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:

5. 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.

6. 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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10. • 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:

11. 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.

12. 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).

13. 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”.

14. “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

15. 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.

16. 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.

17. 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.

18. 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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