There is much support for the theory of evolution. This evidence comes from a variety of scientific fields and provides information that helps us trace changes in species over time. In this lesson, we’ll look at this evidence and explore how it supports the theory of evolution.
The Theory of Evolution
In another lesson, you learned about evolution, which explains that species living today are descendants of species from long ago. Charles Darwin observed this phenomenon and described it as descent with modification.
Evolution occurs on a large scale over a very long time, but it is not unlike you and your parents. You are a descendant of your parents but in a modified version; you are not exactly like them even though you came from a combination of their genes.Evolution is a hot topic these days. But despite the controversy, evolution is, in fact, the core theme of biology and has been studied extensively enough to be called a theory.
In science, a theory is much more than a simple explanatory idea. A scientific theory explains natural phenomena and has been repeatedly confirmed through experiments and observations. Evolution is a scientific theory because not only has it been studied and tested but we also have several different sources of evidence to support it.
The field of paleontology is important to the support and understanding of evolution. This is the study of prehistoric life, including fossils, footprints, and past climatic events. As organisms die, they become part of the ground.
Often they leave behind bones and imprints, which allow us to see what they looked like millions of years later.Because new layers of ground and fossil form on top of old layers, this fossil record forms a sort of biological timeline. The fossil record shows us the sequence of historical changes in organisms. We can visually see how organisms evolved over time, but we can also use radiometric dating to determine the age of rock and fossils.Of course, prehistoric organisms that did not form fossils are hard to study, so we can’t know everything about the history of life on Earth. But we do know some really interesting things, like that whales and dolphins likely evolved from four-legged land animals.
How do we know this? One piece of evidence that supports this is the body structure of both animals. They have flippers in the front that may have evolved from front legs, but they also have small, internal back limbs that likely evolved from legs once used on land.
Other evidence in support of evolution comes from biogeography, which is how species are distributed across Earth. This is what first suggested to Charles Darwin that species evolve from a common ancestor. Darwin observed the animals of the Galapagos Islands and noticed that they were very similar to the animals on the South American mainland but very dissimilar to animals on other islands that had similar environments.From this, he concluded that the animals on the Galapagos had migrated from South America and after a long period of time became new species as the populations adapted to their new environment.
This also helps explain why there are no polar bears in the Antarctic and no penguins in the Arctic despite both places being very icy and cold.
It makes sense that organisms that are related to each other will have similar features. You may have your mother’s hair or your father’s eyes. But you also have two arms, two legs, a mouth, and a nose, just like other primates, such as monkeys and apes.
This similarity in characteristics from a common ancestor is called homology.You can easily see this type of similarity if you compare the forelimbs of mammals. Humans, dogs, whales, and bats all have the same skeletal elements in this part of their body. The difference comes in the function of that limb.
A human arm serves a much different function than a bat’s wing, but the similarity suggests that at one time we shared a common ancestor that had a similar structure, and each organism’s forelimb evolved to meet different environmental demands. Because these structures come from a common ancestor but have different functions, we call them homologous structures.Embryology, the study of embryos, is another way we can compare evolutionary relationships in anatomy. Many organisms share similar structures that are only present during development, and these similarities suggest a shared common ancestor long ago. For example, all vertebrate embryos have a tail at some point during their development, though I bet you’d be hard pressed to find a tail on an adult human! Vertebrate embryos also have throat pouches that have different functions in adulthood. For humans, they become part of the throat and ears, but for fish, they become gills.
Comparative anatomy can be very useful but only to a certain point.
The relationship between organisms that are very distantly related can be difficult to link with anatomy, so we use molecular biology instead. This field uses biological change at the molecular level to describe the evolution of organisms. So instead of looking at anatomical homology, biologists look at DNA homology.
Just like you and your siblings will have very similar DNA because you are related, so will organisms that inherited their DNA from a long-ago common ancestor. The degree of difference tells us how distant the ancestor is.For example, your DNA is very similar to that of your parents because you inherited it from them.
Your children will also have DNA very similar to yours but less similar to your parents because they are not as closely related. Likewise, their children will have DNA that is even less similar to your parents because now there are multiple steps in the genetic lineage. The same happens over evolutionary time periods, so comparing DNA can tell us how closely related organisms are and maybe even how long ago they shared the ancestor from which they are descended.
The support for the theory of evolution is overwhelming.
Many scientific fields contribute to the study and understanding of how populations change over time to meet the demands of their environments.Paleontology tells us how species change through time by studying the fossil record. Biogeography tells us how species are distributed geographically, which helps us understand why similar environments do not always support the same species. Comparative anatomy allows us to visually compare the homology of organisms so that we can see how different environmental demands may have led to similar structures with different functions. And when organisms are very distantly related, we can use molecular biology to understand evolutionary change and homology on the molecular level.
When this lesson has been completed, you may be able to:
- Dispense knowledge of the theory of evolution
- Discuss the evolution of fossil records through paleontology
- Recall the geographic importance of biogeography
- Compare homology and embryology to comparative anatomy
- Acknowledge the fact that molecular biology helps explain some of what comparative anatomy cannot