MICRO- EVOLUTION Evolution actually has two different types: macro- evolution and micro- evolution. Micro- evolution is what will be covered in this section. This type is changes within a single species, while macro- evolution is changes from one species to another species, but within a population. Both involve changes in a a gene pool, which holds all possible genes that will be passed on through offspring to the next generation. The gene pool also contains all different variations for all gene types. Micro- evolution has five ways of changing the gene pool: natural selection, gene flow, mutations, non- random mating, and genetic drift. We remember these as "The Five Fingers of Evolution." If you hold up your hand, each finger represents a mechanism, which are expanded below.
- GENETIC DRIFT This is represented by the pinky finger, as it is the smallest finger and symbolizes small population. Genetic drift is defined as a change in the gene pool because of random events. For example, as shown below, if you have a population of yellow, green, and red frogs and all the red frogs die off from a disease or environmental disaster, the gene pool for the next generation will be changed as the genes of the red frogs are lost. Therefore, the genetic diversity is decreased. This still occurs today, as genetic drift can occur at anytime, in any population, anywhere from a random event or change. Genetic drift has nothing to do with being the fittest; it is completely random and can occur anytime in an organism's life span. It happens within all populations, and there is no hiding from the affects of change.
- NON- RANDOM MATING Non- random mating is represented by the ring finger, as a ring symbolizes marriage. This is also known as sexual selection, which means organisms choose a mate based on criteria, such as their colour, territory, song, or size. There are two types of this; the first is harems, which menas all the females in a species choose a dominant male, such as in a lion population. In the case of lions, if the male dies, it is common for any offspring he had with the females to be killed by the next dominant male, as they don't have the DNA or genes of the new male. There is also assortative mating, which is known as an organism choosing a mate who looks like them, such as a human with blond hair choosing a mate who also has blond hair. Hence the name, species rarely ever mate randomly and most of the time mate based on criteria. One of the main examples of this is peacocks, as the female chooses a male mate based on the beauty of a male's feathers (shown below). Male crickets are also common to chirp songs in order to attract females, which can sometimes result in being eaten by a predator. We know this has occurred as when studying DNA sequences, we can see variations appear in populations. (Gregor Mendel justified this by studying pea genetics and showing by changing a genotype, you change the phenotype). Some of these may be a result of non- random mating, as the male and female genes get mixed up during crossing over and independent assortment.
- MUTATIONS Your middle finger symbolizes mutations; the M on your middle finger should remind you of this particular mechanism. A mutation is a change in a DNA sequence of an organism, and can be passed on through offspring to future generations. This can change the gene pool later on. Mutations are also not always bad; they can be either good or neutral as well, but a positive outcome from a mutation is extremely rare, because of all the "junk" and repeating DNA. An example of a bad one would be a mutation that gave and organism sickle cells, which clog capillaries and cut off circulation. The image below on the left shows a comparison between sickle cells and healthy red blood cells. On the other hand, a neutral mutation would be something like the Spirit Bear, which has a mutation in a pigmentation gene, turning its fur white. An ordinary bear of its species would be black, as the Spirit Bear is part of the American Black Bear, as shown in the photo below on the right. A beneficial mutation would be something like a mutation in an almond tree that prevents them from producing amygdalin, which has a bitter taste. Mutations still occur today in humans and other organisms, as changes in DNA sequences often happen randomly, or are inherited from previous ancestors. If it occurred before, it is sure to be passed on through generations today.
- GENE FLOW Gene flow is represented by your pointer finger, as it symbolizes movement. Gene flow itself is a transfer of a gene or allele from one population of a species to another population. This is done through either immigration or emigration. As a result, variations can be introduced into a population that have not been introduced before. However, if this gene flow stops or is somehow restricted, the populations who were formerly connected will now evolve and adapt on their own. For example, as shown below, if you have a population of green beetles and a population of tan beetles, and some of the tan beetles migrate into the population of green beetles, then the gene pool will be changed. The possible gene for a brown beetle is now in the population of green beetles, and if the two different types mate, their genes will be combined and their DNA will be passed on through future generations. We know this is still happening today as even humans mix genes when mating, as their DNA is not identical and their offspring is never a direct copy of the parents. Therefore, we know gene flow has occurred before since DNA has been mixed and passed on throughout our future generations.
- NATURAL SELECTION Your thumb is the final finger, and symbolizes natural selection. If you think of a thumbs up or a thumbs down, the thumbs up represents adaptations that are beneficial and organisms evolving well. The thumbs down, on the other hand, represents negative adaptations and organisms evolving poorly. Natural selection is also known as "Survival Of The Fittest", and is the mechanism of evolution. It basically means the organisms who can survive the best- who are the "fittest"- will adapt, survive, and mate, therefore producing fertile offspring and passing those genes onto the next generation. For example, as shown below, when a population of black and tan rock pocket mice live in a volcano rock environment, the tan mice will get eaten by the birds while the black mice will blend in against the rock. Through natural selection, the black mice are more fit and will therefore survive better and pass on their gene for black fur to the next generation. However, if they were living on a sand environment, the tan mice would be more fit and they would survive and pass on genes, while the black mice would not blend in and get eaten. We know this still occurs today, as when examining organisms in environments, we can notice how some live, survive, and pass on genes better than others will.