Lamarck Theory of Evolution —

Lamarck theory was the first mechanistic theory that was offered to explain Theory of evolution. Given by Jean Baptist Lamarck in 1809 in his book "Philosophie Zoologique".

He held that evolution is the result of constant striving by living beings to perfectly adapt to their existing environment.

Lamarck believed that organisms were not specially created but they have been shaped by the circumstances.

Underlying Concepts —

Though Lamarck himself proposes no postulates or law, all his discussion in the "Philosophie Zoologique" centered around four ideas these are — Growth, Pressure, Use & Disuse, Inheritance.

Theory of "Elan Vitae" or Growth.
Theory of Environmental Pressure, Needs and Spontanenous formation of organs.
Theory of use and Disuse
Theory of inheritance of acquired Charcaterts.

Detailed —

Every organism has a tendency to conitnually increase their size — Elan Vitae.
The growth in all living beings is due ot the action of internal life forces. — Elan Vitae.
Ex — a seed become tall tree, zygote becomes a giant creature.
The growth of a new organ and/or the modification of an oldern organ is need based. –– Formed due to environmental pressure, need. Ex —
Change in color in moth due to Industrial revolution in urban areas.
Lengthening of Giraffe's neck.
Degeneration of Kiwi's wing in New Zealand.
Use of an organ leads to its growth. But its non-usage for many generation leads to its degeneration
Lengthening of Giraffe's neck.
Degeneration of Kiwi's wing in New Zealand.
Development of web in between the digits in water birds to facilitate swimming.
Elongated body and loss of limbs in snakes due to continuous creeping through the holes and crevices.
All changes that take place in an individual's lifetime, by chance or by accident or by heredity, are passed down to subsequent generations. This is called the Principle of Inheritance of Acquired Characters.

Criticism —

It is non scientific as it is not based on or supported by facts.
It is not always true that evolution always leads to larger sized species, as evidence by extinction of dinosauras.
New Organs do not appear the way propsed by Lamarck –– Need theory –– Ex. Man Always wanted to fly, but this doesn't grow wings to human.
The third lamarckian principle emphasizes that the organs will develop due to use and degenerate due to disuse. the heart is not increasing its size in spite of its continuous use. The size and power of eyes are not increasing in the voracious readers with age.
Acquired characters cannot be inherited. Ex —
Foot binding in China — their children continue to have perfect legs.
Piercing of ears and nostrils in Indian women — still offspring do not show any trace of holes in ears and nostrils.

Significance —

It was the first mechanistic theory that offered the theory of evolution. Compare to earlier dark ages when influence of church was on peak.
His work paved the way for further research.

Read More

Define Cultural Relativism