The Origin of New Species and Human Evolution

The Origin of New Species

The changes that living things experience as time passes lead to the creation of new species. In this long and complex process, there are 4 stages:

1. Production of Evolutionary Changes in Populations

This happens because natural selection favors some individuals and not others. As a consequence, the new populations are different from the original ones, although they still belong to the same species.

2. Genetic Isolation of the New Population

So that a new species can evolve, it is essential that the members of the new population do not reproduce with those of the previous population. In other words, they become independent and stop sharing genetic information with the original population.

3. Gradual Differentiation

After becoming isolated, the new population accumulates changes due to new mutations and gradually becomes more and more different from the original population.

4. Speciation

Over time, genetic changes produce such significant physical differences that it is no longer possible for the two populations to reproduce with each other, even if the isolation barriers have disappeared. From this moment, the populations are considered to be two distinct species.

5.1 Genetic Isolation Mechanisms

Genetic isolation is essential for speciation to take place. The barriers that can lead to the isolation of a species can be of different types:

• Geographical barriers: they stop physical contact between populations and as a result there are no crossings between them.
• Physiological barriers: they are incompatibilities in the way gametes work that prevent fertilization from happening, although individuals can mate.
• Chromosomal barriers: they are changes in the number or structure of chromosomes, which prevent the affected individuals from having offspring with the rest of the population.
• Ethological barriers: they are caused by the appearance of new types of behavior that result in the rejection of some individuals by others.

5.2 Microevolution

Present-day theories of evolution explain in a coherent and rational way the changes that lead to the appearance of new species and groups that are closely related to each other.

Macroevolution

The type of evolution that leads to large groups of organisms after drastic changes is known as evolution.

5.3 The Pace of Change

Gradualism
Macroevolution happens in the same way as microevolution, but under conditions that only happen under specific circumstances.

• The existence of anatomical structures that can create new organs.
• The accumulation of genetic variations that can allow rapid evolution in order to adapt to major environmental changes.
• The existence of habitats that had not been populated.
• The appearance of essential advantages in new groups.

Punctuated Equilibrium
Supporters find support in macroevolution because they claim that the appearance of major groups of organisms took place as a result of drastic changes and the accumulation of gradual variations.

5.4 Phylogenetic Trees

Phylogeny is the study of the evolutionary relationships living things have. A phylogenetic tree, also known as an evolutionary tree, is a visual representation of the evolutionary history of a group of organisms. At the base of a phylogenetic tree, we find the common ancestor from which all other groups formed. The successive branches correspond to speciation events that resulted in the appearance of new groups.

5.5 Biodiversity

It refers to the wide variety of living things that live on our planet.

Appearance of Humans

Humans are mammals, which means that they are affected by the same evolutionary mechanisms as all other living things. Humans belong to the order Primates. It is believed their characteristics were influenced by their adaptation to live in trees. They were the following:

• Their eye sockets are forward-facing and have stereotypical vision.
• Their forearm bone and muscle structure favor climbing.
• All the different species in this order have an opposable thumb in all four limbs, except for humans who only have it in their hands.
• They have flat nails instead of claws.

6.1 Hominidae Family

They are the most closely related to humans. There are two subfamilies:

• Ponginae: are large primates like orangutans.
• Homininae: are great apes. Humans belong to this subfamily.

Characteristics of gorillas:

• Quadruped.
• Longer arms than legs.
• Curved spine.
• Cranial capacity is less than 500 cm3.
• Highly developed canines.
• Opposable thumbs in hand and feet.
• Robust U-shaped jaw.
• Forward-facing eye sockets.
• Occipital crest.

6.2 Humanization Process

The members of the Homininae subfamily are characterized by their ability to maintain an upright position. Bipedalism could have originated in some groups of primates who were forced to stop living in trees because of a climate change, which happened around 15 million years ago and led to many trees. In the African savanna, being upright was an advantage because they had a better field of vision and they could use their hands for other things. The process of acquiring the particular characteristics of Homo sapiens is known as humanization.

• Acquisition of bipedalism.
• Shorter arms than legs.
• Spine with four curves.
• Skull capacity increases to 1500 cm3.
• Spherical skull with no crests.
• Foramen magnum in the inferior position.
• Decrease of prognathous jaws and brow ridges.
• Semi-circular jaw.
• Smaller canines.
• Opposable thumbs only present in hands.
• Acquisition of rational thinking, intelligence, language, and the ability to make art.
• Ability to make tools.

6.3 Main Representatives of the Genus Homo

Homo habilis: appeared 2.5 million years ago and became extinct 1.6 million years ago. Were able to walk upright, were 130 cm, and lived in Africa.
Homo ergaster: appeared 1.9 million years ago and disappeared 1.4 million years ago. Had 850 cm3 skull capacity and complex special relationships. Similar heights to humans.
Homo erectus: appeared 1.6 million years ago and disappeared 100,000 years ago. Around 170 cm tall, 1000 cm3 skull capacity, inhabited Africa, and colonized Europe and Asia.
Homo antecessor: they lived around 900,000 years ago. Considered to be Neanderthals' closest relative. Most ancient Homo in Europe. Skull capacity 1000 cm3.
Homo neanderthalensis: appeared 200,000 years ago and disappeared 35,000 years ago. 1500 cm3 and 165 cm tall. They practiced ritualistic burials and lived in Africa, Asia, and Europe.
Homo sapiens: appeared 200,000 years ago in Africa. 1400 cm3 and were 175 cm tall. They coexisted for some time with the Neanderthals. They were artistically talented.

6.4 The Phylogenetic Tree of the Human Species

Although fossils allow us to establish the changes that have taken place in the process of humanization, we still do not have a clear idea about our evolutionary lineage. The main difficulties faced by scientists are:

• Lack of fossils: we have not found enough fossils and sometimes they are just fragments, which are difficult to match with the correct species.
• Interpretations vary: sometimes, different scientists have classified the same fossils differently.