Arc 1: Midterm Prep Anthropology

What were the pre-Darwinian assumptions?

Pre-Darwinian assumptions included several key beliefs. First, species were thought to be created by a divine being, which meant they were seen as unchanging (creationism and fixity of species). The Earth was considered to be only a few thousand years old, giving little time for change (young Earth). The idea of the Great Chain of Being placed humans at the top of a fixed hierarchy of life. Nature was seen as having a grand design, meaning each species had a purpose. Typological thinking assumed species had a perfect, unchanging essence, with any variation considered an error.

Who were the people that influenced Darwin, and what ideas did they introduce?

Several people influenced Darwin’s thinking. Buffon proposed that the environment and geography cause variation in species. Erasmus Darwin, Darwin’s grandfather, introduced the idea that species might change over time. Lamarck proposed that traits acquired during an organism’s lifetime could be passed on to offspring, an idea known as the inheritance of acquired characteristics. Cuvier introduced catastrophism, suggesting that sudden disasters cause species extinction. Lyell’s idea of uniformitarianism argued that the Earth’s features resulted from slow, continuous processes, shaping Darwin’s thinking about gradual change. Malthus contributed the idea that populations grow faster than resources, leading to a struggle for survival, which became central to Darwin’s concept of natural selection.

3. Who was Alfred Russel Wallace, and what did he contribute to evolution?

Alfred Russel Wallace independently developed the theory of natural selection at the same time as Darwin. His work on biogeography and species in the Malay Archipelago influenced the understanding of how species form in isolated environments. Wallace’s manuscript, sent to Darwin in 1858, led Darwin to publish his own work on natural selection. Wallace is considered a co-discoverer of the theory, and his insights helped refine Darwin’s ideas.

4. What were the assumptions after Darwin?

After Darwin, assumptions about the natural world shifted dramatically. The idea of the Great Chain of Being was discarded, and humans were recognized as part of the natural world, subject to the same forces as other species. Creationism and the idea of a grand designer were replaced by evolutionary forces, particularly natural selection, as the drivers of change. The fixity of species was abandoned in favor of the idea that species evolve over time. Populational thinking became important, emphasizing that variation within populations is essential for evolution, with no fixed essence for any species.

5. Why is it said that Darwin is just a midpoint in the revolution?

Darwin’s work laid the foundation for evolutionary theory, particularly through his concept of natural selection. However, Darwin lacked a mechanism for inheritance, which wasn’t fully understood until the rediscovery of Mendel’s work on genetics. Darwin’s ideas were built upon by later scientists, leading to the modern synthesis, which integrated genetics with evolution, making Darwin’s work a crucial midpoint in the broader scientific revolution.

6. What is evolution?

Evolution is the process through which the genetic composition of a population changes over time due to mechanisms such as mutation, natural selection, genetic drift, and gene flow.

7. What is the unit of evolution?

The unit of evolution is the population because it is within populations that genetic variation exists and evolves over generations. Evolution acts on the gene pool of a population rather than on individuals.

8. What is a population?

A population is a group of individuals of the same species that live in a specific geographic area and are likely to interbreed. Populations share a gene pool, and evolutionary changes occur within this pool.

9. Name the different evolutionary forces and define each.

There are four main evolutionary forces: mutation, migration (gene flow), genetic drift, and natural selection. Mutation refers to random changes in DNA that create new genetic variation. Migration involves the movement of genes between populations, introducing new alleles into a population. Genetic drift refers to random fluctuations in allele frequencies, especially in small populations, where chance plays a significant role. Natural selection is the systematic process through which traits that improve survival or reproduction become more common in a population over time.

10. What are the effects, optimal population size, and impact on variation within and between populations for each evolutionary force?

Mutation is a random force that increases variation within and between populations, with no optimal population size for its effects. Migration is systematic and increases variation within populations while reducing it between populations, with larger populations better suited to its effects. Genetic drift is random, decreasing variation within populations and increasing it between populations, with small populations experiencing its effects most strongly. Natural selection is systematic, reducing variation within populations and increasing differences between them, and operates optimally in medium to large populations.

11. What are the types of selection, and what does each mean?

There are three main types of selection. Balancing selection favors the intermediate traits within a population, maintaining genetic diversity. Directional selection favors one extreme of a trait, shifting the population towards that extreme over time. Diversifying selection favors both extremes of a trait, which can increase variation within a population and may lead to the emergence of distinct subgroups or even speciation.

12. Why is the individual considered the unit of selection? And what is its challenge?

The individual is considered the unit of selection because natural selection acts on the traits of individuals, affecting their survival and reproductive success. However, the idea of group selection suggests that selection can also act at the level of groups, meaning that groups of individuals with certain cooperative or beneficial traits may have an advantage over other groups. This challenges the individual-centered view by proposing that traits beneficial for the group’s survival might sometimes be selected even if they don’t directly benefit the individual.

13. What evolutionary force played a role in most people having wet earwax?

Natural selection likely played a role in the prevalence of wet earwax in populations from humid climates, where it provided benefits like keeping ear canals clean and preventing infections. In this case, balancing selection favored wet earwax over dry earwax in specific environments, with medium to large populations being most affected. Natural selection systematically reduced variation within populations in regions where wet earwax was advantageous but increased differences between populations, such as those in dry versus humid climates.

14. What is the difference between microevolution and macroevolution?

Microevolution refers to small-scale evolutionary changes within populations, such as changes in allele frequencies over short periods. Macroevolution involves large-scale changes that lead to the formation of new species or higher taxonomic groups, occurring over much longer timescales.

15. What is the modern synthesis?

The modern synthesis is a framework that combines Darwinian evolution with Mendelian genetics, explaining how evolution operates through gradual changes in genetic variation within populations over time. It emphasizes the role of natural selection as the main force of evolutionary change while incorporating genetic principles.

16. What are the main components of the modern synthesis?

The modern synthesis is built on several key components: gradualism, which states that evolution occurs through small, incremental changes; the idea that natural selection is the most important evolutionary force; and the understanding that macroevolution is simply an accumulation of microevolutionary changes. It views evolution as opportunistic, irreversible, and not directed toward any particular goal. Natural selection shapes traits that increase reproductive success, and evolution occurs at the level of populations, not individuals.

17. What are the different types of genetic drift?

There are three types of genetic drift: founder effect, bottleneck effect, and sampling error. The founder effect occurs when a small group establishes a new population, leading to reduced genetic variation. The bottleneck effect happens when a population sharply decreases in size, leaving a small group with less genetic diversity. Sampling error occurs in small populations when traits are favored by chance, causing the sample to randomly favor one side of the bell curve instead of following the expected distribution, like having all daughters instead of an equal mix of sons and daughters in a small family.

18. What is the biological species concept, and how does it define a species?

The biological species concept defines a species as a group of organisms that can interbreed and produce fertile offspring in natural conditions. Members of the same species are reproductively isolated from other groups, meaning they do not naturally breed with individuals from other species.

19. What is the view of a species from a populational point of view?

Populations that don’t reproduce with other populations

20. What are the different modes of speciation? Describe each, and how does it occur?

There are three main modes of speciation: allopatric, parapatric, and sympatric. Allopatric speciation occurs when a population is geographically separated, leading to the evolution of new species due to isolation. Parapatric speciation happens when populations are partially separated and diverge into new species, often along a gradient or in response to environmental differences. Sympatric speciation occurs within a single population without geographical separation, usually due to behavioral or ecological differences that create reproductive isolation. A simple example of sympatric speciation is found in apple maggot flies, where some individuals adapted to breeding on apple trees while others continued breeding on hawthorn trees, creating reproductive isolation within the same area.

There has to be a selective pressure invovled.

21. What are reproductive isolating mechanisms (RIMs), and what types are there?

Reproductive isolating mechanisms are biological barriers that prevent species from interbreeding. There are two main types: pre-mating RIMs (barriers that prevent mating from occurring) and post-mating RIMs (barriers that occur after mating, preventing successful reproduction). Pre-mating RIMs include factors like behavioral differences, while post-mating RIMs include factors like hybrid sterility.

22. What are the different types of pre-mating RIMs, and describe each?

Pre-mating RIMs include habitat isolation (species live in different environments), seasonal isolation (species breed at different times), behavioral isolation (differences in courtship behavior), and mechanical isolation (differences in reproductive anatomy that prevent mating).

23. What are the different types of post-mating RIMs, and describe each?

Post-mating reproductive isolating mechanisms include gamete mortality, where sperm and egg cells fail to fuse, and zygote mortality, where the fertilized egg dies. Hybrid mortality refers to cases where hybrid offspring die before reaching reproductive age. Hybrid sterility means that hybrid offspring are sterile and unable to reproduce, which can be either complete (no reproductive ability) or partial (reduced fertility but not completely sterile).

22. What are the three different results of speciation?

The three outcomes of speciation include the development of generalized versus specialized forms, the emergence of homologous or analogous traits, and different patterns of evolutionary change, such as adaptive radiation, divergent, or convergent evolution.

25. What two types of forms are there from speciation? Describe each.

There are generalized forms and specialized forms. Generalized forms have broad adaptations that allow them to survive in a variety of environments, while specialized forms have specific adaptations that make them highly suited to a particular niche.

26. What two types of similar traits can happen? Describe each.

The two types of similar traits are homologous traits and analogous traits. Homologous traits arise from a common ancestor and are structurally similar despite different functions (e.g., human arm and bat wing). Analogous traits arise from convergent evolution and serve similar functions despite different evolutionary origins (e.g., bird wings and insect wings).

27. What are the different patterns of evolutionary change? Describe each.

There are four main types of evolutionary change: adaptive radiation (rapid diversification into multiple species to fill different ecological niches), divergent evolution (two species evolve in different directions from a common ancestor), convergent evolution (unrelated species develop similar traits due to similar environmental pressures), and parallel evolution (two related species evolve similar traits independently in similar environments).

28. What does adaptive radiation depend on, and why?

Adaptive radiation depends on two key factors: opportunity (such as the availability of unoccupied niches or the extinction of competitors) and adaptive potential (the ability of a species to exploit different resources or environments).

29. What is the difference and similarity between parallel evolution and convergent evolution?

Parallel evolution occurs when closely related species evolve similar traits due to similar environmental conditions, sharing a recent ancestor. Convergent evolution happens when distantly related species develop similar traits, often with a common ancestor in the distant past.

30. What were the characteristics of the modern synthesis or its view on evolution?

The modern synthesis views evolution as a gradual process driven mainly by natural selection. It integrates Mendelian genetics with Darwinian evolution, explaining how small genetic changes accumulate over time to result in larger evolutionary patterns. The process is seen as opportunistic, irreversible, and non-directed.

31. What does the modern synthesis think is the main force for evolutionary change?

The modern synthesis holds that natural selection is the most important force driving evolutionary change, shaping traits that improve survival and reproduction over time.

32. What challenges arose to the modern synthesis? Describe them.

Challenges to the modern synthesis include that the primate mover of evolution is mutation and not natural selection. The neutral theory of evolution states that some genes can be passed without giving any increase in fitness. Also, that some traits might not be adaptation but rather a byproduct. As well, that the tempo and mode of evolutionary change is through punctuated equilibria and cladogenesis rather than anagenesis and phyletic gradualism. As well, there is evodevo, non-genetic or soft inheritance and that the ecology and organisms can have an impact on their environment and in consequence the environment can shape them.

33. What is the critique of the adaptationist program?

Gould and Lewontin’s critique of the adaptationist program is that not all traits are adaptive. Some traits may be byproducts of other evolutionary processes, such as spandrels, which are architectural byproducts rather than intentional designs. They argue that some traits persist for reasons other than direct adaptation, and evolutionary biology should avoid assuming every feature has a specific adaptive purpose.

34. What are the tempo and modes of evolutionary change? Which tempo and mode is traditional, and which one is the alternative? Describe them.

The two tempos are phyletic gradualism (slow, continuous change) and punctuated equilibrium (rapid bursts of change followed by stasis). The modes are anagenesis, where one species gradually transforms into another without branching, and cladogenesis, where a species splits into two or more species. Gradualism aligns with anagenesis, while punctuated equilibrium aligns with cladogenesis.

35. Which of the tempo and modes is correct? Which one is more prevalent? Do they deny each other?

Both phyletic gradualism and punctuated equilibrium are valid, but gradualism is more prevalent in most evolutionary records. They do not deny each other; they represent different patterns of evolutionary change, with gradualism being more common but punctuated equilibrium explaining more rapid speciation events.

36. What could you imagine being present or observable in the fossil record when one or the other mode is present? Which mode is present?

When phyletic gradualism is present, we would expect to see a continuous, slow transition between species in the fossil record, with small changes accumulating over time. When punctuated equilibrium is present, the fossil record would show long periods of stasis with little to no change, followed by sudden, rapid appearances of new species. Depending on the situation, either mode could be observed, but gradualism is often more common, while punctuated equilibrium tends to explain more abrupt changes.

37. What is the traditional and alternate view of the relationship between microevolution and macroevolution?

The traditional view, aligned with gradualism, holds that macroevolution is simply an extension of microevolution, meaning large-scale changes are just an accumulation of small changes over time. The alternate view, supported by punctuated equilibrium, suggests that macroevolution involves more dramatic, sudden changes that are distinct from microevolution, meaning they are decoupled and should be studied separately.

38. What have been other recent challenges to the modern synthesis?

Recent challenges to the modern synthesis include Evo-Devo (evolutionary developmental biology), which focuses on how changes in developmental pathways and gene regulation during growth influence evolution. Soft inheritance or epigenetics introduces the idea that traits influenced by environmental factors (such as stress or nutrition) can be passed on to future generations without changes to DNA sequences. Lastly, the role of the environment in shaping evolution, through mechanisms like niche construction, suggests that organisms actively alter their environments, which in turn affects evolutionary pressures.

39. What is the difference between Evo-Devo and soft inheritance (epigenetics)?

Evo-Devo focuses on how changes in developmental genes during an individual’s growth can lead to large-scale evolutionary changes over time. It examines how slight mutations in regulatory genes can result in significant shifts in body plans or morphology. Soft inheritance or epigenetics, on the other hand, deals with how environmental factors can modify gene expression without changing the DNA sequence, and these changes can sometimes be passed on to the next generation. While Evo-Devo is concerned with genetic mechanisms over long evolutionary periods, epigenetics focuses on non-genetic, environmentally influenced changes that can affect multiple generations in the short term.

40. What is systematics?

Systematics is the branch of biology that focuses on the classification of organisms and their evolutionary relationships. It seeks to reconstruct evolutionary trees (phylogenies) to understand how species are related and how they have diverged over time. Systematics encompasses taxonomy, which is the naming and organizing of species, and phylogenetics, which studies evolutionary connections among species.

41. What is liminality and anomaly, and why are they important in classification systems?

Liminality refers to things that exist on the boundaries of categories, while anomalies are things that do not fit neatly into established classifications. Both are important in classification systems because they reveal the limitations and biases of the system being used. When a classification system encounters a liminal or anomalous case, it forces the classifier to either push it into an existing category or create a new one, highlighting how classification reflects more about the classifier than the classified object itself.

42. What are the taxonomy philosophies / schools, and describe them?

There are three key philosophies in evolutionary taxonomy: evolutionary taxonomy, phenetics, and cladistics. Evolutionary taxonomy groups organisms based on a combination of similarity and evolutionary history, considering both shared traits and the degree of divergence over time. Phenetics classifies organisms purely based on overall similarity, without considering evolutionary relationships. Cladistics, in contrast, groups organisms strictly based on shared derived traits and their most recent common ancestor, focusing on evolutionary history and ignoring the degree of divergence. The key difference between evolutionary taxonomy and cladistics is that evolutionary taxonomy allows for grouping based on both shared traits and evolutionary distance, while cladistics strictly classifies based on common ancestry and excludes consideration of similarity beyond that.

43. What is the difference between a grade and a clade?

A grade refers to a group of organisms that share a similar level of evolutionary development or a set of traits, but they may not all descend from a common ancestor. A clade is a group of organisms that includes a common ancestor and all its descendants, reflecting true evolutionary relationships. For example, reptiles are a grade, while mammals form a clade because they all share a common ancestor.