Macroevolution

Macroevolution is a big idea in science. It helps us learn how life on Earth changes over very long times. It looks at how new species are formed and how groups of animals or plants change and become different from each other. This is different from microevolution, which looks at small changes in one kind of organism, like changes in a group of butterflies.

One example of macroevolution is speciation. This is when a group of animals or plants splits into two or more new species. Scientists study macroevolution by looking at clues from fossils. Fossils show what life looked like millions of years ago. Scientists also compare the genes of different living things. They use a tool called phylogenetics. This tool helps make family trees for all kinds of organisms.

By using these clues, scientists can see patterns in how life has changed. They learn why some groups, like mammals, have many different species. Other groups, like some reptiles, have fewer species but look very different. This helps us understand the many kinds of life we see today and how they all connect 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 agreed that evolution was real but had different ideas about what caused it. Between the 1880s to the 1930s, a time 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 thought that genetics alone could not explain how new, larger groups of organisms developed.

Later, Theodosius Dobzhansky used the term in his important book 'Genetics und the Origin of Species' in 1937. Other scientists, like Richard Goldschmidt, also used the term but had different ideas about big changes in evolution. Dobzhansky believed that macroevolution was just many small changes happening over very long periods of time.

Microevolution vs Macroevolution

Micro- and macroevolution both show how life changes over time. Microevolution looks at small changes in one kind of living thing over many generations. These changes can happen because of mutation, natural selection, and genetic drift.

Macroevolution studies much bigger changes. These changes can create new kinds of living things and even groups of organisms. Scientists look at how these living things are related, what they find in the fossil record, and big events like mass extinctions. This helps us learn about the long history of life on Earth.

Macroevolutionary processes

Speciation

Main article: speciation

Speciation is when groups of the same species change so much that they can no longer have babies together. This creates new species and is a key part of macroevolution. Over time, these changes can lead to new groups of animals, like genres and families.

Evolution of new organs and tissues

One big question in evolution is how new parts, like organs, develop. Often, what look like brand-new organs are really changes to parts that already exist. For example, elephant tusks are changed teeth, and wings are changed arms. Even important parts like bone came from mixing existing proteins with minerals.

Examples

Evolutionary faunas

A key study in macroevolution looked at how many marine animals lived over time. The study shows how groups of marine animals grew and changed from the Cambrian period until today. Big changes in the environment and Earth shaped these changes.

Stanley's rule

Macroevolution looks at how new species appear and how some disappear. Species that create many new species often also disappear more often. This idea was first described by Steven Stanley. The Red Queen hypothesis suggests that when one species gets better adapted, others may have a harder time surviving. This shows how living things affect each other.

Evolution of multicellularity

Main article: Multicellular organism

One big step 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 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 part of the lizard family tree. Over many millions of 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 looks at big changes in life over very long times. Scientists study how new groups of animals appeared quickly, like in the Cambrian Explosion. They also study how the variety of life, called biodiversity, changes over time.

Other topics include how genes and development work together, known as Evo-devo. Scientists also study big events that caused many species to disappear, and how new species form while others vanish. They discuss ideas about whether evolution happens in quick bursts or very slowly.