Evolution. It's a word that shows up in a lot of games and cartoons some of which one of us is quite into but tends to be used in a way that is often not really what evolution means in biology. Unlike what you might see in a game where an individual character evolves, with biological evolution individuals don't evolve during their lifespan. And it's not just the misconceptions about evolution like that. Some of the vocab or terminology can be misunderstood.
I'm not sure if I'm saying this right now but I think it's a good thing that we're For example, our video that explains how theory means something different in science versus casual conversation. Or the word fitness. In biology, fitness is related to how many offspring are produced, meaning genes are getting passed down, so biological fitness is not how strong the organism may be. Or even the word evolution itself. In casual conversation, the word evolve might refer to products getting more complex.
For example, a product changes to have more advanced features, but in biology, evolution does not necessarily result in more complexity. Let's talk about what this video is going to focus on. We're going to define biological evolution along with some of its mechanisms such as natural selection and genetic drift, then we will look at different lines of evidence for biological evolution.
First, let's get a general definition for biological evolution. Biological evolution is the change in a population's inherited traits over generations. Let's talk about the word population because it is populations, not individuals, that evolve.
A population has multiple organisms of the same species. But even though they're the same species, there's variety in a population, right? Different traits. Those traits are coded for by genes. So altogether, there is variety in the gene pool in a population.
But mechanisms that cause changes in the population's gene pool can lead to evolution because inherited traits in the population are coded for by genes. Consider a population of grasshoppers. Same species of grasshopper, but there can be variety in this population.
In this particular population, some are solid green, some have orange spots, some have slightly longer legs, some have shorter legs. Let's illustrate some mechanisms of evolution that could occur with this population. First mechanism we'll mention, gene flow. Genes that move between populations, which can happen through migration.
This can impact the genetic makeup in the population. Mutations. They may be harmful, they may be beneficial, they may be neutral.
But mutations do occur and they are sources of changes in genetic material that can change the genes in a population. Genetic drift. This involves a change in the genetic makeup of a population due to a random chance event. In our grasshopper example, if a lawnmower happens to go through an area, which is generally not a good thing if you're a grasshopper, the gene pool of the remaining grasshoppers may not represent the original population's gene pool.
This can impact the genetic makeup in the population. Natural selection. If, in this particular environment, the green grasshoppers are better camouflaged than any other color of grasshopper, they may not be seen as well by predators.
So if they don't get eaten, they can survive and reproduce, passing on the genes that code for being green. In this particular environment, other varieties may not reproduce as frequently and would have lower biological fitness. The green grasshoppers, with their higher biological fitness, result in more offspring that carry the genes for the green trait.
This can impact the genetic makeup in the population over time as more and more green grasshoppers reproduce. So these are mechanisms of evolution as they impact a population's genetic makeup and the genes passed down can code for inherited traits. Evolution doesn't necessarily result in a new species, but it can.
More about that in our speciation video. Evolution has multiple lines of evidence. But let's explore some now.
So first, homologies. Several different homologies. When using homology in evolution, homology is referring to a similarity due to shared common ancestry.
First, molecular homologies. With molecular homologies, many immediately think of DNA, comparing DNA relatedness, which is definitely part of molecular homologies. But there's also the importance of looking at homologous amino acids and characteristics of proteins. So all animals are part of the domain Eukarya. Animals like termites and turkeys, sea slugs and snakes, emus and elephants.
Molecular evidence would support that these animals are more related to each other than they would be to a bacterium, for example. But in this assortment of animals I just gave, molecular evidence would also support that the turkey and emu are more closely related than the turkey and the termite. The turkey and emu share a more recent common ancestor. Next, anatomical homologies. In this category, we'll focus on homologous structures and vestigial structures.
Homologous structures. Consider this human arm in Dog Forlan. You will find similarity in not only the general arrangement, but also the components that make up these structures. These are inherited from a shared common ancestor.
It's important to note that they do not have the same functions. Functions don't indicate common ancestry. For example, a bird wing and an insect wing may both be used to fly, but That's not an indication of relatedness. A bird wing and an insect wing are not homologous structures as they weren't from a shared common ancestor that had wings, and structure-wise the wings are very different. I mean, the bird has bones for one thing.
So a bird wing and insect wing are what you call analogous structures. Same function, but not homologous. Vestigial structures. To explain this one, I first need to tell you about the algorithm that shows me videos because I imagine it probably shows me more chicken videos than the average person. Because I really like chickens.
Among many cool chicken facts that I could share, one is that some adult chickens actually have a claw at the top of their wing. Yep. It can be kind of hard to see with all the feathers, but for this chicken, it's a non-functional structure. And other birds can have it, not just chickens.
The claw on the wing is considered a vestigial structure. A vestigial structure is inherited from an ancestor, but generally the structure has lost all or most of its function. Moving on from anatomical homologies, Developmental homology.
Embryology studies the development stages such as embryonic stages and looks for similarities in development among organisms which can support shared common ancestry. In our animal video, we mention a phylum called Chordata. In this phylum, all the animals have something called a notochord, which they have at least in some stage of their development.
Some have the notochord for their whole life. Vertebrate animals, including humans, are all included together in Chordata and make up a large part of the phylum. During embryonic development, organisms in this phylum have similar development structures, including pharyngeal slits or pouches and a post-anal tail. Similarities in development can support shared common ancestry among these organisms in Chordata.
Now let's shift from homologies and move into another piece of evidence of evolution, the fossil record. A fossil can be remains, or an impression, or a trace of an organism that once lived. Fossils aren't just for animals, they can be plants, or fungi, or yes, even bacteria, most organisms don't actually leave behind a fossil because it turns out it matters the surroundings, the environment, the type of remains that are present because not every part fossilizes well. But for fossils that are discovered and continue to be discovered, there can be a lot of knowledge to gain about the organism. Fossils can reveal how characteristics might have changed in a population over time and build understanding about ancestral organisms that once lived.
Radiometric dating, which takes into account how long it takes radioactive isotopes to decay, can be used to determine the age of the fossil. One more we'll cover here, biogeography. Biogeography combines biology and geography. This looks at how organisms are distributed geographically on the planet.
And the way that they are distributed is supported by evolution that has occurred in the populations of organisms on the planet. For example, populations on an island. They can be quite unique in appearance. This is expected.
as the mechanisms of evolution have acted on them independently from the location where they originally came from. However, the populations on the island tend to be the most closely related to populations nearest them, whether from another nearby island or mainland near them, versus somewhere much farther away. It's also important to take into account factors like continental drift and plate tectonics. For example, marsupials in Australia and marsupials in South America are really far away from each other geographically, right?
But it turns out marsupials of South America and the marsupials of Australia have shared common ancestry. Why? If you go back to the time of Pangea, the continents were connected. If the continents separated, mechanisms of evolution acted on these populations separately. One last thing we want to emphasize, evolution is not done.
It's not some finished thing. Evolution continues to occur. Since it's over generations, it's easier for us to see it in action when the generations do not take long.
such as antibiotic resistance in bacteria. Check out our natural selection video for more. Well, that's it for the Amoeba Sisters, and we remind you to stay curious.