Natural selection

Natural selection is one of the basic mechanisms of evolution, along with mutation,
migration, and genetic drift.

Darwin's grand idea of evolution by natural selection is relatively simple but often
misunderstood. To find out how it works, imagine a population of beetles

There is variation in traits.

For example, some beetles are green and some are brown.

There is differential reproduction.

Since the environment can't support unlimited population growth, not all individuals
get to reproduce to their full potential. In this example, green beetles tend to get
eaten by birds and survive to reproduce less often than brown beetles do.

There is heredity.
The surviving brown beetles have brown baby beetles because this trait has a genetic
basis.

End result:
The more advantageous trait, brown coloration, which allows the beetle to have more
offspring, becomes more common in the population. If this process continues,
eventually, all individuals in the population will be brown.
Gradualism and punctuated equilibrium are two ways in which the evolution of a species can
occur. A species can evolve by only one of these, or by both. Scientists think that species with a
shorter evolution evolved mostly by punctuated equilibrium, and those with a longer evolution
evolved mostly by gradualism.
Gradualism is selection and variation that happens more gradually. Over a short period of time it is
hard to notice. Small variations that fit an organism slightly better to its environment are selected
for: a few more individuals with more of the helpful trait survive, and a few more with less of the
helpful trait die. Very gradually, over a long time, the population changes. Change is slow,
constant, and consistent.
In punctuated equilibrium, change comes in spurts. There is a period of very little change, and
then one or a few huge changes occur, often through mutations in the genes of a few individuals.
Mutations are random changes in the DNA that are not inherited from the previous generation, but
are passed on to generations that follow. Though mutations are often harmful, the mutations that
result in punctuated equilibrium are very helpful to the individuals in their environments. Because
these mutations are so different and so helpful to the survival of those that have them, the
proportion of individuals in the population who have the mutation/trait and those who don't
changes a lot over a very short period of time. The species changes very rapidly over a few
generations, then settles down again to a period of little change.
This explanation talks about punctuated equilibrium as the result of one or a few mutations that
cause large change. However, punctuated equilibrium is any sudden, rapid change in a species
and can also be the result of other causes, such as huge and sudden changes in the environment
that result in more rapid changes in the organisms through harsher selection.
How did the tiger get its stripes: gradualism or punctuated equilibrium? We don't know whether the
tiger got its stripes through gradualism or punctuated equilibrium, but in order to explain both
concepts, here is how it could have happened through each. Let's assume that stripes are helpful
because they help the tiger to camouflage, blend in with the tall grasses where it lives, so that it
can sneak up on its prey (what it eats) and not be noticed.
Gradualism: A long time ago, there were a lot of tiger-like animals, but without stripes. Most of
them were unmarked, but a few had light markings and color variation in their fur. These few
blended in with the tall grasses a little bit better, so they were generally able to catch more food,
and fewer of the marked than unmarked ones died of hunger, so more of them were able to
reproduce. In the next generation, more animals were marked than in the previous generation. Of
those that were marked, some had more, some less, and some the same amount of marks than in
the previous generation. Also, the marks were more, less, or the same amount clearly defined.
Again, the ones with marks did better than the ones without, and the ones with more, clearly
defined marks did better than the ones with fewer or fainter marks. Very gradually, over many,
many generations, stripes over the tigers' whole bodies formed and appeared in the whole
population, because the tigers that survived in each generation were those whose marks were
most clear and contrasted most with the rest of the fur, and those that covered the most area on
the bodies of the tigers.
Punctuated equilibrium: A long time ago, there were a lot of tiger-like animals, but without stripes.
One time, a mutation occurred in a few of the animals, causing a huge change: they were born
with stripes! This was so helpful to survival that out of the whole population, none or almost none
of those with stripes died of hunger. They lived to reproduce, and their striped offspring also did
very well. Over only a few generations, the whole population was born striped.
A combination: Here is one idea of how tigers could have gotten their stripes by both gradualism
and punctuated equilibrium: A mutation had a huge affect, causing distinct, stripe-like markings.
These were then gradually "polished up" into stripes.
The idea of punctuated equilibrium originated long after the idea of gradualism. Darwin saw
evolution as being "steady, slow, and continuous". Later, scientists were studying fossils and they
found that some species have their evolution almost "mapped out" in fossils. For others they found
a few, very different species along the evolutionary course, but very few or no fossils of "in
between" organisms. Also, when dating the fossils, scientists saw that in some species change
was very slow, but in others, it must have occurred rapidly to be able to produce such change over
such a short amount of time. The scientists reasoned that there had to be another way that
evolution could have happened that was quicker and had fewer intermediate species, so the idea
of punctuated equilibrium was formed.

Creationism, the belief that the universe and the various forms of life were created
by God out of nothing (ex nihilo). It is a response to modern evolutionary theory,
which explains the emergence and diversity of life without recourse to the doctrine of
God or any other divine power. Mainstream scientists generally reject creationism.
Biblical creationists believe that the story told in Genesis of God’s six-day creation of
all things is literally correct. Others, such as old-Earth creationists, believe that a
creator made all that exists, but they may not hold that the Genesis story is a literal
history of that creation. Both types of creationists, however, believe that changes in
organisms may involve changes within a species (often understood as the “kind”
mentioned in Genesis 1:24) or downward changes such as negative mutations, but
they do not believe that any of these changes can lead to the evolution of a lower or
simpler species into a higher or more-complex species. Thus, the theory of
biological evolution is disputed by all creationists.

The French biologist Jean-Baptiste Lamarck (1744-1829) advocated the idea that
animals acquired characteristics after using certain physical traits constantly. He
believed, for instance, the reason why the necks of giraffes were long was because
they stretched to reach leaves on high trees. By the same token, the lack of a
human tail could be explained by the fact that humans did not use it.

The Lamarckian "use and disuse" idea is not necessarily convincing, however it
advanced evolutionary theory. When the English naturalist and geologist Charles
R. Darwin (1809-1882) published his theory of evolution by natural selection in
"On the Origin of Species," he continued to give credence to what he called "use
and disuse" inheritance, but abandoned other aspects of Lamarck's theories.

Despite this abandonment, interest in Lamarckism has continued as studies in

the field of epigenetic have highlighted the possible inheritance of behavioral
traits acquired by the previous generation.

Which one of Lamarckism or Darwinism is correct or not, or whether the

inheritance is congenital or acquired, it is a heated controversy whether our
mental and physical improvements are the result of adequate "use" of our
endowed gifts of living organs in our day-to-day life.

In general, organisms can selectively modify their bodies and mindsets through
the "use and disuse" of parts, and acquire or lose certain traits during their
lifetime. These modifications can be passed on to their offspring, as far as we
believe.

"Use" means to do what we can control while "disuse" signifies no longer in "use,"
becoming obsolete, referring to neglecting our given circumstances. If we use
some parts of our organs, they will keep those traits. If not, they will die out, no
doubt.

Claiming the environmental elements in our surroundings such as fresh air,

bright sunshine, pure water, green grass and close relations with our neighbors,
including nature, we have to let all our mental and physical "use" functions go
ahead for the future prosperity of our offspring, irrespective of age, sex, race and
color, on the global village, as medical doctors or professional therapists
recommend.

For applying the "use and disuse" theory to our daily routine, we have to learn
more about new emerging technology, exercise adequately for enforcing weak
physical points, and get together with other people quite often with diligence and
passion.

Having adequate daily eating and drinking habits, and sending continuous
impulses to our organs from our brains to our feet as necessary through moderate
exercise. In addition, we need to continue an optimistic but energetic drive
toward our plausible "use and disuse" life trails, to attain desirable inheritance to
our future-oriented outcomes to be anticipated for our offspring and future
generations.

As far as acquired characters are inheritable, the results of such inheritance are
cumulative from generation to generation, thus producing, in time, new species.
Acquired "use and disuse" characters are inherited and come out quite
differently, and the evolution can be inferred by action from the accepted
biological hypothesis. Lamarckian evolution in the context of epigenetic is
actually closer to the view held by Darwin rather than by Lamarck..
Human evolution, the process by which human beings developed
on Earth from now-extinct primates. Viewed zoologically, we humans
are Homo sapiens, a culture-bearing upright-walking species that lives on
the ground and very likely first evolved in Africa about 315,000 years ago.
We are now the only living members of what many zoologists refer to as the
human tribe, Hominini, but there is abundant fossil evidence to indicate that
we were preceded for millions of years by other hominins, such
as Ardipithecus, Australopithecus, and other species of Homo, and that our
species also lived for a time contemporaneously with at least one other
member of our genus, H. neanderthalensis (the Neanderthals). In addition,
we and our predecessors have always shared Earth with other apelike
primates, from the modern-day gorilla to the long-extinct Dryopithecus. That
we and the extinct hominins are somehow related and that we and the apes,
both living and extinct, are also somehow related is accepted by
anthropologists and biologists everywhere. Yet the exact nature of our
evolutionary relationships has been the subject of debate and investigation
since the great British naturalist Charles Darwin published his monumental
books On the Origin of Species (1859) and The Descent of Man (1871).
Darwin never claimed, as some of his Victorian contemporaries insisted he
had, that “man was descended from the apes,” and modern scientists would
view such a statement as a useless simplification—just as they would
dismiss any popular notions that a certain extinct species is the “missing
link” between humans and the apes. There is theoretically, however, a
common ancestor that existed millions of years ago. This ancestral species
does not constitute a “missing link” along a lineage but rather a node for
divergence into separate lineages. This ancient primate has not been
identified and may never be known with certainty, because fossil
relationships are unclear even within the human lineage, which is more
recent. In fact, the human “family tree” may be better described as a “family
bush,” within which it is impossible to connect a full chronological series of
species, leading to Homo sapiens, that experts can agree upon.