Mechanics of Evolution

Mechanics of Evolution

Essential Content

A. Introduction to Other Mechanisms

1. Mechanisms of Evolution

a. Non-random mating

b. Genetic Drift (Bottleneck & Founder Effect)

c. Gene Flow – Migration

i. Immigration

ii. Emigration

2. Patterns of Macroevolution

a. Adaptive Radiation (Divergent evolution)

b. Convergent Evolution

c. Coevolution

3. Rates of Evolution

a. Gradualism

b. Punctuated Equilibrium

B. Trends in Human Evolution

1. Hominid Evolution: Early Ancestors (6 mya) to Modern Humans

a. Brain Size

b. Jaw Size / Facial slope

c. Language

d. Manufacture of Tools

C. Brain Structure

a. Cerebrum

b. Cerebellum

c. Brain Stem: Pons, Medulla Oblongata

d. Lobes: Frontal, Parietal, Occipital, Temporal

Objectives

• Analyze information to determine basic trends in hominid evolution

• Relate the development of language and the manufacturing of tools to changes in the skull and brain size in humans.

• Identify the major parts of the brain on diagrams.

• Analyze information to determine basic trends in hominid evolution

• Relate the development of language and the manufacturing of tools to changes in the skull and brain size in humans.

• Identify the major parts of the brain on diagrams.

Vocabulary:

speciation, hominid, cerebrum, cerebellum, ponds, medulla oblongata, frontal lobe, temporal lobe, occipital and parietal lobe, gene flow, gene pool, genetic drift, bottleneck, founder effect, artificial selection, adaptive radiation, coevolution, convergent evolution, gradualism, punctuated equilibrium

Evolution is the process by which modern organisms have descended from ancient ancestors. It is fundamental to the process is genetic variation upon which selective forces can act in order for evolution to occur.

So, how does it work?

• Descent and the genetic differences that are heritable and passed on to the next generation;

  • Evolution only occurs when there is a change in gene frequency within a population over time. These genetic differences are heritable and can be passed on to the next generation — which is what really matters in evolution: long term change.

• Mutation, migration (gene flow), genetic drift, and natural selection as mechanisms of change;

  • A mutation could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make genes for brown coloration more frequent in the population than they were before the mutation.

  • Gene Flow (think of it as a form of migration): Any movement of individuals, and/or the genetic material they carry, from one population to another. If gene versions are carried to a population where those gene versions previously did not exist, gene flow can be a very important source of genetic variation. For example some individuals from a population of brown beetles might have joined a population of green beetles. That would make genes for brown coloration more frequent in the green beetle population than they were before the brown beetles migrated into it.

  • Genetic drift: Imagine that in one generation, two brown beetles happened to have four offspring survive to reproduce. Several green beetles were killed when someone stepped on them and had no offspring. The next generation would have a few more brown beetles than the previous generation — but just by chance. These chance changes from generation to generation are known as genetic drift.

  • Natural selection: Imagine that green beetles are easier for birds to spot (and hence, eat). Brown beetles are a little more likely to survive to produce offspring. They pass their genes for brown coloration on to their offspring. So in the next generation, brown beetles are more common than in the previous generation.

• The importance of genetic variation; Without genetic variation, some of the basic mechanisms of evolutionary change cannot operate.

  • • • There are three primary sources of genetic variation, which we will learn more about:

        • 1. Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations. Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not "try" to supply what the organism "needs." In this respect, mutations are random — whether a particular mutation happens or not is unrelated to how useful that mutation would be. However, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and won't be passed onto offspring.

          2. Gene flow is any movement of genes from one population to another and is an important source of genetic variation.

          3. Sexual reproduction can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation. However, it can also break up "good" combinations of genes.

• The random nature of genetic drift and the effects of a reduction in genetic variation;

• variation, differential reproduction, and heredity result in evolution by natural selection; and

• Coevolution: describe cases where two (or more) species reciprocally affect each other's evolution. So for example, an evolutionary change in the morphology of a plant, might affect the morphology of an herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore...and so on.

Coevolution is likely to happen when different species have close ecological interactions with one another. These ecological relationships include:

• • • 1. Predator/prey and parasite/host

      2. Competitive species

      3. Mutualistic species

Study Guide