Outer space, as a place where Earth life will no doubt continue to travel, is hardly the sole province of humans. Other Earth life in orbit isn’t contained to your space crops and your space beef, and your experimental ant farm, either. Animals have a long history of going into space; in fact, they went there before we did, both to the academic definition of space, and in orbit.
Laika, of course, is famous for being the first creature of an Earth species to go into orbit, in the second orbiting spacecraft in “our” history. First sputnik, then muttnik, as Westerners called the spacecraft. She did not come back, because the technology for re-entry did not yet exist. We fired her into the heavens, and at least for that, she will always be first.
Several species intentionally made it into space before humans, including fruit flies, three different species of monkeys, and of course, dogs. The United States used monkeys for their space tests, but the Soviet Union preferred dogs, because they were better suited to long periods on inactivity. Laika, and many other cosmo-dogs were strays, “recruited” into the space program because they would have toughness that dogs with more domesticated lifestyles would not. A dog held the record for longest spaceflight until trumped by Skylab in 1973.
Here’s a list of other animal species that have gone into space:
fish (a mummichog, and later, zebra fish and others)
gypsy moth eggs
stick insect eggs
more recently tardigrades (which can survive in the vacuum of space without protection)
Naturally (because we are the top of the food and hierarchical ecosystem-control chain) many of these animals died on their heroic missions into the heavens. Some, like Laika, were not planned to survive their missions, but others died in accidents. There have been a good number of spaceflight accidents with both animals and humans, but the majority of the fatalities involve launch and re-entry. Only three people have died from decompression in space, on the Soyuz 11 in 1971. There were other near accidents and injuries in space, but most fatalities, like the loss of the Challenger and the Columbia shuttles, happened because of catastrophic equipment failure during the tremendous physical conditions of the heat and gravity effects of transiting to orbit.
This is not to say that orbit, or the vacuum of space is harmless. But the equipment required to support life in space is so complicated and multi-faceted, there are a myriad possibilities for something to go wrong (and in the case of near misses, to fix the problem) before animals or humans encounter the specific dangers of the space vacuum. In the case of launch and re-entry, the tolerances for failure are much slimmer. For instance, The actual explosion of the Challenger only caused the external propellant tank to collapse, but this caused the shuttle itself to veer into the Mach 1.8 windstream in a way not designed, which ripped the craft apart in seconds. And even then, it is estimated that the cockpit protected the astronauts inside for at least a time, because they deployed emergency oxygen. The crash of the shuttle into the ocean at 200 miles an hour was the definitive cause of death. (See STS-51F and STS-93 for other shuttle near-misses, in which the shuttle still made it into orbit.)
Once in space, animals must content with a few specific dangers from the vacuum of space. Although rapid decompression has been celebrated in SF as a cataclysmic way to go, the means of actually dying in a vacuum is actually pretty simple. The crucial danger of a space vacuum is hypoxia (lack of oxygen in the body), which might cause loss of consciousness after 9 to 12 seconds, but is generally survivable up to 90 seconds. This is not the same as asphyxiating; the lack of pressure causes all oxygen in the lungs to evaporate, and the circulating blood is instantly devoid of oxygen. The 9 to 12 seconds is how long this gasless blood takes to reach the brain. Hypoxia is accentuated by ebullism, which is the evaporation of liquid at low pressure, basically boiling the blood. Ebullism can be countered by space suits that reduce swelling. Survivability is much better if it’s only part of the body exposed to the vaccuum, and breathing can be maintained.
Temperature, however, is really not dangerous, because there is no medium for conduction in a vacuum. Radiation is the only way to cool, and that won’t happen before the other effects. So the portrayals of bodies freezing instantly in a vacuum are overwrought.
Rapid decompression is much more dangerous, intensifying the above. Slow decompressions of the same pressure gradient can be survivable, while rapid decompression can cause bleeding and shock, which use up the oxygen in the blood even faster.
If pressure is maintained, there are still long-term effects of being outside the Earth’s atmosphere and gravity. Gravity affects fluid movement through the body, and bone and muscle density. Radiation exposure outside the shelter of the atmosphere and magnetic fields of Earth is ten times normal for the surface. Long term effects could include cancer, chromosomal abberation, and immune system problems, but there hasn’t been enough data to study these fully. Also, circadian rhythm problems, social and psychological issues exist, but again, data is limited.
Since 1973, there has been a constant human presence in space, along with our animal friends. As far as I know, there have not been any long term experiments to test animals’ ability to evolve to space conditions. Certainly not with humans. There would have to be long-term, generational habitation in space to figure this out.
I synthesized this from a number of Wikipedia articles: