The
word evolution is derived from the Latin “evolver” meaning to roll forth. It is
defined as a gradual, orderly, and continuous process of change and development
from one condition or state to another. It encompasses all aspects of life,
including physical, psychologic, sociologic, cultural, and intellectual
development, and involves a progressive advancement from a simple to a more
complex form of state through the processes of modification, differentiation,
and growth.
In
genetics it is the theory of origin and propagation of all plant and animal
species, including humans, and their development from lower to more complex
forms through the natural selection of variants produced through genetic
mutations, hybridization, and inbreeding.
Natural
selection is the natural evolutionary processes by which those organisms best
suited for adaptation to the environment tend to survive and propagate the
species, where as those unfit are eliminated. On the contrary, the artificial
selection is the process by which the genotypes (the full set of chromosomes;
all the inheritance traits of organism) of successive plant and animal
generations are determined through controlled breeding.
Evolution
does not conform to an uniformitarian principle. When animals originated in a
bewilderingly fast and psychedelic 30-50 million years, was an event in which
evolution pushed itself to greater heights. The evolution of sight, of
burrowing, of active predation, all these innovations allowed animals to
explore evolutionary avenues that were until then closed off.
Evolution
is a cumulative process where each step builds on the previous steps. The best
evidence for evolution through natural selection is comparative molecular
biology. By comparing the genomes of all species, you can create an exact tree
of “cousinship” by literally counting the number of letters (of DNA) that they
have in common. The molecular evidence is overwhelming and the chimpanzee –
human resemblance is over 99 percent, however, all this has happened over a
long period of time.
The
genes affect the body in which they sit. The effect or the physical
manifestation of the genes on the body is known as phenotype. In other words,
the genes that sit in the body survive by virtue of making the body survive and
everything about a body is part of its phenotype. The phenotypes by which genes
survive don’t have to be in the body. For example, a bird’s nest is made by the
bird’s behavior but the nest is not part of the bird’s body and it is
considered an extended phenotype. Natural selection is working on the bird’s
genes to influence the phenotype of the bird to make a perfect nest.
Some
organisms can change their appearance, physiology and development in response
to changes in the environment. This is called phenotypic plasticity. Examples
are body builders in humans, water fleas that develop a spiny helmet in the
presence of predators or even the effect of learning on the brain – it’s a
ubiquitous phenomenon.
The
most phenotypically plastic organisms are plants. Unlike animals, plants are
evolved to be plastic in their physiology and development, with the best
example of this being heterophylly, the ability of many wetland plants to
change leaf structure and physiology in global warming, drought and in flood
conditions. (Hetero = different; Philly = related to leaf). Phenotypic
plasticity is one of the larger areas of current research from developmental
biology, ecology, and evolution.
The
evolution of genes, a system of heredity and information flow and storage,
fundamentally changed how evolution worked. The evolution of multicellularity
blew open the concept of individuality. The evolution in unicellular organisms
is radically different than in multicellular organisms. Similarly, the evolution of language and culture are representative of new domains for
evolution to grow into, where it will work in new ways.
Major
evolutionary transition is the coming together of individuals into a single
reproductive group: from genes to genome, genomes to cell, cells to
multicellular organisms to eusocial colony. Major evolutionary transitions
could also be defined by an increase in complexity. A multicellular eukaryote
is more complex than a unicellular bacterium. Some transitions are
characterized by new inheritance mechanisms - this unites the origin of life,
genes, and language. The discoveries of endosymbiosis and of widespread
horizontal gene transfer led to acceptance that evolution is no longer as
simple as gene frequency changes between populations.
When
developmental biology was brought into the picture it led to a major
evolutionary transitions paper in 1995. A new Synthesis that acknowledges and
explicitly includes all of these developments, has not yet been reached.
According to professor Richard Dawkins: “we understand the whole life but we
need to understand how that first step was taken – (how we got to) the first
self-replicating molecule. There are lots of theories and the truth probably
lies somewhere around the ones we’ve already got".
SOURCES
1.
McNamara, Alexander. A life in science – An interview with Prof. Richard
Dawkins. Focus Science and Technology, November 3, 2015
2.
Srour, Marc. Teaching Biology. Phenotypic Plasticity, May 2, 2013
3. Srour, Marc. Teaching Biology. Major Transitions in Evolution, November 7, 2015
