Like neighbouring Keston, much of the Holwood Estate is situated on the free draining sands and gravels of the Blackheath Beds and in some areas still supports relict acid grassland and some heath. It has a long history of settlement going right back to about 200BC, during the Iron Age, when an extensive hillfort was built on the high ground. This consisted of 3 rings of ditches and banks and enclosed an area of about 100 acres. Since at least the 1750s Holwood has been managed as parkland with historic specimen trees though in the second half of the 20th century part of it was planted with conifers. It was the home of Prime Minister William Pitt between 1785 and 1802, and within the grounds of the estate, adjacent to a Public Footpath which crosses part of the site, are the remains of an old tree known as the Wilberforce Oak, beneath which William Wilberforce and William Pitt discussed the abolition of slavery. An entry in William Wilberforce’s diary for 1787 states,
"At length, I well remember after a conversation with Mr. Pitt in the open air at the root of an old tree at Holwood, just above the steep descent into the vale of Keston, I resolved to give notice on a fit occasion in the House of Commons of my intention to bring forward the abolition of the slave-trade."
This is commemorated by a stone seat put in place by Lord Stanhope, in 1862. He was an historian who also founded Cudham Church of England School, to the building and upkeep of which Darwin contributed. William Wilberforce’s son, Samuel, became the Bishop of Oxford and is remembered for his debate about evolution with Thomas Huxley which took place at the Oxford Union in 1860.
When Darwin and his family first moved to Downe, Holwood House belonged to Lord Cranworth. A Whig politician and twice Lord Chancellor, he contributed to the Downe Friendly Society of which Darwin was the Treasurer and which helped support local villagers. Charles and Emma regularly dined at Holwood and often visited the park, Darwin making many observations of plants and earthworms within the grounds. In particular he studied horse chestnut and meadow saxifrage and how there was a slight separation in time of maturation between the male and female parts of the flowers. This is called dichogamy and encourages some cross pollination (and therefore what is now termed genetic diversity) which is important for natural selection.
He also observed how insects became stuck to the sticky buds of horse chestnut in spring and how the sticky, pink glandular hairs of meadow saxifrage are similar to those of sundew. As with the latter, he experimented to see if meadow saxifrage leaves were able to absorb nitrogen in the form of ammonium carbonate but his results showed that meadow saxifrage absorbed little if any.
After the death of Lord Cranworth, Holwood became the home of Lord Derby and the Darwins continued to visit regularly. In 1881 Darwin experimented with the effect of immersing duckweed from Holwood in various solutions at differing strengths to see the effect these had on cell contents. This is recorded in a notebook held at Cambridge University Library (DAR 62: 56)
His earthworm studies carried out at Holwood include some work on how earthworms change landscape over time, recorded in, 'The formation of vegetable mould through the action of worms', in which he wrote,
"On some fine grassy slopes in Holwood Park, inclined at angles between 8 degrees and 11 degrees 30 seconds with the horizon, where the surface apparently had never been disturbed by the hand of man, castings abounded in extraordinary numbers: and a space 16 inches in length transversely to the slope and 6 inches in the line of the slope, was completely coated, between the blades of grass, with a uniform sheet of confluent and subsided castings. Here also in many places the castings had flowed down the slope, and now formed smooth narrow patches of earth, 6, 7, and 7.5 inches in length. Some of these consisted of two castings, one above the other, which had become so completely confluent that they could hardly be distinguished."
After Charles’ death Emma wrote to their son, William,
"Yesterday I drove to Keston to see Mrs Wright & walked back through Holwood Park – it was looking lovely – but seemed too full of memories, & I thought how you all used to race down the pretty green slope at the end – I was glad to think that I walked thro’ it w. your father not so very long ago – we used generally to finish a drive with that charming bit of walking."
Lord Derby was one of the pall-bearers at Darwin’s funeral and wrote that Darwin was,
"the greatest scientific discoverer of our age, [yet] free from jealousy or vanity in any form."