Course 3 explores biology in a bigger scale, and in these first two modules, we've discussed evolution. The first module discussed what evolution is and how it works, and then in this module, we talked about how evolution leads to the generation of new species through a process called speciation. Evolutionary processes and speciation are responsible for the wide variety of life that we see on Earth. Although there are biodiversity hotspots like the Amazon rainforest, living somewhere exotic is not a prerequisite for finding biodiversity. It can be as simple as hanging up a bird feeder. This is my bird feeder, and this is a hairy woodpecker sitting on my bird feeder. Every time we go inside, every time we look out the window, it's an opportunity to notice the rich biodiversity that is all around us. One of the things we'll be focusing on in the second part of this course is how we are interconnected with the life all around us, the study of ecology. Biodiversity isn't just the animals that we can see, it's the plants too. Biodiversity also refers to how many different living things there are in an area, and if some are more or less represented. Biodiversity also includes genetic diversity. Maintaining genetic diversity is also an important part of biodiversity. Without sufficient genetic diversity, maintaining species can be challenging and can ultimately lead to extinction, which is the loss of a species. Evolution works because of genetic variability. In the event of some catastrophic incident, because not all organisms are identical, at least a few members of the species are likely to survive because they have some kind of advantage. Although this could eventually result in the formation of a new species, without a certain level of variation, it is more likely that all members of the species will go extinct. Genetic diversity is also important for keeping species healthy. For instance, remember in the last course, we talked about dominant and recessive genes. Many diseases are caused by recessive genes, but you won't get sick if you only have one bad copy, you need to have two bad copies. However, if there's limited genetic diversity, the chances of you reproducing with another organism that also has a faulty copy of that gene is much, much higher, so we may see the prevalence of that disease increase. This issue of genetic diversity as it relates to biodiversity also explains a few phenomenon that we see as part of our daily lives. For example, there's the founder effect. This occurs when a small subset of individuals moves to a new area. One of the most famous examples is the six-toed cats. For reference, cats are much like us, where they have five digits on each hand or paw. Polydactyly is a genetic mutation that causes someone to have extra digits. At some point, a cat with polydactyly, meaning it had extra fingers, made it to Key West. Key West is an island that's part of an island chain off the coast of Florida known as the Florida Keys. This cat made it to this island and went on to reproduce and now if you visit Key West, Florida today, you'll note that there's a very high number of six-toed cats on the island. There are also many cultural prohibitions against incest, which is reproducing with a close family member. Since we are so genetically similar to our families, reproducing with one another is more likely to result in disease. You're more likely to get two bad copies of a gene, for example. An interesting evolutionary and developmental quirk is that one of the reasons why adolescents start spending more time with their peers than their family around the same time as they reach reproductive maturity is because it increases the likelihood of reproducing with a genetically dissimilar individual. Rare genetic diseases are also more predominant in certain groups where either cultural or religious reasons prevent individuals from marrying outside of their group. These groups gradually become more genetically similar to one another over time, and these diseases can begin to emerge. The founder effect can also be at play here. For example, when a small group of people leaves an area, maybe they are leaving due to religious persecution and forming an exclusive colony somewhere else. Genetic diversity is related to extinction, another concept that we talked about in this module. Remember, extinction is the opposite of speciation, the total loss of one's species. Although extinction is a very normal biological process, some scientists believe that given how high the extinction rates are currently, that we're actually in the midst of the sixth mass extinction. Sometimes there can also be so few individuals of a animal species remaining that in spite of our best effort, extinction may be inevitable because there isn't genetic diversity among the remaining members. For example, cheetah numbers are very low and their genetic diversity is also quite low, which raises questions about their continued existence in spite of captive breeding programs. Why should we care about extinction and the preservation of biodiversity? Someone argued from a moral viewpoint that we have a collective obligation to take care of our home, both for ourselves, future generations, and for other life on the planet. From a medical viewpoint, pharmaceutical bio-prospecting or looking for novel medically relevant chemicals in nature can provide new medicines. Some plant-based medicines have been used for thousands of years, such as salicylic acid, which comes from willow tree bark. You may know it by its common name in the stores, aspirin. If deforestation in the Amazon continues, what other potentially therapeutic compounds will we miss? As we'll talk about in the rest of this course, we're also inherently interconnected with other organisms. What we as humans choose to do can have massive repercussions on the environment for the good or the bad. How are we connected to other life? Let's explore in the next module, ecology.
