If you were to step into a time machine and go back 40 years, many major sports would look very different—and not just because of the odd uniform designs and questionable facial hair. The rules of the game were different.

Rule changes instituted over time have fundamentally altered the games we love, for better or for worse. Some were aimed at making a sport safer; others had the goal of making the games more entertaining or competitive; but many significantly changed the way the game is played.

Here are the five biggest rule changes in sports history.

1. The 2-Point Conversion

Believe it or not, the 2-point conversion wasn’t adopted by the NFL until 1994. The option to go for 2 had been a feature of the college game since 1958, but the NFL stuck to boring extra-point kicks for another 36 years. Since it came to the NFL, the 2-point conversion has added drama and excitement to the pro game. Say your team is down 16 points heading into the fourth quarter. Before 1993, you would have needed at least three possessions to take the lead. Today you only need two TDs and two 2-point conversions to tie the thing up.

There have also been numerous instances of teams electing to go for 2 and the win instead of 1 and the tie, which is always extremely scintillating. The bottom line: the 2-point conversion adds a fun, strategic twist while letting optimistic fans believe their team is never truly out of it. Yes, Raiders fans, we know your team only needs three TDs and three 2-point conversions to tie the game. No, Raiders fan, it’s not going to happen.

RELATED: The 9 Craziest Trick Plays in Sports History

2. The Designated Hitter

It’s a key element of modern baseball, but the designated hitter didn’t exist before 1973. Pitchers in both the American and National League had to dig into the batter’s box and take their chances against their opponents on the hill. Then American League officials realized that pitchers generally stink at hitting and that it’s more fun to watch beefy guys crush the ball than to see pitchers predictably whiff time after time. The DH was born, but only  in the American League. The National League still makes pitchers hit, which is probably why the AL is usually superior in every offensive category.

The advent of the DH allowed players who are phenomenal hitters but weak on defense to become superstars—players like Edgar Martinez and Harold Baines, who had decorated careers despite the fact that they hardly ever played in the field. David Ortiz has taken over 86 percent of his career at-bats as a DH, and Frank Thomas recently became the first Hall of Famer to take the majority of his at-bats (56.6%) as a DH. The DH makes games more exciting and adds an extra dimension to game management.

3. The 3-Point Line

If they were born a few decades earlier, NBA sharpshooters like Kyle Korver and Stephen Curry would have had to play a different style of basketball. That’s because the 3-point shot wasn’t adopted by the league until the 1979-1980 season. Legendary players like Oscar Robertson and Jerry West balled sans 3-pointers, so the game they played was much different than the one we see today. When the 3-point line was introduced in the NBA, many people saw it as a gimmick that would soon fade away. And in that first NBA season, players were tentative about shooting from deep—taking an average of only 2.8 triples per game and making only .8 (28.5%). Fast forward 35 years and 3-pointers are being shot—and swished—more than ever. In the average NBA game last season, shooters launched 21.5 3-pointers and knocked down 7.7 (36%).

Today’s NBA players have become so adept at shooting the deep ball that questions have been raised about whether the 3-point line should be moved back. This wouldn’t be unprecedented, since the line has already been moved several times. We’ve even heard talk about adding a 4-point line!

The addition of the 3-point line is arguably most impactful sports rule change in the last century, and it has spawned many amazing moments. Game-winning shots, 3-point shooting contests and insane heat checks wouldn’t be possible without the 3-point line.

RELATED: 4 Tips for Improving Your 3-Point Shooting Percentage

4. Offense-Friendly NHL Rule Changes

Following the 2004-2005 NHL lockout, many of the league’s head honchos were worried about low attendance and fan disinterest. Not only had the league missed an entire season’s worth of games, but the season before the lockout featured the fewest goals per game since 1955.

Although hardcore fans appreciate defensive battles, the casual fan enjoys goals and scoring chances. Thus, the NHL decided to make massive rule changes prior to the 2005-2006 season in an effort to increase scoring and entertainment. Penalties for hooking, holding, cross-checking and interference were mandated to be called more strictly, which forced defenders to be less aggressive.

The rink dimensions were changed to allow for more offensive movement and more quality chances on the power play. The two-line pass became legal, allowing for longer passes and making breakaways more frequent. Goaltender pads were made smaller, giving shooters more net to aim for. There were no more tie games, since shootouts would be used to decide the winner. These rules, along with many others, did serve their purpose. Several season scoring records were set and fan interest increased. How do we compare the stats of players like Alexander Ovechkin and Sidney Crosby, who’ve only played in the NHL under offense-friendly rules, to those of players like Mario Lemieux and Wayne Gretzky? We’ll leave that up to the Internet.

5. Replay Reviews

Fans never seem to run out of topics to argue about, but many agree on one thing—they want the right call to be made. So do the players, the coaches and the refs. Consequently, the use of replay review has grown in popularity in recent years. It seems now that you can’t watch a sporting event for more than an hour without a ref going to a booth, a monitor or a telephone to confirm that a call on the field or court was correct.

Now that MLB has adopted replay review, every major sport has its own replay review system. Although it can get tedious waiting for the refs to review every single possession in the closing minutes of the NBA Playoffs, we’d rather have them get it right than blow a call. It’s hard not to think how certain iconic sports moments would’ve played out had the refs been given the benefit of replay review. Thank goodness for technology.