How does Biogeography provide evidence for evolution?
Evidence of evolution comes from many different areas of biology. These evidences are body anatomy, embryology, biogeography, molecular biology, direct observation, and fossils study.
Here, in this post, we’ll only talk about the evidence of evolution from biogeography.
Biogeography is the study of the geographical distribution of organisms, that provides information about how, where, and when species may have evolved.
Biogeography provides us evolutionary data about the distribution of species in the various geographical regions of the earth and so that it can help us reconstruct their evolutionary histories and learn how evolution has taken place over the course of time.
It is the study of the distribution of species and ecosystems in the geographic space and through the geological timeframe.
This biogeographical study depends on the fact that the living organisms and their biological communities often vary in a regular fashion along geographic gradients of latitude, elevation, isolation, and habitat area.
Biogeography simply states that different geographical areas on earth had a different type of ancestral species that were better adapted to withstand their type of geographical environment.
Biogeography provides evidence for evolution as it helps us better understand how the present-day descendent species have evolved over time from those past-day ancestral species in their type of geographical areas where they were previously adapted.
How does Biogeography provide evidence for evolution? 5 Things to Know…
1. Species of a particular region share a common lineage
Biogeography supports the theory of evolution and describes the distribution of lifeforms over various geographical areas, both in the past and the present times.
It states that the species of a particular region share a common lineage (ancestry). This means that the ancestral species of a particular region have evolved to the many present-day descendent species over the course of evolution.
The biogeographical distribution states that closely related species are usually found in close physical proximity to one another and that fossils from these regions resemble modern organisms of that region.
If speciation was random, the distribution of species would be expected to be scattered all around. This suggests that these species from a particular region share a common lineage.
For example, it is seen that most of the Australian mammal species are marsupials (carry young ones in a pouch), while most mammal species found elsewhere in the world are placental (nourish young ones through a placenta).
This happened because Australia was isolated by water for millions of years, and so these species were able to evolve without competition from (or exchange with) other mammal species elsewhere in the world.
The marsupials of Australia due to their excessive presence have evolved themselves to create a diversity of various marsupial mammal species than the placental ones.
And so, it literally proves that species of a particular region share a common lineage which is evidence of biogeography.
2. Evidence from historical biogeography
Historical biogeography is a discipline of biogeography that is concerned with the origins and evolutionary histories of species on a long time scale in a particular geographical region.
Historical biogeography describes how, and when the species of a particular region have evolved and have lead to the creation of new species over time.
Various factors of microevolution and macroevolution that has occurred due to genetic drift, natural selection, adaptive radiation, etc. are all responsible for the speciation (creation of new species from ancestral species) in a particular geographical region.
Studying those factors of microevolution and macroevolution can provide us with clues and evidences from historical biogeography which had leads to massive evolution in the ancestral species.
Historical biogeographers depend heavily on evidence from other disciplines like fossil records, body anatomy, embryology, molecular biology to provide a large part of the information needed to determine distributions and past interactions.
Historical biogeographers also make use of a tool called an area cladogram which is actually a branching diagram showing the cladistic relationship between a number of species to find how those species are biogeographically related.
Thus historical biogeography allows scientists to determine how the differences in a particular geographical area and its environments affected the evolutionary history of different species of common origin.
For example: Evidence from historical biogeography shows that most modern marsupials (almost 70% of the extant species) are found exclusively in Australia. Australia has only a few placental mammals compared to South America, even though environmental conditions are similar between the two regions.
3. Evidence from ecological biogeography
Ecological biogeography helps in explaining and examining the distribution patterns of the various plants and animals from the viewpoint of their physiological needs and shows how they were related long ago, and is still related to their ecological niches.
Understanding the ecological along with the historical causes of present distribution patterns can help us to predict how the ancestral floras and faunas responded long before their evolution, and how their descendant species will respond to factors in the environment after their huge evolution and specialization, and thus help us to conserve their biodiversity.
Environmental factors such as temperature, humidity, salinity, predation-prey relationships, etc. are all considered as key elements in the ecological biogeography of many species.
When describing the ecological biogeography we also talk about the organism’s tolerances and responses to changes in moisture, temperature, soil chemistry, illumination, and other factors.
And it is seen that not many species share the same ecological niche, and as only a few of the species that will ever share the same ecological niche, evolution will tend to separate them.
This shows why the ancestral species have highly adapted to the change in its ecological and environmental factors due to natural selection over time and has lead to the present formation of many new-related species.
The evidences of the evolution of ecological biogeography can also be explained from factors like molecular homology, convergent and divergent evolution, etc.
For example, broad groupings of organisms that had already evolved before the breakup of the supercontinent Pangaea (about 200 million years ago) tend to be distributed worldwide. In contrast, broad groupings that evolved after the breakup tend to appear uniquely in smaller regions of Earth.
It is because of how their ecological factors forced them to better adapt themselves through natural selection which can be explained by the various ecological-biogeographical evolutionary studies.
4. Evidence from Island or Continental biogeography
One of the most significant pieces of proof for evolution comes from the study of island or continental biogeography. This is explained by how the evolutionary and plate tectonics theory influences biogeography.
Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of Earth’s lithosphere that occurred on Earth between 3.3 and 3.5 billion years ago.
Due to plate tectonics, many regions of the earth that previously had almost the same kind of related species were now isolated from each other due to the formation of many islands, and huge continents.
So, as a result, each of the islands and continents showed a huge variety of adaptations overtime in its inhabiting species with no occurrence of migration from one island/continent to another because each one was isolated from the other.
For instance, in the Finches on Galapagos islands, you will see that those species that eat large seeds tended to have large-tough beaks, while those that eat insects have thin-sharp beaks. All have originated from their ancestral seed-eating finches.
Island or continental biogeography in these remote locations like the Galapagos islands which was formed due to plate tectonics, Darwin noticed that there were unique species not found anywhere else.
Darwin observed that the species on both islands appeared to be closely related to the species on the nearest continent.
He concluded that the animals on these isolated islands must have been originated from the nearby continent, but because they were separated from the other species on the continent, they gradually evolved into something different over thousands of years.
Darwin’s observation showed that these finches were not found in similar climatic zones elsewhere on Earth but especially in the Galapagos Islands. This literally proves how island or continental biogeography led to the evolution of the finches.
5. Comparative biogeography as evidence of evolution
Comparative biogeography is the comparative study or comparison between two or more different biogeographical areas and comes to a conclusion on how evolution has occurred over time in contrast to these different biogeographical areas.
Comparative biogeography aims at identifying biologically meaningful areas, called “endemic areas” and at organizing them in a classification scheme according to their relationships.
In terms of evolution, comparative biogeographical studies show that how an ancestral species population of a particular area gets separated and isolated into various sub-populations in different-different areas, and later on, with the advancement of time these sub-populations adapt themselves into their type of environment of their particular area.
For instance, Darwin observed that the species on different Galapagos islands appeared to be closely related to the species on the nearest continent.
He concluded that the animals on these isolated islands must have been originated from the ancestral species of the nearby continent. But because they were separated from the other species on the continent, they gradually evolved into something different over thousands of years of evolution.
Another example of comparative biogeography is the lack of mammals on islands like Canary Islands or the Galapagos Islands.
It’s because the mammals that were present in these islands were not able to better adapt and so they got extinct over time.
Moreover, it was very unlikely for the other large mammals to travel over hundreds of miles of ocean water to reach such isolated islands from the nearby continent. And so, no mammals are still seen in these islands.
This also shows evidence of Comparative biogeography for evolution.
