In this lecture, I will tell you what the theory of evolution is about. The theory that explains how life diversified into many incredible forms that we see nowadays. I will discuss how mutations are the raw material of evolution, and explain how natural selection works on these mutations, and results in accumulation of changes in these traits. The blue whale is the biggest animal on Earth. It can reach over 30 meters and weigh up to 100,000 kilograms. To grow to this staggering size, blue whales search for swarms of krill and other small animals in the oceans. When they open their jaws, two touring gars of sea water will enter. With one such swallow of water, a blue whale can gather half a million of calories. You will need to eat a thousand hamburgers. Blue whales are not only remarkable for their size and appetite. Although they have fish like bodies that are well-suited for swimming, staying underwater for an hour is fatal to them. Unlike fish that draw oxygen from water through their gills, blue whales must rise to the ocean's surface to take a breath. Another oddity is that instead of laying eggs, like fish, whales give birth to live young, and breastfeed their young for many years. While blue whales are the largest animal on earth, the smallest living things are viruses. They measure about a 100 nano meters across. About the 1000 times smaller than the width of human hair. And unlike animals, viruses are exquisitely simple. The virus that causes influenza, for example, has only ten genes. We, by contrast, have about 20,000 genes. Yet just because they are small and simple, doesn't mean that they are not extremely important. Viruses replicate by invading cells and hijack their molecules to assemble copies of themselves. And as they spread through their host, they cause a wide range of diseases, some mild and some devastating. Each year, for example, the human AID virus, kills almost 2 million people. Blue whales and viruses demonstrate the staggeringly different forms that life can take. They're in fact so different, that it can be hard to imagine that a single explanation can account for them both. Not to mention, all of the other living things that share planet Earth with them, and yet such an explanation does exist. Viruses and whales and all other living things are the products of evolution. The theory of evolution explains how living organisms develop and diversify over generations. Something to understand straight away, is that it doesn't explain the origin and development of the universe, nor does evolution exactly tell us how life began on Earth. But it helps us to understand, once life has become into extinction, how life diversified in the many incredible forms that we see now in the fossil record. It explains how new life forms emerge from earlier existing life forms. It helps us to make sense of modern organisms to continue to adapt and change today. Even if life on Earth started from outer space, this would not affect the evidence for evolution. It is also important to understand what a theory is. Outside science, a theory means a hunch or a unsupported personal feeling. Within science, a theory is a well-substantiated explanation accounting for a body of well-documented facts. So whenever we encounter statements like evolution is just a theory, not a fact, that whoever is making that statement is using the term incorrectly. So in biology, evolution can be defined as any change in the heritable or genetic traits by which populations of organisms change over time. These traits can be physical traits such as fur color of rabbits or spots on a butterfly wings or instinctive behaviors like dogs that take a friendly sniff off each other. These changes are observed as the changes of inherited traits in a population that occur from one generation to the next. So how exactly does evolution work, what is needed for evolution to occur? Let's start with some well known facts. We know that all organisms are capable of reproduction, they make children, they make copies of themselves. They do this by duplicating their DNA and passing this DNA on to the next generation. If it all goes well, the process of DNA duplication would result in offspring with identical DNA molecules as their parents. However, nature is not perfect. When DNA is copied, errors can occur, which modifies the DNA code. These errors are called mutations. Many people talking about mutations, refer to dramatic malformations. Animals with five legs, for example, or Pokemon, or more far-fetched that dogs can produce cats. In biology, mutations are simply changes in genetic variation with the population brought about by changes in the DNA sequence. Such as nucleotide substitutions, insertions, deletions or recombination. In biology, mutation can occur anywhere in the DNA molecules and mostly at random throughout the DNA and produce variation in traits that are encoded by debt portion of the DNA. But mutation is not the only cause of genetic variation, because it is not only the DNA that is important for the expression of traits. Other genetic studies, for example, show that genes can be switched on and off. This genetic inhibition or activation of genes can be inherited and can thus be expressed in later generations. So, the variation in heritable traits that we can observe in almost all populations is the result of mutations in the DNA of those organisms. And epigenetics, it make offspring look slightly different from their parents. Another fact, we also know that physical and behavioral traits of parent life forms are inherited by the next generation. And if through the process of artificial selection, many traits can be ejaculated in the later generations. This can be achieved fairly simple by crossing those individuals that exhibit those traits more strongly and to repeat this process for successive generations. Breeding horses with a good competition record will likely produce offspring that does well in competition also. And if we would be able to go back in time a few thousand years, you would find that all dogs originally evolved from wolf like and ancestral group of grey wolves. The evolution of dogs from generation to generation was guided by humans. Humans would have picked dogs that they liked and let them breed and only keep the puppies with the most desirable trait. When time went on, breeders selected for different features. Some selected for large sizes, some selected for small sizes. Some for brain and some for bren. Today, descendants of wolves have branched out in hundreds of breeds, very few will behave much like their ancestors. So the existence of small difference in heritable traits caused by mutation, will result in genetic variation in the breeding stock that breeders can select for. These small changes in the traits of a population over generations, can add up to dramatic changes over long time. So to get from a wolf to a dog, the breeder guided the genetic variation. But biologists say that an elephant evolved from a small shrew-like ancestor, and these are a lot more different than a dog from a wolf. So who was the breeder in that case? Who guided evolution here? In the mid 1800s, two men, Charles Darwin and Alfred Russell Wallace, independently discovered that the breeder is not necessarily be needed. There is another force capable of guiding random evolution to produce older and complex function of organisms. They called it natural selection. So if a grey hug breeder selects for the faster dogs for breeding his breeding stock and in the wild for the fastest gazelles which outrun the predator and survive to reproduce, then both the grey hug breeder and nature favor certain individuals for others to reproduce offspring and passing on their genetic variation to the next generation. Natural selection is nature's way of artificial human guided breeding. Like with artificial selections, variation in traits emerges as a result of mutation and reproductive opportunities are limited. Not because of human influence, but because of factors other than human influence. Reproductive opportunities are limited because individuals within populations are competing for limited resources, such as food, and space, or differ in the way they can avoid parasites and cope with diseases. Let's look at another example and look at a variation in core, for example, take this insect. If genetic variation in this beetle makes some of its offspring less conspicuous to predators, they'll have a greater chance of surviving and reproduction. And in the course of time then, the insects with this kind of variation may become more abundant within the population. If on the other hand a genetic variance makes the offspring more conspicuous to predators, they may not survive to reproduce and these variants are eliminated by natural selection. This trait and other traits have evolved in the natural world. And all traits serve some specific function and contribute towards different organisms reproductive success. And clearly, if organisms that exhibit many of these traits manage to reproduce, they perpetuate that genetic information including information for these traits in the next generation. So let's recap what we have discussed so far. We have defined biological evolution as any change in heritable trait within a population across many generation. Mutations are the raw material for evolution. Mutations occur in DNA each time DNA is being duplicated for replication. Mutations result in variation in heritable traits. It is a fact that not all organisms survive until reproduction. There is limited opportunity for reproduction. A natural selection is a mechanism that results in favoring individuals that have certain heritable traits that enable that individual to survive and to reproduce more successfully than others in a particular environment. In the next lecture, I'll introduce genetic drift as the second force in evolution in addition to natural selection. Discuss speciation and the evidence we have that evolution is a process of accumulation of small changes over time. In other words, evolution is descent with modification.
