Evolution ( Macro and Micro Evolution).pptx

Human evolution

1. MACRO AND MICRO EVOLUTION

2. EVOLUTION: In biology, evolution is the change in heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Genetic variation tends to exist within any given population as a result of genetic mutation and recombination.Evolution occurs when evolutionary processes such as natural selection (including sexual selection) and genetic drift act on this variation, resulting in certain characteristics becoming more or less common within a population over successive generations.It is this process of evolution that has given rise to biodiversity at every level of biological organisation .

3. MICRO AND MACRO EVOLUTION:

4. Example of micro evolution: The size of the sparrow Sparrow populations in the north are larger-bodied than sparrow populations in the south. This divergence in populations is probably at least partly a result of natural selection: larger-bodied birds can often survive lower temperatures than smaller-bodied birds can. Colder weather in the north may select for larger-bodied birds.

5. Example of macro evolution Homo sapiens
Human macroevolution from our ape ancestors is indicated by fossil records. Examples of the fossils that support the theory of Homo sapiens macroevolution include Homo habilis , Homo rudolfensis and Homo erectus.

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7. Macroevolution usually means the evolution of large-scale structures and traits that go significantly beyond the intraspecific variation found in microevolution (including speciation).In other words, macroevolution is the evolution of taxa above the species level (genera, families, orders, etc.).
Macroevolution is often thought to require the evolution of completely new structures such as entirely new organs. However, fundamentally novel structures are not necessary for dramatic evolutionary change. For instance, the evolution of mammal diversity in the past 100 million years has not required any major innovation.All of this diversity can be explained by modification of existing organs. Macroevolution:

8. Macroevolutionary processes: Speciation vs macroevolution : Charles Darwin and his followers argued that speciation can be extrapolated so that species not only evolve into new species but also into new genera, families and other groups of animals. In other words, macroevolution is reducible to microevolution through selection of traits over long periods of time although some authorsclaimed that macroevolution is not reducible to microevolution.

9. Evolution of new organs and tissues: One of the main questions in evolutionary biology is how fundamentally new structures evolve, such as new organs. As can be seen in vertebrate evolution, most "new" organs are actually not new—they are still modifications of previously existing organs. Examples are wings (modified limbs), feathers (modified reptile scales),lungs (modified swim bladders, e.g. found in fish)or even the heart (a muscularized segment of a vein).

10. Molecular macroevolution: Microevolution is facilitated by mutations, the vast majority of which have no or very small effects on gene or protein function. For instance, the activity of an enzyme may be slightly changed or the stability of a protein slightly altered. However, occasionally mutations can dramatically change the structure and functions of protein. This may be called “molecular macroevolution”.

11. “ Macromutations ”: Single mutations leading to dramatic change: While the vast majority of mutations are inconsequential, some can have a dramatic effect on morphology or other features of an organism. One of the best studied cases of a single mutation that leads to massive structural change is the Ultrabithorax mutation in fruit flies. The mutation duplicates the wings of a fly to make it look like a dragonfly which represents a different order of insect

12. Microevolution: Microevolution is the change in allele frequencies that occurs over time within a population.This change is due to four different processes: mutation, selection (natural and artificial), gene flow and genetic drift. This change happens over a relatively short (in evolutionary terms) amount of time compared to the changes termed macroevolution.
Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution; for example, bacterial strains that have antibiotic resistance.

13. Mutation : Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation, viruses, transposons and mutagenic chemicals, as well as errors that occur during meiosis or DNA replication.Errors are introduced particularly often in the process of DNA replication, in the polymerization of the second strand. These errors can also be induced by the organism itself, by cellular processes such as hypermutation .

14. Selection : Selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations.
It is sometimes valuable to distinguish between naturally occurring selection, natural selection, and selection that is a manifestation of choices made by humans, artificial selection. This distinction is rather diffuse. Natural selection is nevertheless the dominant part of selection.

15. Genetic drift: Genetic drift is the change in the relative frequency in which a gene variant (allele) occurs in a population due to random sampling. That is, the alleles in the offspring in the population are a random sample of those in the parents. And chance has a role in determining whether a given individual survives and reproduces. A population’s allele frequency is the fraction or percentage of its gene copies compared to the total number of gene alleles that share a particular form.
Genetic drift is an evolutionary process which leads to changes in allele frequencies over time. It may cause gene variants to disappear completely, and thereby reduce genetic variability. In contrast to natural selection, which makes gene variants more common or less common depending on their reproductive success, the changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.

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