farms and feed their families.
But a few people were still curious to learn more. There were some things they didn’t understand well yet, so they kept studying plants and animals, because they thought they might be able to figure out more important things.
A big thing people still wondered about was why there were different kinds of plants and animals. They could see that children inherited characteristics from their parents. They could see that people could breed plants and animals to pass their characteristics on to the next generation. They could see that if they bred some animals or plants together that had certain characteristics, and they bred plants or animals together that had different characteristics, they would have two breeds of plants or animals that had different characteristics from each other.
If a farmer had some horses, he could breed lightweight, fast horses together to get more lightweight, fast horses. He could also breed big, strong horses together to get more big, strong horses. Now he has lightweight, fast horses, and big, strong horses. Then he could breed the fastest of the fast horses together and get even faster horses. He could breed the strongest of the strong horses together and get even stronger horses.
People could breed corn the same way. If a farmer had a field of corn and some of the plants grew sweeter corn cobs than the others, he could breed those plants with each other to make sweeter corn. Then he could breed the sweetest of those plants together to make even sweeter corn. Meanwhile he could breed the plants that had the biggest corn cobs together to make plants that grew bigger corn cobs. Then he could breed the plants with the biggest of the big corn cobs together, to make plants that grew even bigger corn cobs.
Farmers all over the world figured out how to do this. These scientists wondered if it was possible to breed plants or animals together for so long that they would turn into different plants or animals. If you bred fast horses with fast horses, and strong horses with strong horses, long enough, could you turn them into two completely different animals?
In the same way, donkeys and horses are very similar animals. Are those two different animals both descended from the same ancestors? Horses are bigger and faster than donkeys, but donkeys can climb better and can walk over rough ground better. Was there one ancestor species where the ones that were bigger and faster bred with each other, and the ones that could climb better and walk over rough ground better bred with each other, until they turned into two different animals?
If that had happened, the scientists had to answer two more questions. How long did it take? And, what made it happen?
Animals are different because they have different characteristics. Parents pass their characteristics on to their children. A breed of strong horses and a breed of fast horses have different characteristics, and donkeys and horses have different characteristics. The only difference is, fast horses and strong horses have a few different characteristics, and donkeys and horses have a lot more different characteristics. Breeding animals together makes their characteristics change slowly, but it does make their characteristics change. If animals’ characteristics change, that means one kind of animal could turn into a different kind of animal. Since their characteristics change slowly, that means that turning one animal into another animal would take a very long time. But no matter how slowly it happened, if it went on long enough, it could happen.
To answer the question of how long this breeding took, first you have to answer a different question. How old is the Earth? That will give you some idea how long plants and animals could’ve been breeding with each other. If the Earth isn’t old enough for plants and animals to have bred together long enough to turn into different plants and animals, then this couldn’t have happened.
For a long time, nobody knew how old the Earth was. Nobody had any way of finding out how old the Earth was. A lot of people thought the world was about as old as people were. The Old Testament of the Bible was written about 5,000 years ago, so a lot of people thought the world was about 6,000 years old.
If the world was only 6,000 years old, that wouldn’t be enough time for horses and donkeys to start out as the same animal and breed with each other differently until they became two different animals. So that idea wouldn’t work.
But nobody was sure how old the Earth was. Maybe the Earth was older than 6,000 years. Maybe there had been enough time for animals to turn into other animals.
Eventually, some scientists figured out how to build machines that would help them find out how old the Earth was. They discovered that instead of the Earth being 6,000 years old, it’s 4,500,000,000 years old. That would be plenty of time for animals to turn into other animals.
The other big question that had to be answered was, why would plants and animals that had certain characteristics breed with each other by themselves? People could make plants and animals do that, but people didn’t make plants and animals do that. If people didn’t do it, what else could’ve done it?
A great scientist named Charles Darwin figured out the answer to this. This was back before anyone figured out how old the Earth was, but he had a good idea that the Earth could be old enough for this to happen.
Charles Darwin lived in England in the 1800s. He sailed around the world in a sailing ship. He visited many places, saw many different plants and animals everywhere he went, and met a lot of different people everywhere he went.
He spent a lot of time in South America, and especially the Galapagos Islands. The Galapagos Islands was where he made his big discovery.
The Galapagos Islands are a group islands out in the middle of the ocean. That gave him some important clues no one could get in most other places.
First, the Galapagos Islands are isolated, out in the middle of the ocean. People didn’t live on the islands then, so they hadn’t brought their own animals with them. Also, the same animals had lived on the islands for a long time. New animals didn’t come to the islands very often.
Second, there were many islands, and they were close to each other, so the animals that did live on the islands had spread to all the islands. But because they were islands, the animals didn’t cross from one island to another very often.
What Charles Darwin discovered was that each of the islands had the same animals on them, but on each island, each type of animal had slightly different characteristics. In the same way that a farmer can make different breeds of horses, on the Galapagos Islands, each island had its own breeds of turtles, and birds, and lizards, and whatever.
Each island had a slightly different environment. Since each individual plant or animal of a certain type had slightly different characteristics, some of them would have characteristics that would help them survive and reproduce a little better than the others. Since those plants or animals could survive and reproduce a little better, they would have more children. Since they had more children, that would mean that more members of the next generation would inherit their characteristics. Then they would be able to survive or reproduce a little better than the other plants or animals, and then they would have more children. Then even more of the next generation would have the characteristic, and so on. Eventually the characteristic would spread to all of the type of plants or animals, so the whole group would have the new characteristic.
Since each island had a slightly different environment, and each individual plant or animal had slightly different characteristics, the characteristics that would help plants and animals survive and reproduce on one island would be slightly different than the characteristics that would help them survive and reproduce on a different island. That means that if the same type of bird or turtle or whatever lived on two different islands, certain characteristics would get passed down to more birds or turtles in the next generation on one island, and different characteristics would get passed down to the birds or turtles in the next generation on the other island.
Charles Darwin discovered a lot of things like the same type of birds living on two different islands who have different shapes of beaks. Birds might have different beaks because there were different insects living on the two different islands. Or the insects might be the same but the trees they lived in were different. Either way, the birds always had the shape of beaks that helped them catch their food the best.
The same pattern of cause and effect would work everywhere in the world. If the ancestors of horses and donkeys lived somewhere where there were plains and hills, and they could live pretty well in either place, some of the animals would live on the plains, and some would live in the hills. In order for all the animals to get as much food as they could, they would spread out to everywhere they could live pretty well, wherever there was food for them.
The animals that lived on the plains would need to be fast, because the plain would be flat, so they could run easily. All the other animals on the plain could run easily too, including the ones that would eat these animals. So out of the animals that lived on the plains, the ones that could run the fastest would survive and reproduce the best. So they would have the most children. Then out of their children, the ones that were the fastest would survive and reproduce the best again, so the third generation would be even faster. And so on. Just like the farmer could breed his fastest horses together, the environment on the plains, itself, would breed the fastest animals with each other. All the animals would try to breed with each other, and the ones that were the fastest would be the most successful, because the slower animals would be the ones that got eaten by predators the most.
Meanwhile in the hills, the animals that lived there would need to be able to climb well and walk across rough ground well. So the hills themselves would breed the best climbers with the best climbers. Again, all the animals would try to breed with each other, but the ones that could climb the best would be the most successful, because the ones that couldn’t climb as well would fall and kill themselves more often. So the best climbers would have the most children, and then the next generation of the animals would be better at climbing than the first generation.
This is called natural selection. The environment breeds the animals that are best at surviving and reproducing in that environment. When that happens for thousands or millions of generations, the animals on the plains turn into horses, and the animals in the hills turn into donkeys. This is another thing I meant when I said that the whole world is like a farm, but who are the farmers?
Charles Darwin called this evolution. Evolution is the cumulative adaptation to an environmental pressure. That’s just a fancy way of saying that the animals or plants that survive and reproduce best in an environment are bred for the characteristics that help them survive and reproduce, generation after generation. When that goes on long enough, two different groups of animals that had the same ancestors get so many differences between them that they can’t breed with each other any more. Then you say that the two animals are two different species.
Horses and donkeys are two different species, but they’re still a lot more closely related to each other than most other species. Horses and donkeys are similar enough to each other that they can still have children together—and their children are mules—but their children are sterile. Horses and donkeys can’t mix back together and turn back into the same species now, because mules can’t have children with each other. That means they can’t pass their characteristics down to the next generation, and that means that the mules that are the best at surviving and reproducing can’t pass their characteristics down to the most children of the next generation.
Every single characteristic of every plant or animal is a characteristic that either helps it survive and reproduce now, or else it helped it survive and reproduce at some earlier time. As farmers you probably know that your own plants and animals use most of their characteristics to survive and reproduce. The same is true for plants and animals all over the world. Whatever characteristics plants and animals don’t use to help them survive and reproduce are characteristics they used at some other time.