Evolution of Primates to Hominids: From Lamarck to Darwin and Beyond

Posted on Aug 12, 2024 in Biology

Transformer LAMARCK: Jean-Baptiste Lamarck’s theory of evolution, first explained in his 1809 book Philosophie Zoologique (Zoological Philosophy), attempted to explain how changes occurred within species and how new species arose. While not explaining the origin of all species, it was an important step that established the concept of evolution.

Summary of Lamarck’s Ideas:

  1. The simplest life forms often arise by spontaneous generation.
  2. All organisms have an internal momentum that leads them towards perfection and complexity, enabling them to overcome environmental challenges.
  3. The environment changes and creates new needs, forcing individuals to adapt by increased use of certain body parts while others fall into disuse.
  4. Alterations developed, acquired, or lost during an organism’s lifetime are maintained and transmitted to offspring. This explanation is known as Lamarck’s inheritance of acquired characteristics.

Analysis of Lamarck’s Proposals:

Lamarck proposed that an organism’s lifestyle influences its chances of survival and those of its descendants. Today, his mechanisms are rejected for the following reasons:

  1. He failed to demonstrate an impulse towards complexity in any living being.
  2. It is impossible to prove the inheritance of acquired characteristics. We now know that genes are inherited, not acquired traits.

Darwin’s and Wallace’s Natural Selection:

Both Alfred Russel Wallace and Charles Darwin independently arrived at the same conclusion about the mechanism of evolution. Darwin proposed his theory of evolution based on the following principles:

  1. In a changing world, organisms are also changing, exhibiting a wide variety of traits within wild populations. Some species become extinct, and new ones appear.
  2. The process of change is gradual and continuous.
  3. Organisms share similarities, indicating they are related.
  4. The mechanism driving these changes is natural selection.

Natural Selection According to Darwin:

  1. Populations of living things exhibit individual variations that differentiate them, despite belonging to the same species.
  2. These individual differences are heritable. There are two types of heritable differences: those conditioned by direct environmental action and spontaneous changes, such as the appearance of individuals with shorter legs, allowing them to adapt to their environment. This is known as adaptation.
  3. Despite the growth potential of populations, their numbers remain relatively constant. This led Darwin to question whether death was random. In response, he conceived the idea of the “struggle for existence” or survival.
  4. Conclusions: Real evolutionary change occurs when reproduction is considered. If the fittest individuals survive longer, they will reproduce more, and their offspring will inherit the characteristics that contributed to their success.

Neo-Darwinism or the Synthetic Theory:

In the 1940s, Neo-Darwinism, or the Synthetic Theory of Evolution, was established. It is called Neo-Darwinism because it revises Darwin’s theory of natural selection and synthesizes it with modern knowledge of the evolutionary process.

Overview of the Synthetic Theory:

  1. Variations are due to mutations that occur randomly among individuals in a population.
  2. Natural selection favors beneficial mutations, increasing their frequency and leading to adaptation.
  3. Evolutionary change is gradual and slow, driven by natural selection. This process is called speciation.

From Primate to Hominid:

Hominids are a group of primates whose origins trace back to Africa approximately 7 million years ago. Humans are hominids, but not all hominids are human beings; only those belonging to the genus Homo. Defining features of hominids include:

  1. Bipedalism: They move upright on two legs, which determines the position of the foramen magnum at the base of the skull, allowing for better support of the vertical weight. The spine has three curves, the pelvis is wider and shorter, the leg bones are longer, and the thumb on the limbs loses its opposability.
  2. U-shaped Palate: Their palate is U-shaped, with smaller teeth.
  3. Large Brain: Their skull houses a larger brain, which is related to a high-energy diet.

The First Hominids:

  1. Ardipithecus ramidus: The oldest known hominid. While exhibiting distinct anthropoid features, it is debated whether they had acquired functional bipedalism.
  2. Australopithecus anamensis: Had a simian appearance but possessed hominid characteristics like bipedalism and thick tooth enamel.
  3. Australopithecus afarensis: Had a protruding muzzle and a bony ridge along the skull’s axis. Its brain capacity was larger than that of chimpanzees.
  4. Hominids After A. afarensis: Showed two anatomical trends: a more gracile form, represented by A. africanus, and a more robust form, represented by Paranthropus.

Humanization: The First Humans:

Homo habilis:

The first Homo species for which remains have been found. They created primitive stone tools. Their skull was larger than that of the australopithecines, and their teeth were similar to ours. Homo habilis began to lose body hair and had a diet dominated by hard plant foods.

Homo ergaster:

Their skull was larger than that of H. habilis, with smaller teeth adapted to a meat-based diet. Their skeleton was similar to modern humans. H. ergaster is believed to be the first human species to leave Africa.

Homo erectus:

The remains of “Java Man” and “Peking Man” are classified as Homo erectus. This species arose around 1 million years ago and disappeared around 400,000 years ago. They used fire. Their skull was more elongated, with a low and sloping forehead, a prominent brow ridge, and a postorbital depression. They lacked a chin.