It's thought that with the right atmospheric gases, Mars wouldn't have much trouble supporting life. Temperatures on Mars used to be very similar to what we experience here on Earth, and it even had running water back in the day. If they find life on Mars, it would suggest that life could actually be extremely common in the universe. They've been discovering a lot of solar systems near distant stars lately, and once the technology's refined enough to detect smaller planets at these distances, it's possible we could find a wealth of Earth-like planets in other solar systems.
Anyway I'm more than willing to bet Earth could still support life even if you made small but visibly noticeable changes to its orbit. Perhaps humans wouldn't have evolved if the orbit was changed, but many known forms of life have a far greater tolerance to extreme conditions than we do, and something else would have probably evolved in our place more suitable to the given climate.