Darwin, Lamarck, and Neo-Darwinism: Evolution Theories
Darwin’s Theory of Evolution
Darwin’s theory posits that populations evolve over time through a process of natural selection. Key points include:
- Organisms produce more offspring than can survive.
- Despite overpopulation, population sizes generally remain constant.
- This leads to a struggle for resources (food, space).
- Individuals within a species vary in their traits (some are more “fit”).
- The fittest individuals are more likely to survive and reproduce.
Conclusions of Darwin’s Theory
- Individuals with traits best suited to their environment have a higher chance of survival and reproduction, passing on those traits.
- Natural selection is a gradual process acting on populations, not drastically on individuals.
- Reproductive success, not necessarily overall “best” fitness, drives survival.
- Selection acts on phenotypic variability (heritable traits). Traits that reduce viability and reproduction are less likely to be passed on.
- The inheritance of small, advantageous variations selected by the environment drives continuous evolution.
Lamarck’s Theory of Evolution
Lamarck’s theory, now largely discredited, proposed that species change their bodies according to their needs, and their offspring inherit these acquired characteristics. Experiments, such as cutting the tails of lab rats, showed that acquired traits are not inherited, contradicting Lamarck’s theory.
Lamarck proposed that current species are the result of a long process of change experienced by all living beings.
Example: Giraffe’s Neck
Lamarck’s theory is often illustrated with the example of giraffes:
- Giraffe ancestors were similar to antelopes.
- Some individuals stretched their necks and front legs to reach higher leaves.
- These stretched body parts lengthened during their lifetime.
- These acquired characteristics were passed on to their descendants.
- Over many generations, this resulted in the long neck and forelimbs of modern giraffes.
This theory is based on the modification of organs due to intensive use, with these new features being inherited (inheritance of acquired characteristics).
Neo-Darwinism
Neo-Darwinism integrates Darwinian evolution with modern genetics and other fields. It explains how changes occur in offspring and are transmitted across generations.
Do Species Change?
Yes, comparing characteristics of living organisms with fossils reveals that some species have changed. For example, there are differences between humans who lived 200,000 years ago and modern humans.
Uniformitarianism (Charles Lyell)
Charles Lyell (1797-1875), an English geologist, proposed the theory of uniformitarianism. This theory states that the geological agents that shaped the Earth’s crust slowly and gradually in the past are the same as those acting today (wind, water, volcanic activity, etc.).
This theory suggests that the Earth is very old and that slow, gradual processes over long periods can cause major changes in the Earth’s crust. These concepts, contrasting with theories of catastrophic change, paved the way for evolutionary theories.