9 minutes
Published May 2013

What is Natural Selection?

Transcript

What is Natural Selection?

Natural selection is one of several key concepts contained within the theory of evolution. To understand exactly what natural selection is and why it’s important, let’s first take a quick look at two other evolutionary concepts: descent with modification, and the overarching idea of common descent.

Descent with modification is the observable fact that when parents have children, those children often look slightly different than their  parents and slightly different than each other.

Common descent is the idea that all living things on earth are related, they descended from a common ancestor. Through the gradual process of descent with modification over many many generations, a single original species is thought to have given rise to all the life we see we today.

The common descent of all life on earth is not a directly observable fact. We have no way of going back in time to watch it happen. Instead, common descent is a conclusion based on a massive collection of facts. Facts found independently in the study of fossils, genetics, comparative anatomy, mathematics, biochemistry, and species distribution.

Because the evidence for common descent is so overwhelming, the concept has been around since ancient times but in the past it was rejected by many philosophers and scientists for one main reason: You can not get order and complexity from random chaos alone.

The bodies and behaviors of living things are extremely complex and orderly, but descent with modification produces random variation.

All through history, no one could explain how complex life arose from simple life through random variation, until Charles Darwin discovered natural selection.

All through history, no one could explain how complex life arose from simple life through random variation, No one until Charles Darwin and his discovery of natural selection.

Charles Darwin who lived from 1809-1882 was a naturalist - someone who studies nature. At the start of his career he traveled the world by ship, collecting and documenting plants and animals.

During his travels, Darwin became very interested in the idea of common descent. He noticed that Islands contain species of plants and animals unique to those islands - they can’t be found anyplace else on earth - but they often look and behave surprisingly similar to creatures found on nearby continents.

Tortoises on the Galapagos Islands can be distinguished from those of Africa, meanwhile, with the exception of size, they’re almost identical to a species found nearby in South America.

Darwin believed these similarities could be best explained through common descent. Long ago a tortoise from the mainland may have drifted to the islands, possibly on a raft of storm debris, and once arriving, laid her eggs. Random changes caused by descent with modification over thousands of years eventually transformed the island creatures and the mainland creatures so much, that they could no longer be considered the same species.

This idea made good sense to Darwin except for one thing. The island creatures he found weren’t just randomly different from their mainland cousins, they were specially adapted for island life.

The Galapagos is a collection of 18 main islands; many of which are home to tortoises. The larger islands have lots of grass and vegetation. Tortoises there grow extra heavy and have dome like shells. Some of the smaller islands have very little grass, forcing tortoises to feed on island cactus. The best cactus pads grow on the tops of these plants. Fortunately, tortoises on these islands are equipped with expanded front legs and saddle like shells allowing them to stretch their necks extra long to reach their food.

It’s almost as if these island creatures have been perfectly sculpted to survive within their unique environments.

How did this sculpting take place? Random descent with modification alone could never do such a thing.

Darwin drew upon his knowledge of selective breeding to answer this question. For thousands of years, farmers have been taking wild plants and animals, and through the process of selective breeding, have sculpted the original wild forms into new domestic forms much better suited for human use and consumption.

The process is slow but simple: If a single plant produces 100 seeds, most will grow to be nearly identical to the parent plant, but a few will be slightly different. Some variations will be undesirable -  smaller size, bitter taste, vulnerability to disease and so on. Other variations will be highly valued - thicker sweeter leaves for for example.

If a farmer only allows the best plants to reproduce and create seeds for the next crop, small positive changes will add up over multiple generations, eventually producing a dramatically superior vegetable.

You might be surprised to hear that broccoli, cauliflower, kale, brussel sprouts, and cabbage are all just different breeds of a single type of weed commonly found along the shores of the English Channel. The evolution of this original plant into all the varieties we see today, was carefully guided by different farmers around the world, who simply selected for different traits.

It’s important to note that the farmer doesn’t actually create anything. Random descent with modification creates new traits. The farmer simply chooses which of the new creations are allowed to reproduce, and which are not.

Darwin proposed that nature itself is also capable of selection. It may not have an intelligent brain like a farmer, but nature is an extremely dangerous place in which to live. There are germs which can kill you, animals that can eat you. You could die of heat exhaustion, you could die of exposure to the cold.

When parents produce a variety of offspring, nature, simply by being difficult to survive in, decides which of those variations get to live and reproduce, and which do not. Over multiple generations, creatures become more and more fit for survival and reproduction within their specific environments. Darwin called this process: natural selection.

Since Darwin first put forth his idea in the mid 1800’s, natural selection has been studied and witnessed numerous times in nature and in the science lab. What started as an idea is now officially an observable fact.

Darwin's discovery has greatly expanded our understanding of the natural world. It’s led to countless new breakthroughs and it finally allowed scientists to seriously consider the idea of common descent.
 
So to sum things up, what exactly is natural selection?

Natural selection is the process by which random evolutionary changes are selected for by nature in a consistent, orderly, non-random way.

Through the process of descent with modification, new traits are randomly produced. Nature then carefully decides which of those new traits to keep. Positive changes add up over multiple generations, negative traits are quickly discarded.

Through this process, nature, even though it does not have a thinking mind, is capable of producing incredibly complex and orderly creations.

I’m Jon Perry, and that’s Natural Selection Stated Clearly.