Charles Darwin's 1859 book On The Origin of Species. Is considered one of the most influential texts ever published. But what did it actually say? Darwin had spent more than 20 years developing a theory of evolution, but he rushed to publish it once he learned that another man, the naturalist and commercial collector, Alfred Russel Wallace, had independently developed a very similar idea. Darwin knew the theory would be controversial, not just among scientists, but also among the general public. He was careful to lay out his argument very clearly using examples that would be familiar to most people. In The Origin of Species, Darwin makes three simple observations that were based on his experiences traveling aboard the Beagle, as well as the result of observations and experiments that he conducted around his home in England after his return. Based on these observations, he drew a deceptively simple and very important conclusion. Darwin's first observation was that there's variation among individuals within a species. This was based in large part on his studies of barnacles. Darwin had dedicated many years to studying the anatomy and taxonomy of barnacles, and that become the leading authority on these strange crustaceans. In fact, before Darwin's studies, scientists weren't sure whether they were crustaceans or some other form of animal. To complete this work, Darwin had meticulously sampled, observed and measured thousands of individual barnacles and had to figure out where to draw the line between closely-related species. It was clear to him that just as no two people are alike, not all individuals within a species of barnacles are alike either. Darwin pointed out that this is likely to be true for all species. Second, Darwin pointed out that some of that variation is passed from parents to their offspring. This was based in part on Darwin's observations of pigeons. He kept as many as 16 different varieties of pigeons in a custom-built outdoor coop and was fascinated by the different sizes and colors of their feathers. This variation had come about through selective breeding by pigeon fanciers, as they were known at the time. Who can make a profit by breeding and selling beautiful and interesting varieties. Darwin knew that a key component of animal breeding was the fact that many traits are heritable, meaning that they can be passed from generation to generation. How heritability worked was still a mystery, but it was nevertheless clear that offspring tend to resemble their parents. Darwin's third observation was that in every generation, more offspring are produced than can survive. During his voyage around the world, Darwin noted how individual animals and plants have to compete for limited resources like food and space. He had also read economist Thomas Malthus's essay about how human population growth is accelerating faster than the rate at which food is being produced. While Malthus was warning about a looming human crisis, Darwin realized that the same principle, competition for limited resources, leading to a struggle for existence, could apply to all species. Darwin's key insight came from taking these three observations and drawing a logical conclusion. He suggested that the traits present in the individuals that are most successful at survival and reproduction will become more common in future generations. He pointed out that this same phenomenon happens all the time in plant and animal breeding. Pigeon breeders select the individuals with traits that they want, like pretty feathers. They allow individual pigeons with those traits to reproduce. Because the traits are heritable, the next-generation of pigeons will have more birds with those traits. When applied to pigeon breeding, this wasn't really all that remarkable. Darwin referred to this process as artificial selection. Artificial in this case means that it's people that are selecting the traits that will become more common in future generations. What Darwin pointed out is that nature can do the exact same thing. When wild animals and plants reproduce, their traits are passed on to later generations. If there are certain traits that make some individuals more likely to reproduce, those traits will become more common in later generations. Darwin called this process natural selection. Interestingly, Darwin didn't use the term evolution at all in The Origin of Species. The word evolved appears just once. It's actually the last word of the book. Instead of using the word evolution, Darwin used the phrase descent with modification to describe the outcome of natural selection. He also didn't come up with the phrase survival of the fittest, which is often used as a way of describing Darwin's theory of evolution by natural selection. The phrase, survival of the fittest was coined by Herbert Spencer, a contemporary of Darwin's, and Darwin adopted it in later editions of The Origin of Species. Yet, I would argue that the phrase,"Survival of the fittest," can be misleading. The word survival usually refers to the survival of individuals. Yet Darwin's theory is about the persistence of traits over generations. Survival only matters because you can't reproduce when you're dead. Likewise, the word fittest seems to suggest that the most physically fit individuals are being favored by evolution. But that's not necessarily the case at all. An individual that isn't very physically fit, but nevertheless, reproduces will still pass their traits to the next-generation. While survival and reproduction are both important for evolution. Survival only matters because it gives individuals more opportunities to reproduce. Ultimately, it's a reproduction that matters most to evolution.
