We don't see souless animals acting in this fashion. When a member of a dolphin pod is injured the other dolphins gather around to protect it and keep it from drowning. When a member of a wolf pack is injured, the others make sure it still gets food and is cared for. The skeletal remains of Smilodons (saber-toothed cats) indicate severely-injured individuals were well cared for by others. Why would humans do anything less, even without divine command?
The Roman philosopher Seneca stated: "We drown our frail and sickly children". There will be about 40 million extra males in China in the next generation due to infant drownings, according to USA Today. Happens all throughout history. In fact in Rome it was legal to throw your children by the side of the road to die of exposure; these were called the "exposti" or 'exposed children'.
This practice was stopped in the Western world in 374 A.D. by the Christian emporor Valentinian I at the urging of Bishop Basil of Caesaria.
Why would we think that the animal kingdom is exempt from divine command?