Macroevolution

Macroevolution is a big idea in science that helps us understand how life on Earth changes over very long periods. It looks at how new species are formed and how groups of animals or plants, like families or orders, develop differences from each other. This is different from microevolution, which studies smaller changes that happen inside a single kind of organism, like variations in a population of butterflies.

One clear example of macroevolution is the process of speciation, when a group of animals or plants splits into two or more new species. Scientists study macroevolution by looking at clues from many places, such as fossils that show how life looked millions of years ago, and by comparing the genes of different living things. They also use a tool called phylogenetics, which helps draw family trees for all kinds of organisms.

By putting all these pieces together, scientists can see patterns in how life has changed. They learn why some groups, like the mammals, have many different species, while others, like certain types of reptiles, might have fewer but are very different in shape and size. This helps us understand the huge variety of life we see today and how it all connects back through time.

Origin and changing meaning of the term

After Charles Darwin published his book On the Origin of Species in 1859, many scientists accepted that evolution was real but disagreed about what caused it. During the years between the 1880s to the 1930s, called the 'Eclipse of Darwinism', some scientists supported ideas like 'orthogenesis'.

The term 'macroevolution' was first used by the Russian scientist Yuri A. Filipchenko in 1927. He believed that genetics alone could not explain how new groups of organisms, larger than a species, came to be.

Later, Theodosius Dobzhansky used the term in his important book 'Genetics und the Origin of Species' in 1937. Some other scientists, like Richard Goldschmidt, also used the term but had different ideas about how big changes in evolution might happen. Dobzhansky thought that macroevolution was just many small changes adding up over very long periods of time.

Microevolution vs Macroevolution

Micro- and macroevolution are both supported by overwhelming evidence. Microevolution looks at changes within a single species, like small shifts in traits over generations. It involves mutation, natural selection, and genetic drift.

Macroevolution, on the other hand, studies bigger changes that lead to new species and even whole groups of organisms. It looks at how species are related, patterns in the fossil record, and events like mass extinctions. Scientists study these big changes to understand the deep history of life on Earth.

Macroevolutionary processes

Speciation

Main article: speciation

Speciation is the process where populations of one species change so much that they can no longer interbreed. This creates new species and is an important part of macroevolution. Over long periods, these changes can lead to the development of new groups of animals, such as genera and families.

Evolution of new organs and tissues

One big question in evolution is how new structures, like organs, come to be. Often, what seem like brand-new organs are actually changes to existing ones. For example, elephant tusks are modified incisors, and wings are modified limbs. Even major tissues like bone formed from combining existing proteins with minerals.

Examples

Evolutionary faunas

A key study in macroevolution is Sepkoski's research on marine animal diversity over time. His famous diagram shows how the numbers of marine families changed from the Cambrian period to today. It highlights how three groups of marine animals, called "evolutionary faunas," grew and shrank over millions of years, influenced by big ecological changes and geological events.

Stanley's rule

Macroevolution depends on how often new species appear and how often they go extinct. Interestingly, species that create many new species often also face high extinction rates. This idea, first described by Steven Stanley, is supported by the Red Queen hypothesis, which suggests that as one species becomes better adapted, others may struggle to keep up, leading to their extinction. This pattern shows how living things affect each other's survival and evolution.

Evolution of multicellularity

Main article: Multicellular organism

One of the biggest steps in evolution was the development of organisms made of many cells. The first step is for single-celled organisms to stick together. This can happen with just a few changes in their genes. For example, some bacteria and yeast can become multicellular with just one gene change, forming clusters of cells.

Evolution of bat wings

The wings of bats share the same basic bone structure as other mammals with five fingers. What makes bat wings special is that their finger bones are much longer. Scientists have found that certain genes, like bone morphogenetic proteins, are more active in bats, causing these bones to grow longer. By studying bat genes, researchers have been able to make mice develop longer bones, showing how these changes happen.

Limb loss in lizards and snakes

Main article: Limbless vertebrates

Snakes evolved from lizards and are actually part of the lizard family tree. Over about 180 million years, snakes lost their limbs. We have fossils that show the steps in this process. Limb loss has happened in many reptile groups, including skinks, where some species have fully developed limbs, while others have shorter and shorter limbs, and some have no limbs at all.

Human evolution

Human evolution involved changes in our brains rather than our bodies. While our physical appearance didn't change much from our primate ancestors, our brains developed in ways that allowed for consciousness and intelligence. Studying human and ape genomes helps scientists understand the genetic changes that led to these brain developments.

Evolution of viviparity in lizards

Most lizards lay eggs, but some give birth to live young, like most mammals. In some lizard groups, species that lay eggs have evolved into species that give live birth with only small genetic changes. For example, a European lizard species gives birth to live young in most places but lays eggs in the far southwest. Similar changes happen in South American lizards living at higher altitudes, showing that switching from laying eggs to live birth doesn't need many genetic changes.

Research topics

Macroevolution studies big changes in life over long periods. Researchers look at how new groups of animals appear quickly, like in the Cambrian Explosion, and how the variety of life changes through time, known as biodiversity.

Other topics include how genes and development work together, known as Evo-devo, big events that wipe out many species called mass extinctions, and how new species form and others disappear. Scientists also study debates about whether evolution happens in quick bursts or slowly over time.