Evolution and Speciation: A Comprehensive Overview
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The Stages of Evolution and Speciation
The evolution of changes in living things that occur over time, leading to new species, can be distinguished in four stages:
Production of Evolutionary Change
Natural selection favors certain individuals while harming others. Both still belong to the same species.
Genetic Isolation of the New Population
To constitute a new species, it's imperative that members of the new species do not reproduce with the originals. This occurs when the new settlement becomes genetically independent. Various types of barriers include:
Geographical Barriers
Prevent physical contact between populations (among individuals).
Sexual Barriers
Due to anatomical differences that prevent mating or lack of synchrony in the fertile period, reproduction is not possible even when individuals live in the same place.
Physiological Barriers
Inconsistencies in the functioning of sperm cells prevent fertilization, even if individuals can mate.
Chromosomal Barriers
Changes in the chromosomes prevent individuals from having offspring with the rest.
Ethological Barriers
New behaviors in certain individuals produce rejection by others, occurring during courtship.
Gradual Differentiation
The population changes due to accumulated new mutations and will differ little by little more than the original population.
Speciation
The anatomical, physiological, or genetic changes are so significant that it is not possible to obtain mixed descent. From there, the populations are considered two distinct species. Even if isolation barriers disappear, these species may not be able to reproduce.
The Hominid Family
The hominid family is characterized by being upright and bipedal.
Bipedalism may have arisen in some primate groups forced to leave their arboreal life because of climate change that occurred 15 million years ago in the African savanna. An upright position helped them to see prey and predators, improve vision, and free the hands, which could be used in activities.
The evolutionary acquisition of bipedalism was very important because it caused necessary changes to the skull for the upright position. The pelvic spine and the extremities varied in morphology and development, and the brain became more complex. True hominids appeared at the end of the Pliocene, 6.5 million years ago, under the name Australopithecus.
Genus Homo
The basic feature that sets the genus Homo apart is the ability to handle tools and instruments. This requires a hand with an opposable thumb that enables precise movements of the fingers and a brain sufficiently developed to send appropriate commands to the muscles involved.
The following species of the genus Homo can be noted chronologically:
- Homo habilis
- Homo erectus
- Homo sapiens