• Skip to primary navigation
  • Skip to main content
  • Skip to footer
  • About
  • Image & Use Policy
  • Translations
  • Glossary

SUPPORT UE

  • Email
  • Facebook
  • Twitter

UC MUSEUM OF PALEONTOLOGY

UC Berkeley logoUC Berkeley

Understanding Evolution

Understanding Evolution

Your one-stop source for information on evolution

Understanding Evolution

  • Home
  • Evolution 101
    • An introduction to evolution: what is evolution and how does it work?
      • 1_historyoflife_menu_iconThe history of life: looking at the patterns – Change over time and shared ancestors
      • 2_mechanisms_menu_iconMechanisms: the processes of evolution – Selection, mutation, migration, and more
      • 3_microevo_menu_iconMicroevolution – Evolution within a population
      • 4_speciation_menu_iconSpeciation – How new species arise
      • 5_macroevo_menu_iconMacroevolution – Evolution above the species level
      • 6_bigissues_menu_iconThe big issues – Pacing, diversity, complexity, and trends
  • Teach Evolution
    • Lessons and teaching tools
      • Teaching Resources
      • Image Library
      • Using research profiles with students
      • Active-learning slides for instruction
      • Using Evo in the News with students
      • Guide to Evo 101 and Digging Data
    • Conceptual framework
      • Alignment with the Next Generation Science Standards
      • teach-evo-menu-icon
    • Teaching guides
      • K-2 teaching guide
      • 3-5 teaching guide
      • 6-8 teaching guide
      • 9-12 teaching guide
      • Undergraduate teaching guide

    • Misconceptions about evolution

    • Dealing with objections to evolution
      • Information on controversies in the public arena relating to evolution
  • Learn Evolution

Home → Is there a trend toward complexity?
  • ES en Español

Is there a trend toward complexity?

How can we define complexity? To get a handle on it, we might compare the number of different types of cells or the number of genes within a species.

If we simply compare the life that was probably around 3.5 billion years ago to the life that is around today, it is obvious that the “average” level of complexity is higher today than it was at life’s origins. But this is probably just because when life started out, it was at its lowest limit of complexity. It had nowhere to go but up!

What happens if we ignore the early history of life and just look at evolution after life had become reasonably complex? If life has the opportunity of going either up or down the complexity scale, does it tend to go up?

The answer to this question is simply that we’re not sure — it depends where you look. There are many cases of simplification (for example, some insects have lost their wings) and others in which lineages have become increasingly complex (for example, some insects wings have evolved into complex organs for flight control).

1. Simplification or loss

Photos of a stick insect on the left and an oat flower on the right.
Some stick insect lineages lost wings in the course of their evolution (left). A simplified and reduced wild oat flower (right). Stick insect photo courtesy of Robert Potts © California Academy of Sciences; Wild oat flower © 2003 James B. Gratiot.

2. Increased complexity

Photos of cranefly on the left and a woodcut of a human brain on the right.
Evolution has modified the hindwings of flies into halteres, organs that help them control their flight (left). The relatively complex human brain (right). Fly photo courtesy of Dr. Antonio J. Ferreira © California Academy of Sciences; Brain woodcut by Andreas Vesalius

There is no clear evidence available at this point for an overall trend towards complexity in the history of life. Besides, a lot of “simple” organisms are still around! The entire history of life could be referred to as the “Age of Bacteria” because bacteria have been and still are ubiquitous, since the beginning of life on Earth. Just a thought.

Black and white microscopic photo of ecoli bacteria.
Relatively “simple” bacteria might still be considered the rulers of the Earth. Bacteria micrograph © Free University of Brussels (U.L.B.).

Footer

Connect

  • Email
  • Facebook
  • Twitter

Subscribe to our newsletter

Teach

  • Teaching resource database
  • Correcting misconceptions
  • Conceptual framework and NGSS alignment
  • Image and use policy

Learn

  • Evo 101
  • Evo in the News
  • The Tree Room
  • Browse learning resources
  • Glossary

Copyright © 2023 · UC Museum of Paleontology Understanding Evolution · Privacy Policy