A Novel Theory of Evolution Describes Why Animals Decline With Time

A Novel Theory of Evolution Describes Why Animals Decline With Time | The Lifesciences Magazine


With its findings on species’ size variations, this research challenges conventional evolutionary ideas by revealing important variables underlying the gradual changes in some creatures’ sizes over time.

A recent study of the theory of evolution may have provided the answer to the question of why island lizards, cryptodiran turtles, and Alaskan horses have reduced over time.

According to recent theoretical research, the degree of direct rivalry between species for resources and the likelihood of environmental extinction are the two main ecological factors that determine an animal’s size throughout time.

Results of the Study and Ecological Aspects

The study, which was published today (Thursday, January 18) in the journal Communications Biology, uses computer models that simulate the theory of evolution to determine why some species gradually get smaller, as suggested by fossil records.

The study’s lead researcher, Dr. Shovonlal Roy, an ecosystem modeller from the University of Reading, stated: “Our research demonstrates that animal size can change over extended periods of time based on the habitat or environment, much as humans attempt to adapt to hot or cold weather depending on where we live.

Animal sizes frequently decrease in areas and periods where there is intense competition between various species for food and shelter as the species disperses and adjusts to the distribution of competitors and resources. For instance, due to changes in the climate and vegetation during the Ice Age, little horses that once existed in Alaska saw a fast reduction in size.

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“Sizes tend to increase where direct competition is less, however being extremely large and rare can make an animal more susceptible to extinction, as was the case with the dinosaurs.

“The fossil record reveals such perplexing mixes of size evolution patterns, with some lineages shrinking over time and others growing,” according to changes in ecological circumstances.

Cope’s Law

In order to conduct their investigation, the research team contested the inconsistencies between fossil evidence and “Cope’s rule.” Cope’s rule describes how some animal groupings have a propensity to evolve greater body sizes over millions and even thousands of years. The rule has the name of Edward Cope, a palaeontologist from the 19th century who is credited with spotting this pattern in the fossil record initially. For instance, the current horse evolved from its little, dog-sized progenitors through an evolutionary process of size expansion.

Fossil data, however, reveals strikingly contradictory patterns, with some groups seeing size increases and others experiencing size decreases.

Pressure from Evolution

The study used computer models to simulate the theory of evolution and found three different patterns of changing body size under various circumstances:

1. Gradual size growth over time

This occurs when differences in niches are less important in determining competition between species than their relative body sizes. For instance, over millions of years, the size of some genera of marine animal species—such as invertebrates—gradually expanded.

2. Size increase and extinctions follow

In this scenario, the largest animals frequently become extinct, creating chances for other species to emerge and develop even larger bodies, thereby perpetuating the cycle. Apex predators with huge bodies are most affected by mass extinctions. Particularly vulnerable to extinction are very huge mammals and birds, such as giant flying reptiles and dinosaurs.

3. A gradual reduction in size over time

The models also foresaw the species’ gradual shrinkage over time, which is the opposite of Cope’s rule. When there is a lot of rivalry and some overlap in the utilisation of resources and habitat, this occurs. There is evolutionary pressure on animals to shrink in size as they diverge into different niches. Reductions in size have previously been documented for island lizards, bony fish, cryptodiran turtles, vertebrates, and Pleistocene horses from Alaska.

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