Adaptive Radiation is a process of Macroevolution
Any type of evolution can take place on a small-scale or large-scale. Small-scale evolution is called microevolution, and large-scale evolution is called macroevolution.
Microevolution is just a small evolution like changing a few genes leading to the creation of new alleles within a population. Microevolution just leads to the change in allele frequencies in a gene pool.
Whereas, macroevolution is a very large-scale evolution that results from the sum total of all of the microevolution that took place within a population. This can lead to the formation of new species i.e speciation.
Adaptive radiation is a type of macroevolution because it leads to speciation that is the formation of new species. In such an evolutionary process, the ancestor species shows various small adaptations to its environment and gradually becomes different from the ancestor species after achieving many of such small adaptations altogether.
That’s why it is said that adaptive radiation is a type of evolutionary process in which an ancestral species gives rise to new species adapted to new habitats and new ways of life.
This type of evolution can take millions of years to happen as it includes the sum-total of all the small-scale adaptations in the ancestral form over the course of time.
The small-scale adaptations of the ancestral species are so-called microevolutions because it happens over short periods of time and constantly keep on happening to better adapt the species to its environment.
Whereas, on the other hand, many such small-scale adaptations of the ancestral species when added together can lead to a huge adaptation (also called evolution) over a longer period of time which is simply known as macroevolution.
If adaptive radiation is macroevolution, then what is microevolution
Microevolution is simply a change in gene/allele frequency within a population. Evolution at this scale can be observed over short periods of time that’s why it is also referred to as short-scale evolution.
Microevolution can occur over time within a population. This occurrence is due to five different processes viz. mutation, natural selection, artificial selection, gene flow, and genetic drift.
It is a kind of evolution in which the allele frequencies of a population keeps on changing over time from generation after generation. It’s an occurrence due to natural selection.
When scientists try to determine whether a population is evolving genetically they try to find microevolutionary changes, which is of course due to the change in its allele frequencies.
If they see the change in allele frequencies in a population as compared to that of the ancestral population than it is sure that the population is evolving in terms of genetics.
For example, the frequency of a gene for pesticide resistance in a population of crop pests increases between one generation and the next. Such a change might come about because natural selection favored the resistant genes that were being mutated from the non-resistant genes to pass to the future generations. This is just a small example of microevolution.
As when many of such or similar microevolutionary changes sum up to create a massive type of macroevolution, then adaptive radiation or convergent evolution can occur. Adaptive radiation is a pattern of how macroevolution occurs.
Often microevolution can lead to macroevolution as changes become more pronounced and two distinct species emerge. Both are caused by mutation, genetic drift, gene flow, or natural selection over long period of time.
We’ll learn more about how both adaptive radiation and convergent evolution is a pattern of macroevolution later in this post. So keep reading to understand the concept properly.
Fossils explain Adaptive Radiation pattern of macroevolution
In order to know if organisms have undergone Adaptive Radiation we need to have strong pieces of evidence. Studying those evidences will help us get proper clues of how, what, and where fossils have evolved.
And one drawback is that many of those ancestral species who had formed the present-day species aren’t alive to get those evidences.
So, we all know that the study of fossils (called Palaeontology) supports organic evolution. Studying fossils in different sedimentary layers indicates the geological time period in which they exist.
Microevolutionary changes usually occur in small timeframes and so are not frequently observed in the fossil records. It’s all because the processes that govern evolutionary changes within species are thought to occur over much shorter time scales that simply can’t be determined studying the sedimentary strata layers.
In contrast, macroevolutionary changes occur in large timeframes and so can be easily observed in the fossil records. It’s all because the evolutionary changes within species occur over much larger time scales (maybe between many thousands to millions of years) that can be easily determined by studying the sedimentary strata layers.
Thus the fossils help understand the macroevolution of organisms and recognize their evolutionary changes above the species level.
It is also to be mentioned that demonstrating adaptive radiation in fossil taxa can be especially problematic, as it is very hard to conduct the detailed functional tests necessary to document the existence of adaptations in long-extinct populations.
Also, note that adaptive radiation is not just evolution that creates only a single new species. In fact, Adaptive radiation is an evolutionary process that produces multiple new species from a single, rapidly diversifying lineage.
Example: Fossil record indicates that mammals underwent dramatic adaptive radiation to form thousands of present-day species after the extinction of terrestrial dinosaurs, about 65 million years ago. This is a perfect example of Adaptive Radiation due to mass extinction.
Adaptive Radiation is one of the patterns of Macroevolution
It is to be noted that the two important patterns of macroevolution are adaptive radiation and convergent evolution.
Adaptive Radiation studies often show that a single species has diversified over a longer time period into a clade containing many species.
Convergent Evolutionary studies show that sometimes different groups of organisms evolve in different places or at different times, but in similar environments. These organisms start out with different structures, but they face similar selection pressures.
Adaptive radiation is actually a type of divergent evolution because it occurs when two or more separate species evolve differently from a common ancestor.
Convergent evolution occurs when species have different ancestral origins but have developed similar features. Meaning that the descendent species that show similar adapting features have different ancestors.
In both cases, that is in both Adaptive radiation & Convergent evolution, macroevolution gradually takes place due to the various small adaptations taking place in the species body thus leading to speciation.
In Convergent Macroevolution, natural selection may mold different body structures of the different species in ways that perform similar functions but the body structures may look different.
In the Adaptive Radiation type of Macroevolution, natural selection may mold different body structures of the same ancestral species in ways that perform a lot of different functions but the body structures may look similar.
Is macroevolution a fact or a theory?
Evolution is both a fact and a theory and it’s when that evolution occurs at a large-scale which has been happening for a long period of time it is termed as macroevolution.
Evolution is widely observable in the laboratory and in the natural populations as they change over time. These are actually microevolutionary studies that can be done easily under such conditions.
But, macroevolutionary studies can’t be done so easily in the outside world or in any type of laboratory as these gradually needs thousands of years to complete which is not actually possible in any mean.
One thing is sure and is strongly obvious that small-small microevolutionary changes occurring over time can lead to a huge macroevolutionary change respectively that can lead to speciation. And adaptive radiation leading to speciation is just a type of macroevolution.
Macroevolution is a fact because it explains the larger evolutionary picture that is the appearance of the greater groups, such as the evolution of mammals, insects, and plants. It explains both the diversity of life and the pace of evolutionary change which is actually very strong evidence.
Macroevolution as a theory refers to evolutionary patterns and processes above the species level. It is usually contrasted with microevolution or evolutionary change within populations.