Evolution and Human Origins Flashcards

Evolutionary Adaptation

• Inconspicuous coloration of male guppies in pools with visual predators is an example of evolutionary adaptation.

Natural Selection

• Individuals best suited to their environment contribute the most genes to the next generation.
• Natural selection can only act on heritable traits.

Hardy-Weinberg Equilibrium

• Definition: a principle stating that the genetic variation in a population will remain constant from one generation to the next in the absence of disturbing factors.
• A population is at Hardy-Weinberg equilibrium for two alleles, A1 and A2. The frequency of the allele A2 is 0.3. What is the frequency of individuals that are heterozygous?
  • Given: frequency of A2 (q) = 0.3
  • Frequency of A1 (p) = 1 - q = 0.7
  • Heterozygous frequency = 2pq = 2 * 0.7 * 0.3 = 0.42
• The recessive allele b occurs with a frequency of 0.8 in a population of crabs that is in Hardy-Weinberg equilibrium. What is the frequency of individuals that are homozygous dominant (BB)?
  • Given: frequency of b (q) = 0.8
  • Frequency of B (p) = 1 - q = 0.2
  • Homozygous dominant frequency = p^2 = (0.2)^2 = 0.04
• Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 1 in 2,500 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?
  • Frequency of affected individuals (A2A2) = q^2 = 1/2500 = 0.0004
  • Frequency of A2 (q) = \sqrt{0.0004} = 0.02
  • Frequency of A1 (p) = 1 - q = 1 - 0.02 = 0.98

Hardy-Weinberg Conditions

• The easiest Hardy-Weinberg condition to meet in a lab setting with a small fish population is no gene flow.

Deviations from Hardy-Weinberg Equilibrium

• Deviations from the Hardy-Weinberg equilibrium occur when a population’s allele frequencies change over generations. Can indicate inbreeding, population stratification, and problems in genotyping.

Reproductive Isolation

• A gametic barrier is an example of a prezygotic isolating mechanism.
• One species of fish feeds in the muddy bottom of a lake. A second species eats insects that land on the water surface. This is an example of ecological isolation.

Artificial Selection

• Developing a strain of corn with lower fat content by choosing low-fat variants and crossbreeding them over several generations is an example of artificial selection.

Punctuated Equilibrium

• The punctuated equilibrium model is best illustrated by an example of adaptive radiation.

Vestigial Structures

• Boa constrictors have tiny pelvic girdles and leg bones inside their bodies. Because these structures are nonfunctional evolutionary baggage, they are called vestigial.

Evolutionary Fitness

• Having greater evolutionary fitness means being able to reproduce allowing them to pass their genes to the next generation.

Adaptation

• A mutation resulting in a heat-resistant enzyme in a bacterium living in a hot spring is the best example of an adaptation.

Sickle-Cell Allele

• Homozygotes with two sickle-cell alleles are selected against because of mortality. However, heterozygotes for sickle-cell allele experience few effects from sickle-cell allele and are more likely to survive malaria. In regions with malaria, the net effect of this exposure produced evolutionary change by increasing sickle-cell allele frequency.

Genetic Drift

• Genetic drift is due to chance events that change the allele frequencies in small populations.
• A population of endangered birds that includes only five individuals is most likely to experience genetic drift.
• Suppose a new mutation that improves metabolic efficiency is lost from a small population of mammals living in a region of seasonal food scarcity after a hurricane eliminates half the mammal population. This is an example of Genetic drift.

Gene Flow

• The net migration of alleles into or out of a population from neighboring populations is called gene flow.
• From an evolutionary point of view, gene flow occurs when a young male baboon leaves the troop that he was born in to join another troop.

Sexual Selection

• Male fish that display a bright blue color attract more mates as well as more predators. Maintaining that blue gene in the population is an example of sexual selection.

Mutations

• Mutations are important because they provide variation that can result in evolutionary change.

Phylogeny

• Butterflies and moths are more closely related to flies.
• Species X and Y share a greater number of homologous genes or features with each other than either does with species Z. This statement should be true, given that two extant elephant species (X and Y) are classified in the genus Loxodonta, and a third species (Z) is placed in the genus Elephas.
• Similarity due to common ancestry should be more common than similarity due to convergent evolution; this best describes the rationale for applying the principle of maximum parsimony in constructing phylogenetic trees.

Adaptive Radiation

• Adaptive radiation has occurred when a species invades a new habitat and evolves rapidly into several new species to better exploit new resources.

Allopatric Speciation

• Two species of squirrels live on either side of the Grand Canyon. It is believed that a long time ago, before being separated by the canyon, they were the same species. This is an example of allopatric speciation.

Founder Effect

• Parasitic Rhagoletis flies that show a preference for either hawthorn or apple trees (and are no longer interbreeding with populations found on the other host plant) illustrate the concept of founder effect.

Biological Species Concept

• The biological concept of species requires that organisms reproduce sexually.

Autopolyploidy

• The vegetable we know as the potato resulted from naturally occurring genome doubling within one species. In other words, the potato has twice as many chromosomes as the ancestor it was derived from. The potato could therefore be described as being the result of the process known as autopolyploidy.

Antibacterial Resistance

• Based on the way natural selection works, the best way to make use of antibacterial soap is to use it only when you need to be free of bacterial contamination, but not a lot, so bacteria will not evolve resistance to it.

Types of Selection

• Anolis lizards are placed on small islands with no large trees. In just a few generations, lizards in the population exhibit shorter hind legs than their ancestors. This is an example of directional selection.
• In one butterfly species, the colors of individuals range from white to black, with many shades of gray in between. If the butterflies in a mountain population become a similar shade of medium gray over the course of several generations, stabilizing selection is likely acting on the population.
• If the tallest and shortest individuals of a population of humans do not survive and reproduce as well as the individuals of average height, stabilizing selection would most likely result.

Genetic Variation

• A decline in genetic variation is the footprint that natural selection would most likely leave within the genomes of a population of organisms.

Human Genome

• Approximately 99% of genes in the human genome do not produce a final product.

Orthologous Genes

• The same gene in a different species is known as an orthologous gene.

Transposable Elements

• Selfish elements that replicate themselves and move around within a genome are known as transposable elements.

Hominins

• Hominins differ from all other known great apes in their bipedal posture.

Human Clade

• Humans do NOT belong to the clade Monotremes.

Human Evolution

• Certain populations of Homo sapiens evolved lighter skin (less melanin) to avoid vitamin D deficiency by increasing exposure to UV radiation more than 20,000 years ago, but less than 100,000 years ago.
• Adult humans from northern Europe are more likely to be able to digest milk than adult humans from Australia.

Melanin

• Tropical climates with abundant direct sunlight select for melanin, a human adaptation which helps to protect human skin from UV radiation damage.

Vitamin D

• Vitamin D is a nutrient required by pregnant human females for healthy fetal development and is degraded by sunlight exposure.

Lactose Intolerance

• Adult cows and goats are not naturally lactase persistent (False).
• Adult cats are lactose intolerant (True).
• On a global scale, most adult humans are lactose intolerant (True).
• Lactase persistent human populations are likely to have raised cattle for thousands of years (True).

Skin Color

• Human populations that have lived in coastal areas for many generations tend to have darker skin than inland populations at the same latitude (True).
• Vitamin D is a nutrient required for helping human bodies to use Calcium and is difficult to acquire in temperate climates with limited sun exposure.

Human Ancestors

• Homo erectus: My people are so widespread, anthropologists don’t agree on whether we belong to one species or two. We stood six feet tall and wandered the world for about a million years beginning close to two million years ago. My brain case is about 900 cc, twice as big as that of a chimp, but not quite as big as a modern human head.
• Homo naledi: My people lived in South Africa around 300,000 years ago. We are small in stature, with long arms and long fingers. Our skulls are small, but our faces are just about human.
• Homo neanderthalensis: My people trace their origins to a few hundred thousand years ago on the Eurasian continent. We were still there to witness the arrival of our sister species, Homo sapiens, when some of you came to Eurasia from Africa maybe 60,000 years ago. (We were shorter but stronger than modern humans, and our cranial capacity was, on average, slightly larger than yours.)
• Ardipithecus ramidus: I lived in an African forest more than four million years ago, where I walked upright but also climbed trees quite well with my specialized grasping foot. My brain case is about 450 cc, similar to a modern chimpanzee.
• Australopithecus afarensis: I lived more than three million years ago in Africa. I walked fully upright and my footprints a quite similar to those of modern humans. My brain case is about 450 cc, similar to a modern chimpanzee. My most famous fossil specimen is nicknamed Lucy.

Primates

• A primate has grasping hands and feet, forward facing eyes, large brains, & specialized dental patterns. Primates are Apes, humans, monkeys, lemurs, and tarsiers.
• Humans' closest living relatives are the chimpanzees and bonobos.

Human Origins

• The very earliest members of Homo sapiens would have been seen on the continent of Africa.

Mammal Subgroups

• The platypus and the echidna (spiny anteater) are the only modern mammals that lay eggs and belong to the subgroup Monotreme.
• Marsupials are the subgroup of mammals that raises their young in pouches.
• Humans belong to the subgroup of mammals called Eutherians.
• When modern humans arrived in Europe at least 40,000 years ago, they found this region already occupied by Neanderthals or Homo neanderthalensis.

Human Descent

• Direct descent of modern humans from Homo florensiensis is NOT supported by scientific evidence.

Ka/Ks Ratios

• Ka/Ks > 1 - Positive Selection
• Ka/Ks < 1 - Negative Selection
• Ka/Ks = 1 - Neutral Selection