On Wednesday, the Texas State Board of Education signed off on a preliminary version of the state's pared-down biology curriculum and voted to keep language that challenges the theory of evolution.

Over the last few decades, the topic of teaching evolution has caused plenty of controversy across the states. Here are some of the ways states have dealt with the issue of how to teach evolution -- or whether to teach it at all.

Alabama:

In 1995 Alabama’s Board of Education voted to place stickers on public school biology books that said evolution is a “controversial theory” and “any statement about life’s origins should be considered as theory, not fact.” Though it has been updated throughout the years, the disclaimer has been used with Alabama textbooks for the last two decades.

Florida:

In 2008, Florida’s Board of Education required that evolution be taught in public schools for the first time ever.

Georgia:

In 2002, the Cobb County school board placed stickers on biology books that said “evolution is a theory, not a fact, regarding the origin of living things.” They removed the stickers in 2005 after a federal judge ruled it unconstitutional.

Louisiana:

A 2008 law allowed public school teachers to provide supplemental educational materials to help students understand evolution. A 2014 lawsuit said one school district promoted religion and taught creationism.

Tennessee:

A 2012 law said, “the teaching of some scientific subjects, including, but not limited to, biological evolution, the chemical origins of life, global warming, and human cloning, can cause controversy” and that teachers must help students understand, analyze, critique and review the theory of evolution.

Wisconsin:

The state requires public schools to teach evolution, but school districts may determine the specifics of their science curriculum.

Next Generation Science Standards are used as a means of teaching evolution in public schools. Twenty-six states have adopted this common set of guidelines: Arizona, Arkansas, California, Delaware, Georgia, Illinois, Iowa, Kansas, Kentucky, Maine, Massachusetts, Michigan, Minnesota, New Jersey, New York, North Carolina, Ohio, Oregon, Rhode Island, South Dakota, Tennessee, Vermont, Washington and West Virginia.

Major Court Cases Involving Evolution:

Epperson v. Arkansas (1968): It established the precedent that a state curriculum could not be tailored to fit religious beliefs or principles. The court ruled that an Arkansas statute prohibiting the teaching of evolution to be unconstitutional.

Segraves v. State of California (1981): Kelly Segraves sued the state, arguing her children's right to free exercise of religion was violated by the teaching of evolution. The court ruled that it did not violate their rights.

McLean v. Arkansas Board of Education (1982): The court ruled Arkansas' balanced treatment of creation-science and evolution-science statute violated the law.

Edwards v. Aguillard (1987): The court ruled Louisiana's Creationism Act - which only allowed evolution to be taught in public schools if it was taught with creation science - to be unconstitutional.

Peloza v. Capistrano Unified School District (1991): A biology teacher sued the California school district for being forced to teach evolution without discussing his personal religious beliefs. The Supreme Court declined to review the case after it was appealed.

Freiler v. Tangipahoa Parish Board of Education (1997): This Louisiana school board required teachers to read a disclaimer that defended the Biblical version of creation before teaching evolution. The court ruled this unconstitutional.

Kitzmiller v. Dover (2005): A Pennsylvania federal district court ruled that intelligent design was a form of creationism and unconstitutional to teach in public schools.