Darwin Brings his Ideas to the Public…
When Darwin came back to England in 1836, he brought back specimens from around the world. What he brought back started a buzz among the scientific world.
Darwin found that all the species he found on the Galapagos Islands were unique species to only that chain of islands. Although they looked similar to many species found on the South American mainland, the Galapagos species did have unique traits that made them separate and unique from the rest.
The Publication of “On the Origin of the Species”…
Darwin filled his notebooks with his ideas about species diversity and the ideas that would later form the theory of evolution. Although Darwin had seen many things that brought him to these ideas, he did not rush to publish his results. He knew that his ideas would challenge fundamental beliefs of his day.
Darwin shelved his research and told his wife to only publish his results on his deathbed.
In 1858, a naturalist by the name of Alfred Russel Wallace was doing research in Malaysia. In his essays he summarized his ideas on evolutionary change. This prompted Darwin to release his research after 25 years of waiting.
Darwin finally found freedom to write his thoughts. Eighteen months later, Darwin published his results in the book “ON THE ORIGIN OF THE SPECIES”.
In his book, Darwin proposed a mechanism for evolution called NATURAL SELECTION. His work caused an immediate sensation. Many people argued he was brilliant while others argued the he was sacrilegious and against all standards and beliefs of the day.
Natural Variation and Artificial Selection…
Darwin began his explanation of evolution by abandoning the beliefs that a species was perfect and unchanging. He explained that NATURAL VARIATION, the differences among individuals of a species, is found in all organisms.
Some cows give more milk than others, some plants produce larger fruit than others, and all humans look slightly different. Today, the fact that variation exists seems obvious, however in Darwin’s day, it was revolutionary to suggest that variation was a major feature of life.
Much of Darwin’s information and research was not done on the HMS Beagle, but back home in England studying farmers. He noticed that farmers regularly used variation to improve crops and livestock.
Though a technique known as SELECTIVE BREEDING, the farmers would determine which individuals to use for breeding based on the best traits they wanted to pass on. Only the fattest hogs or the cows which produced the most milk were chosen to breed. Eventually the offspring would be optimized. Darwin called this process ARTIFICIAL SELECTION.
Artificial selection was used to produce many of the species of plants that we know of today as well as many species such as dogs, cats and many livestock.
In Artificial selection, nature provided the variation among the animals and it was humans who selected which variations to breed.
The Struggle for Existence…
Darwin set out to convince the public that there were processes, much like artificial selection that were at work every day in nature. To help prove his point, Darwin looked back at Malthus’s work on population growth.
Darwin realized that high birth rates and a shortage of life’s basic needs, such as food, water, shelter, etc, would eventually force organisms into a competition for these resources. This competition is what Darwin coined, the “STRUGGLE FOR EXISTENCE.”
In this struggle, the predators that are faster or specially adapted, have a better chance of catching more prey. And the prey who are faster, better camouflaged, or better protected, would avoid being caught. This was a central point in Darwin’s theory.
Survival of the Fittest…
A key factor in the struggle for existence was how well suited an organism was to its environment. Darwin called the ability of an organism to survive and reproduceitsFITNESS.
Darwin said that an organism’s fitness is the result of ADAPTATIONS, which are any inherited characteristic that increases an organism’s chance at survival.
These adaptations allow an organism to be better suited to their environment, and thus better able to reproduce and survive.
Adaptations can include the following…
-Porcupine Quills – for protection
-Lion Group Hunting– better chance for food
-Poison Arrow Frog Bright colors – for warning signals
-Primates Opposable thumb - grasping
The concept of fitness, was central to the process of evolution by means of natural selection. Generation after generation, organisms compete to survive and produce the better offspring.
For example, in a birds nest, there are many factors, which lead to a baby bird surviving or dying. Baby birds which are best adapted are able to get food, and out-compete the other birds, allowing them to survive and grow-up. Any baby bird not well adapted will either die off or be thrown out of the nest. In other words, individuals who are better suited to their environment survive and reproduce the most successfully. This is known as SURVIVAL OF THE FITTEST.
Because survival of the fittest held so many similarities to that of artificial selection, Darwin called survival of the fittest, NATRUAL SELECTION.
Over time, natural selection results in changes in the inherited characteristics of a population. These changes then increase a species’ fitness in a given environment.
Although we cannot see natural selection directly, it does take place in a population over many, many generations.
Descent With Modification…
Darwin said that over long periods, natural selection produces organisms that have different structures, establish different NICHES, or occupy different habitats. As a result, species today look very different from their ancestors from the past.
Each living thing has descended, with changes from other species over time. We can look at it as an evolutionary family tree. He referred to this principle as DECENT WITH MODIFICATION.
This principle implied one thing that did not sit well with many people of the time…All living things are related to one another.
If we look back in time, we can see that there was a common relative between tigers, panthers and lions. And farther back, you can see that these felines share a common ancestor with horses, dogs, bats, and primates.
Even farther back than that, we can see common ancestors linking mammals, fish, birds and reptiles. If this logic was followed, the farther back you went, the more all life would have common ancestors, until finally, all life would be linked by one common source.
This was known as COMMON DESCENT.
Looking at all this, a single “tree of life” can be formed, linking all life on Earth.