Natural selection drives adaptive evolution by selecting for and increasing the occurrence of beneficial traits in a population.
Natural selection only acts on the population’s heritable traits: selecting for beneficial alleles and, thus, increasing their frequency in the population, while selecting against deleterious alleles and, thereby, decreasing their frequency. This process is known as adaptive evolution. Natural selection does not act on individual alleles, however, but on entire organisms. An individual may carry a very beneficial genotype with a resulting phenotype that, for example, increases the ability to reproduce ( fecundity ), but if that same individual also carries an allele that results in a fatal childhood disease, that fecundity phenotype will not be passed on to the next generation because the individual will not live to reach reproductive age. Natural selection acts at the level of the individual; it selects for individuals with greater contributions to the gene pool of the next generation, known as an organism’s evolutionary fitness (or Darwinian fitness).  Fitness is often quantifiable and is measured by scientists in the field. However, it is not the absolute fitness of an individual that counts, but rather how it compares to the other organisms in the population. This concept, called relative fitness, allows researchers to determine which individuals are contributing additional offspring to the next generation and, thus, how the population might evolve. There are several ways selection can affect population variation:
As natural selection influences the allele frequencies in a population, individuals can either become more or less genetically similar and the phenotypes displayed can become more similar or more disparate. In the end, natural selection cannot produce perfect organisms from scratch, it can only generate populations that are better adapted to survive and successfully reproduce in their environments through the aforementioned selections. Galápagos with David Attenborough: Two hundred years after Charles Darwin set foot on the shores of the Galápagos Islands, David Attenborough travels to this wild and mysterious archipelago. Amongst the flora and fauna of these enchanted volcanic islands, Darwin formulated his groundbreaking theories on evolution. Journey with Attenborough to explore how life on the islands has continued to evolve in biological isolation, and how the ever-changing volcanic landscape has given birth to species and sub-species that exist nowhere else in the world.
Biological fitness is defined as __________. Possible Answers:
the amount of energy an organism can use in the environment
the average life span of an organism
the ability of an organism to survive and reproduce
the percentage of energy that is dedicated to mating
Correct answer: the ability of an organism to survive and reproduce Explanation: The biological fitness of an organism is dependent on its ability to survive and reproduce in a given environment. If different traits or alleles increase the fitness of an organism, those alleles will consequently increase in the gene pool, and that trait will increase in the population. This is how natural selection affects a population. There is inherent trade-off in biological fitness. A trait that increases ability to survive, but makes an individual sterile, decreases fitness because the organism cannot produce offspring to carry on the trait. Similarly, if a trait increases the ability to reproduce, but makes it harder to the organism to survive, it may die before being able to produce offspring. Both survival and reproduction are essential to defining the fitness of an organism.
Which of the following best describes biological fitness? Possible Answers:
Ability to compete against other organisms
Ability to grow to the largest size
Ability to reason and think logically
Ability to have superior physical strength
Correct answer: Ability to reproduce Explanation: Biological fitness in the evolutionary sense is only related to fitness in terms to reproduction. Because the primary goal of all organisms is to reproduce, or to pass their DNA onto offspring, fitness is defined as the ability to reproduce and create viable offspring. "Favorable" traits, such as intelligence, size, or strength, may increase the ability of an individual to survive and reproduce, thus increasing biological fitness, but cannot be used to directly define the fitness of the individual.
Darwinian fitness is a measure of __________. Possible Answers:
the ability of an organism to create offspring
the ability of an organism to kill another organism
the ability of an organism to use tools
the ability of an organism to protect its young
the ability of an organism to run for long periods of time
Correct answer: the ability of an organism to create offspring Explanation: The term "fitness" in evolutionary biology means the ability of an organism to pass on its genetic material to its offspring. Biological or "Darwinian" fitness is being able to live long enough to reproduce and keep the population or species alive. Most students confuse biological fitness with physical fitness because that is the context most often associated with the word.
In the study of evolution, sometimes it is useful to assess the biological fitness of an individual. What is the best criterion to use to measure the biological fitness of a certain large, strong iguana? Possible Answers:
The number of predators the iguana has in its environment
The number of the iguana's offspring who also survive to reproduce
The hunting ability of the iguana
Correct answer: The number of the iguana's offspring who also survive to reproduce Explanation: Biological or Darwinian fitness is defined based on the specimen's ability to reproduce and generate viable offspring. Essentially, the fitness of the individual is based on its ability to pass genetic information on to the next generation, as opposed to any physical characteristic or trait. Measuring the number of offspring who contribute to the gene pool is the best way to determine how genetically fit the iguana is. No matter how strong, large, old, or free of predation an animal is, if it cannot reproduce, it is not considered fit.
Which of the following is an example of an evolutionary advantage? Possible Answers:
A white rabbit that lives in a snow covered environment
A black moth that lives near an industrial site that produces a lot of soot
A cheetah that can run faster than the rest of his pack
A bird with a beak that can crack nuts in an environment where nuts are the main food source
Correct answer: All of these Explanation: All of the examples given provide an evolutionary advantage. A white rabbit in a snow covered environment has camouflage, which protects it from its predators. The same is true with the black moth living in a in a soot-covered industrial area. A cheeta that can run fastest has the greatest chance of catching prey and feeding himself/herself and his/her offspring. The same is true for a bird that can crack nuts in an area where nuts are the main source of food.
A female cheetah in Africa has four litters of cubs over her lifetime. Her first litter has six cubs that grow to adulthood and is fathered by the most spotted male in the area. Her second litter has four cubs that grow to adulthood and is fathered by the fastest male in the area. Her third litter has two cubs that survive to adulthood and is fathered by the strongest male in the area. Her fourth litter has five cubs that survive to adulthood and is fathered by the smartest male in the area. Which male cheetah has the most biological fitness? Possible Answers:
Can't tell from the given information
Correct answer: The most spotted male Explanation: The term biological fitness refers to reproductive success and is different than physical fitness. Since the most spotted male fathered the most cubs that survived to adulthood to reproduce themselves, he would be considered the most biologically fit. It is also important to note the inclusion of the "survived to adulthood" aspect since reproductive success is dependent on an organism's offspring being able to reproduce and contribute to the gene pool as well. For example, if the most spotted male had fathered a litter that initially had nine cubs, but only one of them survived to adulthood to have cubs of its own, he would no longer be considered the most biologically fit.
Cherub
SUNY at Binghamton, Bachelors, Biological Science. University at Buffalo, Current Grad Student, Medicine.
Kelie
Loyola University-Chicago, Bachelor of Science, Forensic Science.
Tierra
Norfolk State University, Bachelor of Science, Biology, General. UDC/Georgetown University, Master of Science, Cancer Biology...
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What determines the evolutionary fitness of an individual?
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