MORPHOLOGICAL VARIATIONS

MORPHOLOGICAL VARIATIONS

from Femosky110 on 06/11/2020 01:20 PM

Morphological Variations In The Physical Appearance Of Individuals
Size, height and weight
Color (skin, eye, hair coat of animals
Finger prints
Variation in biology is all the differences which exist between members of the same species. It means any difference between cells, individual organisms, or groups of organisms of specific species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the appearance of the genetic potentials (phenotypic variation).

 

Variation may be exhibited in physical appearance, metabolism, fertility, method of reproduction, behaviour, learning and mental capability, and other observable or assessable characters.

Genotypic variations are caused by alterations in number or organization of chromosomes or by alterations in the genes carried by the chromosomes. The colour of the eye, body type, and ability to resist disease are genotypic variations.

Individuals with numerous sets of chromosomes are known as polyploidy. A lot of common plants have two or more times the normal number of chromosomes and fresh species may arise as a result of this type of variation.

A genotypic variation cannot be identified by observation of the organism; breeding experiments ought to be conducted under controlled environmental conditions to decide whether or not the alteration is inheritable.

In genetic variation, the genes of organisms within a particular population may change. Gene alleles determine different traits that can be transferred from parents to offspring.

Gene variation is crucial to the process of natural selection. The genetic variations that exist in a population occur by chance, but the progression of natural selection does not occur by chance.

Natural selection is the effect of the interactions that exist between genetic variations in a population and the environment. The environment establishes the type of variations that are likely to occur.

More favorable characters are in that manner transferred to the entire population

Genetic variation takes place majorly through DNA mutation , gene flow -movement of genes from one population to the other and sexual reproduction. Owing to the unstable nature of the environment, populations that are genetically unstable will be capable of adapting to altering situations more than those that do not possess genetic variation.

Environmentally resultant variations may arise as a result of a particular factor or the joint effects of many factors, like climate, food supply, and activities of other organisms. Phenotypic variations as well involve stages in an organism's life cycle and seasonal variations in an individual.

These variations do not include any hereditary changes and in general are not transmitted to future generations; as a result they are not important in the process of evolution.

There are two types of variation; continuous and discontinuous Variation.

Continuous variation is variation that has no boundary on the value that can take place within a population. A line graph is used to showcase continuous variation.

Some examples of continuous variation are variations in:
• height

• weight

• heart rate

• finger length

• leaf length

Discontinuous variation is variation that has distinct groups for organisms to belong to. A bar graph is normally used to showcase a discontinuous variation.

Some examples of discontinuous variation are:
• tongue rolling

• finger prints

• eye colour

• blood groups

A discontinuous variation with a lot of classes, none of which is extremely small, is referred to as a polymorphic variation.

The separation of the majority of higher organisms into males and females and the occurrence of different forms of a butterfly of the same species, each coloured to blend with varying vegetation, are examples of polymorphic variation.

Human Morphological Variation
Human variation arises from a number of factors which can be bluntly classified as either genetic or environmental implanted into the process of evolution.

Population genetics take care of variation within a single species or groups made up of the same species and in this case -Homo sapiens.

Population genetics framed in an evolutionary structure is known as microevolution while macroevolution is concerned with evolutionary procedures which lead to the formation of various species.

The fundamental features of human variability and how these are framed in genetic and adaptive terms.

A) Size, height and weight
Body size
Heritability estimates for the majority of body size measurements entail that about 80% of the variation in body size is as a result of genetic factors and about 20% is due to environmental factors.

Sexual variation in body size is typical of humans, with females being 90-95% the size of males in the majority of all populations.

Advantages of having a large body size
There are a few advantages attached to large body size. They include: People with large body size are:

• Stronger.

• Better predators - a lion for an example can kill a broad type of prey than a house cat.

• Larger bodied organisms have an added benefit in colder climates according to Bergman's rule which states that:

The larger the animal the better it is at retaining heat. This is the reason why during the glacial times a lot of lineages of animals developed giant types. Human being follows this rule in a great way.

People who occupy the poles have the tendency of becoming larger on the average than those living near the equator, but there are many exceptions.

Larger people are commonly faster runners. The fact that their stride length is longer and that they can apply more force with each stride due to larger muscles gives them this benefit.

Advantages of small body size
1. Small people need less food and can better survive when food is limited. Famines kill people in order of size starting from largest to the smallest.

2. Smaller people are usually faster and more agile. This is as a result of the principle of inertia from physics. A larger body needs more force to be in motion and more force to change direction than a smaller body.

Distribution of body size
1. Europeans possess the largest average body size. It is in Europe where Bergman's rule is majorly vividly applied. The largest Europeans are from the far north, and the people farther south of Europe are smaller.

2. Africans have both the world's tallest and the world's smallest people. The Nuer, Masai, Watusi, and related peoples of East Central Africa are the world's tallest and among the world's largest. The Pygmies of congo-West Central Africa and the Khoisan of Southern Africa are among the world's smallest.

3. Asians and Native Americans normally fall in the middle ranges. Just a few populations could be taken as large e.g- the Samoans.

Body weight
The majority of the variation in body weight of humans can be classified into linear build and lateral build.

The extreme linear build is found in the earlier mentioned tall peoples of East Central Africa. These people are very tall and slender. The chests, shoulders, and hips are extremely narrow - the narrowest in the world for their height. Their limbs are very long, particularly the legs.

On the other hand, the highly lateral build is found in a few Asian and

Native Americans cultures-the Eskimos, Japanese, Samoans, Apache, and many South American Indians exhibit lateral build. A few Caucasoid groups as well exhibit lateral build, particularly the peoples of northern Europe.

Laterally built people have the tendency to develop long and broad trunks, with wider chests, shoulders and hips. The widest hips of all can be seen among Europeans. Their limb bones tend to be short and the legs make less of a contribution to overall height.

Hair
A lot of things about hair are variable.

1. Hair Color:
Generally, dark hair goes with dark skin and light hair goes with light skin.

You can possess dark hair with light skin, but it is rare to possess light hair with dark skin. People can as well different color of hair on different parts of their body.

Blond hair has little melanin and black hair and in reality very dark

Brown has a lot of melanin. Skin melanins are always brown while hair melanin can be either brown or red. Generally, brown melanin is stronger in color than red melanin and can cover it.

The distribution of hair color is almost completely a European feature, with the majority of the rest of the world's people possessing dark brown hair.

The farther north in Europe the more likely the hair is to be blond. The farther west in Europe you go; the greater the tendency of the hair to be red.

2. Hair curvature
The degree of curvature of the hair can be divided into 3 categories: straight, wavy, and curly. The shape of the hair follicle determines the curvature of the hair. Round follicles give rise to straight hair, oval follicles give rise to wavy hair, and disk-shaped follicles give rise to curly hair.

Straight hair is seen all over the majority of world population, including the Americas, Asia, and parts of Europe. Europe has the greatest hair variation in hair curvature. It ranges from straight to very wavy. The Middle East and North Africa have a lot of wavy and a few curly heads.

Subsaharan Africans range from curly to very curly. The curliest hair is found in the Khoisans whose hair is often so tightly curled that it is called peppercorn hair because it looks like pepper corns placed on their heads.

3. Hair length:
A lot of people are amazed that there is as well genetic variation in hair length. Just like in other mammals, every one of us has a particular hair length outside which the hair plainly won't grow. Hair length is longest in people who have round follicles, for the fact that round follicles appear to hold the hair better.

Eyes:
Eye color and type show another remarkable range of variation. The colored part of the eye-the iris surrounds the pupil of the eye and possesses muscles which dilate and contract the pupil. The iris has a lot of layers; two among the layers contain melanin. All eye melanin is brown.

The variation in eye color is as a result of the pigmentation of the exterior layer of the iris. The iris may or may not be pigmented.

Ears:
Ears are very different in size, size of the ear lobe, protrusion, and whether the ear lobe is free or attached.

The African type of ear is a relatively small, non-protruding ear with small free lobes. The American and Indian type is the other extreme in average size and protrusion, and Asians typically have the maximum frequency of attached ear lobes. Europeans are the most variable and have ears that span the whole range of human variation.

Lips:
Possessing different types of lips is exceptionally a human characteristic. Every human being has lips, which differ basically in the extent to which they are rolled up to expose the pink membranous portion.

This observable fact is known as lip eversion. Everted lips appear to have a slight capacity to cool the body due to the fact that capillaries run very close to the surface of the lips, and the slight moistness of the lips assists to cool the body through evaporation.

The majority of everted lips are found on the faces of some Africans and the least everted lips on the faces of some Europeans.