Macroevolution

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As you work through this set of chapter slides, keep in mind the notations that are included from your instructor. Open, read carefully, download if necessary, and use in conjunction with your reading and video lesson study. All these components supplement each other. The wise student will keep this in mind.

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Consider the following and keep it in mind:

a. Earth 4.5 billion years;

b. Life on earth appears around 3.5 billion years ago

c. Evolves from simple to compound to complex forms

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Genetic (allele) mutation & variation is the basis of all evolution. Without this evolution will not happen.

Nature influences the frequency of alleles in a population. Nature RESHUFFLES THE GENETIC DECK OF CARDS.

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Genotype + environment leads to phenotype or overall anatomical characteristics, both visible and invisible

Three types of natural selection to remember:

Directional selection = a move toward a particular feature, such as from a narrow to a broad beak in the Galapagos finches. Or vice versa!

Stabilizing selection--natural selection favors the center (e.g., large---->medium<----small); those individuals near the mean have a higher fertility rate.

Disruptive selection--natural selection favors both extremes; individuals near the mean have lower fertility rate. Small<--------->large; favors both ends of spectrum.

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a. Gene flow: New alleles are introduced to a population.

b. Genetic Drift: With “genetic drift”, by chance, all alleles in a population will NOT be represented proportionally in the next generation.

c. Founder Effect: A segment of a population migrates to another area (e.g., the AMISH) and may become the founding population for a later group that will result. Due to the very small genetic pool, down drastically from original larger pool, there is a tendency toward “bottlenecking.” No, silly, not hugging a bottle! What was originally a big pond of genetic possibilities is now a much narrower one. Guess what the danger is here? Check the book on it.

d. sexual selection leads to changes in gene frequencies from generation to generation. Individuals consciously choose mates: cute, wealthy, stable, smart, etc.

Types of nonrandom mating are CONSANGUINOUS mating, CROSS-COUSIN Preferential marriage, ASSORTATIVE mating.

Consanguineous mating (Inbreeding)

Cross-cousin preferential marriage -- you marry at the outer fringes of your available cousins. (See textbook on this one.)

Assortative mating: We pick from an assortment of possibilities out in the general population.

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Central to the scientific study of the diversity of life is the science of classifying organisms into different categories is known as taxonomy.

Linnaeus published the 10th edition of his classification of the living world in 1758. He developed or elaborated on the binomial system of genus & species

TERMINOLOGY: homology, analogy, convergent & parallel evolution

Anagenesis = evolution of a trait or a species in a “straight” line of development.

Cladogram (branching diagram showing evolutionary relationships) No time scales are involved.

Phylum. See Linnaeus’s Classification System: The hierarchy goes like this….

Kingdom-->Phylum-->Class-->Order-->Family-->Genus-->Species

[Look up “phenetics” and just be aware of its meaning.]

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*** WHAT IS A SPECIES? (p.92) It is “an interbreeding group of animals or plants that are reproductively isolated through anatomy, ecology, behavior, or geographical distribution from all other such groups.” (p.92) [Page numbers may vary; check your book.]

*** SPECIES CONCEPTS (see Box 5.1 p.93) Consider the difficulties with just how the species concept is applied.

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Refer to textbook here. This material is important to grasp as we move forward. See especially pp. 90-92.

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*** REPRODUCTIVE ISOLATING MECHANISMS: (see table 9.2 p.94) The elimination of gene flow between demes, usually the result of some type of geographical barrier, allows for the accumulation of different mutations within a deme. (p.105-6) See also next slide on all of this.

Reproductive isolating mechanisms may be external or internal:

A. External Factors: (all pre-mating) Ecological isolation, seasonal isolation, sexual isolation (can’t attract), mechanical isolation.

B. Internal Factors: Gametic mortality (sperm immobilized); zygotic mortality--developing egg “dies”

C. At or After Birth: (Post-mating) hybrid inviability (offspring die), and hybrid sterility.

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Read in conjunction with previous slide.

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*** HOW SPECIES ARE GENERATED OR FORMED:

Allopatric species arise due to geographical isolation (fig 5.11 p.95)

Parapatric species results when two populations or communities (of same species) live near or next to each other over a wide territory.

[See textbook for Anagenesis, Cladogenesis, and Sympatric Speciation.]

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*** TEMPO OF EVOLUTION: (p.96) There are two views of the usual tempo of evolutionary change:

Phyletic gradualism and Punctuated equilibrium.

Phyletic (phylum) gradualism: slow & gradual transformation. (Darwin’s view)

Punctuated gradualism/equilibrium: The normally gradual pace of evolutionary change is interrupted by shifts in tempo; evolutionary “bursts” occur.

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*** ADAPTATION (adaptive radiation) The movement of species into a new ecological niche. Four Factors are required:

1. No barriers

2. There is a variety of niches

3. The newcomers are pre-adapted

4. Either the new niche is unoccupied or the newcomers are able to compete successfully for resources.

* Extinction: (This is NOT an unusual event.)

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Adaptationism: The entire organism changes and not just one element or trait.

Reductionism (e.g., Gould p.97): only specific traits evolve.

Example: Is it just the Hummingbird’s beak or all of the Hummer that will adapt?

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“Evolution” A population is evolving IF the frequencies of its alleles are changing. No change, no evolution = Genetic equilibrium.

However, because the forces of evolution are always present, genetic equilibrium can only be “a hypothetical” state. Why have the H-W Equilibrium formula?

The Hardy-Weinberg formula allows us to measure the strength of evolutionary forces by making comparisons between the hypothetical situation of no change and change that is observed in real life situations. Godfrey Hardy and Wilhelm Weinberg developed the formula in 1908. And NO, you will not be expected to use it; just understand it’s reason for being.

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INCLUSIVE FITNESS: (p.100) The individual’s own fitness plus his or her effect on the fitness of any relative.

With kin selection, the individual contributes to his or her reproductive success either by:

1. Actually picking a partner, or

2. Acting in an altruistic manner that allows his or her kin to be reproductively successful. [Wolves in the wild; humans, too.]

The Coefficient of relatedness: The number of shared alleles decreases as our relationship becomes more and more removed from a common point of origin. Grandparents will differ markedly from their distant grandchildren (e.g., several generations removed the chance of like alleles being present will become less and less.)