Darwin’s voyage on the HMS Beagle to visit the Galápagos Islands in 1831 and his resulting theory of evolution proved to play an instrumental role in our understanding of the organisms on earth today, despite the extreme controversy of his theory at the time. He introduced the idea of natural selection, in which the animals that were best fit to the environment were most likely to survive and reproduce. We understand evolution by looking at three different aspects of an organism’s life: what the fossils of similar organisms look like, how the organism compares with other current species, and what kind of impact the environment had on the organism.
Evolution: Change in characteristics of living things over time.
Natural Selection: Organisms better fitted to the environment are more likely to survive and reproduce than organisms who aren’t fitted to the environment.
Fitness: How adapted an organism is to its environment.
Inheritance of Acquired Characteristics: Mistaken idea that animals whose traits changed in their lifetime could pass on those traits to their offspring. For example, a giraffe’s neck can extend its lifetime and pass the trait for long necks to its offspring.
Artificial Selection: A human practice to select certain traits wanted in a certain species.
Comparative Anatomy: Study of the differences and similarities between different species.
Homologous Structure: Organisms that have similar structures to organisms of other species because they descend from the same ancestor.
Analogous Structure: Animals with analogous structures inhabit the same types of environments, or perform tasks that require them to have a certain trait. These animals must then adapt, causing them to have similar traits that perform the same job, but this does not mean that their evolutionary history is related to each other.
Comparative Embryology: Study of the differences and similarities between different species as embryos.
Vestigial Structure: Structure found in an organism that has no obvious use.
Biogeography: The study of the environmental role of why animals live in a certain area.
Adaptive Radiation: Process by which a single species evolves into many new species to fill available niches.
During Darwin’s trip to the Galápagos Islands located off the coast of South America, Darwin observed that the individual islands differed from each other in climate and soil. He also observed that the plants and animals on the islands differed. The tortoises on different islands had different shells, and it was possible to tell which island the tortoise came from by looking at the shell.
Darwin’s observations helped him formulate his theory of evolution:
Natural selection explains the great diversity of life.
Humans can affect the evolution of a population or species by artificial selection. Artificial selection works much like natural selection does, but with humans, instead of nature, favoring specific traits.
For example, wolves were bred so that certain desirable traits would show up in the offspring. After thousands of years, these wolves evolved into the domesticated dogs we have today.
An organism does not have to be perfectly adapted; it just needs to beat the other organisms.
We can look at an animal’s evolutionary history by studying the fossil record.
We can also use comparative anatomy to compare one living species with another and figure out how these species evolved.
Comparative embryology compares living species at the embryo stage. Because embryos can have traits that do not appear in the organism in adulthood (vestigial structures), it is beneficial to compare embryos of different species because then one can tell if the two species ever had the same traits, or were related as a result of having the same traits.
DNA comparisons can also be used to understand how species evolved.
We can use biogeography to understand an animal’s environment and the environmental niche the animal must fill.
Figure: Here is a picture of the finches Darwin observed on his trip to the Galápagos Islands.The beaks of the finches are slightly different from each other because each of the islands on the Galápagos have different environments and therefore different foods. The finches adapted their respective environments, thus changing their physical features.